Filter flow rates and retention times

Filter requirements and calculations
Calculating ideal flow rates and filter retention times for koi pond filtration systems can sometimes be contradictory and for the average koi keeper with modest stocking levels and a reasonable filter there shouldn't be a problem. But there are a lot of over-stocked ponds with
pretty poor filtration systems - find out why.

Let's get complicated
When it comes to filter sizing, life can get complex. As I've said, if we only wanted simple nitrification, it is probable that filter sizes would be small. However, as well as nitrification koi-keepers want:
# gin-clear' water
# breakdown & removal of DOC,
# conditions which discourage filamentous algae (blanketweed)
# generally optimal water conditions for fish.
In trying to meet these wide-ranging demands filters are built far larger than they would be if based on the required SSA of filter media alone.

The longer the better
Broadly speaking, the effectiveness of biological filtration is improved the longer the 'polluted' water is held in the filter - i.e. the longer the retention time. The most time-consuming process in filtration is the breakdown of dissolved organic carbon compounds into simple inorganic compounds. These compounds are ultimately incorporated back into living organisms. This complex chain of processes is not instantaneous and will, even under ideal circumstances, take some time. If insufficient filtration time is available, intermediate products will be pumped out of the filter back into the pond. This is clearly undesirable and rather defeats the object of having a filtration system. Indeed, this may well be the reason why excessive algal growth occurs in some ponds, with the filter merely producing an endless supply of plant nutrients! So for how long should water be retained in the biological section?
This depends on how polluted the water is in the first place. Certainly, industrial water treatment plants - which handle much higher levels of pollution from sewage etc. - would retain water in the plant for many hours before it was deemed sufficiently clean to return to the
nearest water-course. Given that pond water is likely to be only mildly polluted, a retention time of ten minutes, possibly longer, will usually suffice. The more polluted the water is, the longer it needs to be retained in the filter. Most koi ponds will require a retention time of at least a few minutes. So how do you calculate the retention time of your filter?
This is determined by the flow rate and the volume of water in the filter. If water output from the filter is 2,000 gallons/hour and the filter contains 500 gallons (when full of media) of water then: filter retention time = filter size/pump rate, so, in our example:
retention time = 500 (litres) / 2000 (litres / hour flow rate) = 0.25 hours (which is 15 minutes).
so a given sample of water will take 15 minutes to pass through the filter and back to the pond
In the above, the filter capacity represents the amount of water in the filter - not the physical size of the filter, which will be greater. The retention time or the size of the filter will depend to a
very large extend on the type of filtration medium used. A solid medium with low void space such as gravel will occupy much more filter space than large-pored, lightly packed media and therefore leads to a lower retention time.

More calculations!
Using our same example of a 500 gallon filter. If we now nearly fill it with gravel, the volume of water it will hold will be reduced substantially - maybe to as little as 150 to 200 gallons. Using the above example, the retention time of such a filter would now become;
200/2000 = 0.1 hours (6 minutes) or less This compares the original estimate of a retention time of 15 minutes. In comparison, if the same filter was filled instead with matting or plastic, there would be hardly any displacement and the filter will probably still hold in excess of 450 gallons, giving a retention time over double that of gravel. So a filter with a dense, low-void medium, such as gravel, will need to be substantially larger than one based on light-weight media, in order to achieve the same retention time, which explains why koi filters were traditionally so large. The retention time and therefore the filter size will depend on the filter media used. Cheaper, dense media such as gravel will need larger filters to achieve the same efficiency as lightweight media.

The quicker the better?
Just when everything starts to make sense, along comes a complication. While a longer filter retention time will produce better water quality we also have to consider pond turnover times. Why? Because polluted water is produced in the pond and, if there was a slow turnover at the filter, it would take longer for pond water to get processed by the filter. To make sense of pond turnover rates it is helpful to return to the original analogy of koi being sewage-making machines: expensive food in one end and sewage out the other. Our seemingly impossible aim should be to remove this pollution as fast as it is produced. If we can manage that then we would have perfect water conditions most of the time. When we are considering pollution the primary concern is not so much the volume of water, but rather the number of fish and the amount of food we feed - because this is what determines both the amount of metabolic ammonia and the quantity and quality of solid waste. There are several ways to calculate ammonia production in a koi pond. A rough and ready estimate can be made based on the amount of food fed each day.
Each kilogram of fish food will result, on average, in 37 grams of ammonia being produced, together with copious faeces. And there is other organic waste, such as that from decomposing algae and micro­ organisms. The important point is that as the stocking, and thereby feeding level, is increased the water will have to be treated at an ever quicker rate if water quality is to be maintained.
# If, for instance, we had a pond of 20,000 litres (4,500 gallons) and the fish were fed 200 grams of food per day, this would produce approximately 7.5 grams (7,500mg) of ammonia per day, an average of say 300 mg per hour. (In reality the ammonia level would fluctuate throughout the day, being highest shortly after feeding).
# At this feeding rate, if no ammonia was removed, at the end of a day the ammonia content of the water would be 24 x 300 mg ammonia = 7 200 mg in 20,000 litres of pond water, giving an ammonia concentration of 0.37 mg/litre, which is too high.
# Conversely, if it was possible to remove the ammonia at the same rate as it is produced - namely, 300 mg per hour - the steady state ammonia level would be zero. To remove ammonia this quickly we would have to pass the entire contents of the pond through the filter every hour,
giving a flow-rate of 20,000 litre/hour, otherwise there will always be some residual ammonia present.
# Deep breath! - If, instead of a flow-rate of 20,000 litre/hour, we had a flow rate of the pond volume every two hours - or half the pond volume every hour (same thing), an oversimplified calculation would give:
# 300 mg ammonia / 20 000 litres (pond volume) x 10000 (flow rate litre/hour) = 150 mg ammonia removed per hour, leaving 150mg in the pond, or a steady state of >0.01 mg / litre. (This makes the simplifying assumption that there is no nitrification occurring in the pond.)
# We can see the effects of increased stocking and / or feeding levels if we take an exaggerated example in which we treble the feeding rate to 600 mgs of food per day 600 grams of food per day would produce around 900 mg ammonia per hour.
With the same flow rate we would remove 900 mg ammonia / 20,000 litres (pond volume) x 10 000 (flow rate litres /hour) = 450 mg ammonia removed per hour leaving 450 mg in the pond, or a steady state of 0.02 mg /litre, an increasingly unacceptable level. Clearly the only way to balance the increased ammonia production would be to 'feed' the ammonia to the filter at an ever increasing rate. I should stress that the above examples are an over-simplification of what actually happens since other factors, such as nitrification in the pond rather than in the filter, also have to be taken into account. Indeed, where the flow rates or filter retention times are less than optimum, an increasing proportion of the ammonia nitrification will take place in the pond rather than the filter. While it is not immediately important where in the system nitrification takes place – it does help to explain why some ponds are more upset as a consequence of disease treatments than others. However, if flow-rates are kept constant and the feeding rate is increased, there will be a steady increase in the background level of ammonia. It is not necessary to get any further involved in calculations, the important point is that when high feeding/stocking levels are involved, the flow-rate is an important factor in determining the ammonia removal rate.

Adequate flow-rate
So what is an adequate flow­rate? As explained, it depends on the feeding rate. The most commonly quoted advice is: turn over the volume of the pond between 8 and 12 times a day. But it is important to remember that this is a rule of thumb and flow-rates may well need to be increased for higher feeding and/or stocking rates. Certainly, koi- keepers who feed in excess of 0.25 kg of food per day may have to consider increasing flow rates, particularly if there is a periodic ammonia problem. Conversely, it may be possible to have a slower rate when feeding levels drop, as they do in winter. The pond flow rate is dependent on the total ammonia produced within the system, With higher stocking densities there has to be a corresponding increase in flow rate. In an average koi pond, a flow rate of 1/2 to 1/3 of pond volume per hour should suffice.

Filter size
Taking retention times and flow rates into consideration, when it comes to choosing the right filter size, there are two important but conflicting factors:
# the right filter retention time, which ensures all the required biological activity occurs,
# brisk water flow to prevent a high pond ammonia level. If we decide that a flow-rate of say 10,000 litres per hour (2,200 gal/hour) and a filter retention time of 10 minutes are required then the volume of water in contact with the filter media at any time will need to be;
10,000/60 (minutes) x 10 (minutes retention time) = 1666 litres or 1.6m3.
This means that the filter should be able to hold 1.6 m3 of water after it is filled with media. This is in addition to settlement and spaces below the media trays. The required size of filter will then depend on the media used. Using a high-void medium, such as matting or plastic, we would need a little over 1.6 m3 of media to compensate for the small amount of water displacement, whereas, with a solid medium, we might need at least 3m3 to ensure the same volume of water in contact with the media after displacement. Although this may seem complex, these are the factors which need to be considered to avoid some of the most common filtration problems which often beset koi-keepers - namely, fluctuating water quality, high levels of opportunistic micro-organisms and excessive algal growth. The size of a filtration system becomes more critical as stocking level, and thereby feeding rates, increase. Even when no new fish are added, the continued growth of the existing pond occupants will gradually increase the demand on filter performance. Ideally, what we want is a fairly brisk flow-rate, turning over the pond volume every 1 to 3 hours (depending on feeding and stocking rate) but at the same time a slow, almost imperceptible flow through the filter, allowing sufficient time for the various important biological processes to occur. Water passing through the filter should be in contact with the filter media, and therefore the biofilm, for at least ten minutes, possible longer.

WATER QUALITY

pH
Why Is it Important?
The pH of a sample of water is a measure of the concentration of hydrogen ions. The term pH was derived from the manner in which the hydrogen ion concentration is calculated - it is the negative logarithm of the hydrogen ion (H+) concentration. What this means to those of us who are not mathematicians is that at higher pH, there are fewer free hydrogen ions, and that a change of one pH unit reflects a tenfold change in the concentrations of the hydrogen ion. For example, there are 10 times as many hydrogen ions available at a pH of 7 than at a pH of 8. The pH scale ranges from 0 to 14. A pH of 7 is considered to be neutral. Substances with pH of less that 7 are acidic; substances with pH greater than 7 are basic.

The pH of water determines the solubility (amount that can be dissolved in the water) and biological availability (amount that can be utilized by aquatic life) of chemical constituents such as nutrients (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, cadmium, etc.). For example, in addition to affecting how much and what form of phosphorus is most abundant in the water, pH may also determine whether aquatic life can use it. In the case of heavy metals, the degree to which they are soluble determines their toxicity. Metals tend to be more toxic at lower pH because they are more soluble.

Reasons for Natural Variation
Photosynthesis uses up dissolved carbon dioxide which acts like carbonic acid (H2CO3) in water. CO2 removal, in effect, reduces the acidity of the water and so pH increases. In contrast, respiration of organic matter produces CO2, which dissolves in water as carbonic acid, thereby lowering the pH. For this reason, pH may be higher during daylight hours and during the growing season, when photosynthesis is at a maximum. Respiration and decomposition processes lower pH. Like dissolved oxygen concentrations, pH may change with depth in a lake, due again to changes in photosynthesis and other chemical reactions. There is typically a seasonal decrease in pH in the lower layers of a stratified lake because CO2 accumulates. There is no light for plants to fix CO2 and decomposition releases CO2.

Fortunately, lake water is complex; it is full of chemical "shock absorbers" that prevent major changes in pH. Small or localized changes in pH are quickly modified by various chemical reactions, so little or no change may be measured. This ability to resist change in pH is called buffering capacity. Not only does the buffering capacity control would-be localized changes in pH, it controls the overall range of pH change under natural conditions. The pH scale may go from 0 to 14, but the pH of natural waters hovers between 6.5 and 8.5.

Expected Impact of Pollution
When pollution results in higher algal and plant growth (e.g., from increased temperature or excess nutrients), pH levels may increase, as allowed by the buffering capacity of the lake. Although these small changes in pH are not likely to have a direct impact on aquatic life, they greatly influence the availability and solubility of all chemical forms in the lake and may aggravate nutrient problems. For example, a change in pH may increase the solubility of phosphorus, making it more available for plant growth and resulting in a greater long-term demand for dissolved oxygen.

Values for pH are reported in standard pH units, usually to one or two decimal places depending upon the accuracy of the equipment used.
Since pH represents the negative logarithm of a number, it is not mathematically correct to calculate simple averages or other summary statistics.
Instead, pH should be reported as a median and range of values; alternatively the values could be converted to hydrogen ion concentrations, averaged, and re-converted to pH values.

Generally, during the summer months in the upper portion of a productive or eutrophic lakes, pH will range between 7.5 and 8.5. In the bottom of the lake or in less productive lakes, pH will be lower, 6.5 to 7.5, perhaps. This is a very general statement to provide an example of the differences you might measure.

The Case of Acid Rain
An important exception to the buffering of pH changes in lakes is the case of lakes affected by acid rain. Lakes that have received too much rain with a low pH (acid rain), lose their buffering capacity. At a certain point, it takes only a small bit of rain or snowmelt runoff for the pH to change. After that point, change occurs relatively quickly. According to the EPA, a pH of 5-6 or lower has been found to be directly toxic to fish.

Turbidity
Why Is it Important?
Turbidity refers to how clear the water is.The greater the amount of total suspended solids (TSS) in the water, the murkier it appears and the higher the measured turbidity. The major source of turbidity in the open water zone of most lakes is typically phytoplankton, but closer to shore, particulates may also be clays and silts from shoreline erosion, resuspended bottom sediments (this is what turns the western arm of Lake Superior near Duluth brown on a windy day), and organic detritus from stream and/or wastewater discharges. Dredging operations, channelization, increased flow rates, floods, or even too many bottom-feeding fish (such as carp) may stir up bottom sediments and increase the cloudiness of the water.

High concentrations of particulate matter can modify light penetration, cause shallow lakes and bays to fill in faster, and smother benthic habitats - impacting both organisms and eggs. As particles of silt, clay, and other organic materials settle to the bottom, they can suffocate newly hatched larvae and fill in spaces between rocks which could have been used by aquatic organisms as habitat. Fine particulate material also can clog or damage sensitive gill structures, decrease their resistance to disease, prevent proper egg and larval development, and potentially interfere with particle feeding activities. If light penetration is reduced significantly, macrophyte growth may be decreased which would in turn impact the organisms dependent upon them for food and cover. Reduced photosynthesis can also result in a lower daytime release of oxygen into the water. Effects on phytoplankton growth are complex depending on too many factors to generalize.

Very high levels of turbidity for a short period of time may not be significant and may even be less of a problem than a lower level that persists longer. The figure below shows how aquatic organisms are generally affected.


Reasons for Natural Variation
Algal turbidity varies seasonally and with depth in a complex manner as discussed previously in response to physical, chemical and biological changes in the lake. Inorganic and detrital particles from the watershed vary largely in response to hydrological events such as storms and snowmelt.

Even relatively small amounts of wave action can erode exposed lakeshore sediments, in this case a minepit lake from northeastern Minnesota. Can you guess what mineral was mined here?

Impacts
The major effect turbidity has on humans might be simply aesthetic - people don't like the look of dirty water. However, turbidity also adds real costs to the treatment of surface water supplies used for drinking water since the turbidity must be virtually eliminated for effective disinfection (usually by chlorine in a variety of forms) to occur. Particulates also provide attachment sites for heavy metals such as cadmium, mercury and lead, and many toxic organic contaminants such as PCBs, PAHs and many pesticides.

Turbidity is reported by RUSS in nephelometric units (NTUs) which refers to the type of instrument (turbidimeter or nephelometer) used for estimating light scattering from suspended particulate material. Turbidity can be measured in several ways. Turbidity is most often used to estimate the TSS (total suspended solids as [mg dry weight]/L) in the lake's tributaries rather than in the lake itself unless it is subject to large influxes of sediments. For the WOW project we will attempt to develop empirical (meaning: based upon direct measurements) relationships between TSS and turbidity for each system since turbidity is easily measured and TSS analyses are not very sensitive at the typically low concentrations found in the middle of most lakes. Also, TSS is a parameter that directly relates to land uses in the watershed and is a key parameter used for modeling efforts and for assessing the success of mitigation and restoration efforts.

What in the world are Nephelometric Turbidity Units (NTU’s)?
They are the units we use when we measure Turbidity. The term Nephelometric refers to the way the instrument estimates how light is scattered by suspended particulate material in the water. The Nephelometer, also called a turbidimeter, attached to the RUSS unit has the photocell (similar to the one on your camera or your bathroom nightlight) set at 90 degrees to the direction of the light beam to estimate scattered rather than absorbed light. This measurement generally provides a very good correlation with the concentration of particles in the water that affect clarity.

In lakes and streams, there are 3 major types of particles: algae, detritus (dead organic material), and silt (inorganic, or mineral, suspended sediment). The algae grow in the water and the detritus comes from dead algae, higher plants, zooplankton, bacteria, fungi, etc. produced within the water column, and from watershed vegetation washed in to the water. Sediment comes largely from shoreline erosion and from the resuspension of bottom sediments due to wind mixing.

Usually, we measure turbidity to provide a cheap estimate of the total suspended solids or sediments (TSS) concentration (in milligrams dry weight/L). TSS measurement requires you to filter a known volume of water through a pre-weighed filter disc to collect all the suspended material (greater than about 1 micron in size) and then re-weigh it after drying it overnight at ~103°C to remove all water in the residue and filter. This is tedious and difficult to do accurately for low turbidity water - the reason why a turbidimeter is often used. Another even cheaper method is to use an inexpensive devise called a Turbidity Tube. This is a simple adaptation for streams of the Secchi disk technique for lakes. It involves looking down a tube at a black and white disk and recording how much stream water is needed to make the disk disappear.
This device yields data for streams that is similar to a secchi depth measurement in lakes. As for secchi measurements are made in the shade with the sun to your back to make an accurate and reproducible reading - the shadow of the observer should be adequate.

1. Pour sample water into the tube until the image at the bottom of the tube is no longer visible when looking directly through the water column at the image. Rotate the tube while looking down at the image to see if the black and white areas of the decal are distinguishable.
2. Record this depth of water on your data sheet to the nearest 1 cm. Different individuals will get different values and all should be recorded, not just the average. It is a good idea to have the initials of the observer next to the value to be able identify systematic errors.
3. If you see the image on the bottom of the tube after filling it, simply record the depth as > the depth of the tube. Then construct a longer tube, more appropriate for your stream.

Turbidity is a standard measurement in stream sampling programs where suspended sediment is an extremely important parameter to monitor. It may also be useful for estimating TSS in lakes, particularly reservoirs, since their useful lifetime depends upon how fast the main basin behind the dam fills with inflowing sediments from mainstem and tributary streams and from shoreline erosion. In the WOW lakes, direct inputs of sediments from tributaries are probably too low to significantly affect the turbidity of the water column out in the main lake. However, algal densities, particularly in the more eutrophic lakes in the Minneapolis Metro area represent enough particulate material to be easily measureable by the RUSS turbidity sensors. Although chlorophyll sensors (fluorometers) would be the best way for us to estimate algal abundance (we lack the funding at present), in these lakes the turbidity sensors provide an alternate estimate of algae.

Why Is it Important?
The secchi disk depth provides an even lower "tech" method for assessing the clarity of a lake. A Secchi disk is a circular plate divided into quarters painted alternately black and white. The disk is attached to a rope and lowered into the water until it is no longer visible. Secchi disk depth, then, is a measure of water clarity. Higher Secchi readings mean more rope was let out before the disk disappeared from sight and indicates clearer water. Lower readings indicate turbid or colored water. Clear water lets light penetrate more deeply into the lake than does murky water. This light allows photosynthesis to occur and oxygen to be produced. The rule of thumb is that light can penetrate to a depth of about 2 - 3 times the Secchi disk depth.

Clarity is affected by algae, soil particles, and other materials suspended in the water. However, Secchi disk depth is primarily used as an indicator of algal abundance and general lake productivity. Although it is only an indicator, Secchi disk depth is the simplest and one of the most effective tools for estimating a lake's productivity.

Reasons for Natural Variation
Secchi disk readings vary seasonally with changes in photosynthesis and therefore, algal growth. In most lakes, Secchi disk readings begin to decrease in the spring, with warmer temperature and increased growth, and continue decreasing until algal growth peaks in the summer. As cooler weather sets in and growth decreases, Secchi disk readings increase again. (However, cooler weather often means more wind. In a shallow lake, the improved clarity from decreased algal growth may be partly offset by an increase in concentration of sediments mixed into the water column by wind.) In lakes that thermally stratify, Secchi disk readings may decrease again with fall turnover. As the surface water cools, the thermal stratification created in summer weakens and the lake mixes. The nutrients thus released from the bottom layer of water may cause a fall algae bloom and the resultant decrease in Secchi disk reading.

Rainstorms also may affect readings. Erosion from rainfall, runoff, and high stream velocities may result in higher concentrations of suspended particles in inflowing streams and therefore decreases in Secchi disk readings. On the other hand, temperature and volume of the incoming water may be sufficient to dilute the lake with cooler, clearer water and reduce algal growth rates. Both clearer water and lower growth rates would result in increased Secchi disk readings.

The natural color of the water also affects the readings. In most lakes, the impact of color may be insignificant. But some lakes are highly colored. Lakes strongly influenced by bogs, for example, are often a very dark brown and have low Secchi readings even though they may have few algae.

Expected Impact of Pollution
Pollution tends to reduce water clarity. Watershed development and poor land use practices cause increases in erosion, organic matter, and nutrients, all of which cause increases in suspended particulates and algae growth.

Secchi disk depth is usually reported in feet to the nearest tenth of a foot, or meters to the nearest tenth of a meter. Secchi disk readings can be used to determine a lake's trophic status. Though trophic status is not related to any water quality standard, it is a mechanism for "rating" a lake's productive state since unproductive lakes are usually much clearer than productive lakes.

Dissolved Oxygen
Why Is It Important?
Like terrestrial animals, fish and other aquatic organisms need oxygen to live. As water moves past their gills (or other breathing apparatus), microscopic bubbles of oxygen gas in the water, called dissolved oxygen (DO), are transferred from the water to their blood. Like any other gas diffusion process, the transfer is efficient only above certain concentrations. In other words, oxygen can be present in the water, but at too low a concentration to sustain aquatic life. Oxygen also is needed by virtually all algae and all macrophytes, and for many chemical reactions that are important to lake functioning.

Reasons for Natural Variation
Oxygen is produced during photosynthesis and consumed during respiration and decomposition.Because it requires light, photosynthesis occurs only during daylight hours. Respiration and decomposition, on the other hand, occur 24 hours a day. This difference alone can account for large daily variations in DO concentrations. During the night, when photosynthesis cannot counterbalance the loss of oxygen through respiration and decomposition, DO concentration may steadily decline. It is lowest just before dawn, when photosynthesis resumes.

Other sources of oxygen include the air and inflowing streams. Oxygen concentrations are much higher in air, which is about 21% oxygen, than in water, which is a tiny fraction of 1 percent oxygen. Where the air and water meet, this tremendous difference in concentration causes oxygen molecules in the air to dissolve into the water. More oxygen dissolves into water when wind stirs the water; as the waves create more surface area, more diffusion can occur. A similar process happens when you add sugar to a cup of coffee - the sugar dissolves. It dissolves more quickly, however, when you stir the coffee.

Another physical process that affects DO concentrations is the relationship between water temperature and gas saturation. Cold water can hold more of any gas, in this case oxygen, than warmer water. Warmer water becomes "saturated" more easily with oxygen. As water becomes warmer it can hold less and less DO. So, during the summer months in the warmer top portion of a lake, the total amount of oxygen present may be limited by temperature. If the water becomes too warm, even if 100% saturated, O2 levels may be suboptimal for many species of trout.


Mid-summer, when strong thermal stratification develops in a lake, may be a very hard time for fish. Water near the surface of the lake - the epilimnion - is too warm for them, while the water near the bottom - the hypolimnion - has too little oxygen. Anoxia forces the fish to spend more time higher in the water column where the warmer water is suboptimal for them. This may also expose them to higher predation, particularly when they are younger and smaller.

Eutrophication exacerbates this condition by adding organic matter to the system which accelerates the rate of oxygen depletion in the hypolimnion. Urban, and other forms of runoff, can also add to this problem very suddenly and dramatically by causing fish kills after excess soils and road hydrocarbons are washed in from intense rainstorms. Conditions may become especially serious during a stretch of hot, calm weather, resulting in the loss of many fish. You may have heard about summertime fish kills in local lakes that likely results from this problem.

In eutrophic and hypereutrophic lakes, summertime fish kills can happen most easily during periods with high temperatures, little wind and high cloud cover. The clouds reduce daytime photosynthesis with its oxygen production and so the DO in the mixed layer. Or even throughout the water column of a shallow unstratified lake, can become critical for fish and other aquatic organisms.

The same basic phenomenon can occur in winter (winterkill) when ice cover removes re-aeration from the atmosphere and snowcover can light-limit algal and macrophyte photosynthesis under the ice. Many lakes in the upper midwest are mechanically re-aerated or injected with air, oxygen or even liquid oxygen to keep ice off of some of the lake and to add oxygen directly to prevent winterkills.

Dissolved oxygen concentrations may change dramatically with lake depth. Oxygen production occurs in the top portion of a lake, where sunlight drives the engines of photosynthesis. Oxygen consumption is greatest near the bottom of a lake, where sunken organic matter accumulates and decomposes. In deeper, stratified, lakes, this difference may be dramatic - plenty of oxygen near the top but practically none near the bottom. If the lake is shallow and easily mixed by wind, the DO concentration may be fairly consistent throughout the water column as long as it is windy. When calm, a pronounced decline with depth may be observed.

Seasonal changes also affect dissolved oxygen concentrations. Warmer temperatures during summer speed up the rates of photosynthesis and decomposition. When all the plants die at the end of the growing season, their decomposition results in heavy oxygen consumption. Other seasonal events, such as changes in lake water levels, volume of inflows and outflows, and presence of ice cover, also cause natural variation in DO concentrations.

Expected Impact of Pollution
To the degree that pollution contributes oxygen-demanding organic matter (like sewage, lawn clippings, soils from streambank and lakeshore erosion, and from agricultural runoff) or nutrients that stimulate growth of organic matter, pollution causes a decrease in average DO concentrations. If the organic matter is formed in the lake, for example by algal growth, at least some oxygen is produced during growth to offset the eventual loss of oxygen during decomposition. However, in lakes where a large portion of the organic matter is brought in from outside the lake, oxygen production and oxygen consumption are not balanced and low DO may become even more of a problem.

The development of anoxia in lakes is most pronounced in thermally stratified systems in summer and under the ice in winter when the water mass is cut-off from the atmosphere. Besides the direct effects on aerobic organisms, anoxia can lead to increased release of phosphorus from sediments that can fuel algal blooms when mixed into the upper euphotic (sunlit) zone. It also leads to the buildup of chemically reduced compounds such as ammonium and hydrogen sulfide (H2S, rotten egg gas) which can be toxic to bottom dwelling organisms. In extreme cases, sudden mixing of H2S into the upper water column can cause fish kills.

Dissolved oxygen concentrations are most often reported in units of milligrams of gas per liter of water - mg/L. (The unit mg/L is equivalent to parts per million = ppm).

DO - % saturation
Oxygen saturation is calculated as the percentage of dissolved O2 concentration relative to that when completely saturated at the temperature of the measurement depth. Recall that as temperature increases, the concentration at 100% saturation decreases. The elevation of the lake, the barometric pressure, and the salinity of the water also affect this saturation value but to a lesser extent. In most lakes, the effect of dissolved solutes (salinity) is negligible; but the elevation effect due to decreased partial pressure of oxygen in the atmosphere as you go up (recall the breathing difficulties faced by Mt. Everest climbers) is about 4% per 300 meters (1000 feet). The DO concentration for 100% air saturated water at sea level is 8.6 mg O2/L at 25°C (77°F) and increases to 14.6 mg O2/L at 0°C.

Electrical Conductivity
Why is it important?
Electrical conductivity (EC) estimates the amount of total dissolved salts (TDS), or the total amount of dissolved ions in the water. EC is controlled by:

1. geology (rock types) - The rock composition determines the chemistry of the watershed soil and ultimately the lake. For example, limestone leads to higher EC because of the dissolution of carbonate minerals in the basin.

2. The size of the watershed (lake basin) relative to the area of the lake (Aw : Ao ratio) - A bigger watershed to lake surface area means relatively more water draining into the lake because of a bigger catchment area, and more contact with soil before reaching the lake.

3. "other" sources of ions to lakes - There are a number of sources of pollutants which may be signaled by increased EC:

a. wastewater from sewage treatment plants (point source pollutants; see: links)
b. wastewater from septic systems and drainfield on-site wastewater treatment and disposal systems (nonpoint source pollutants; see: links )
c. urban runoff from roads (especially road salt; see: links). This source has a particularly episodic nature with pulsed inputs when it rains or during more prolonged snowmelt periods. It may "shock" organisms with intermittent extreme concentrations of pollutants which seem low when averaged over a week or month (see: Measures of Variability Lesson and other links)
d. agricultural runoff of water draining agricultural fields typically has extremely high levels of dissolved salts (another major nonpoint source of pollutants; see: links). Although a minor fraction of the total dissolved solids, nutrients (ammonium-nitrogen, nitrate-nitrogen and phosphate from fertilizers) and pesticides (insecticides and herbicides mostly) typically have significant negative impacts on streams and lakes receiving agricultural drainage water. If soils are also washed into receiving waters, the organic matter in the soil is decomposed by natural aquatic bacteria which can severely deplete dissolved oxygen concentrations (see above).
e. atmospheric inputs of ions are typically relatively minor except in ocean coastal zones where ocean water increases the salt load ( "salinity" ) of dry aerosols and wet (precipitation) deposition. This oceanic effect can extend inland about 50-100 kilometers and be predicted with reasonable accuracy.

4. evaporation of water from the surface of a lake concentrates the dissolved solids in the remaining water - and so it has a higher EC. This is a very noticeable effect in reservoirs in the southwestern US (the major type of lake in arid climates), and is, of course, the reason why the Great Salt Lake in Utah and Mono Lake, California and Pyramid Lake, Nevada are so salty.

5. bacterial metabolism in the hypolimnion when lakes are thermally stratified for long periods of time (in Minnesota this might be May - November depending on the basin shape, lake depth and weather). During this period, there is a steady "rain" of detritus (dead stuff, mostly algae and washed in particulate material from the watershed) down to the bottom. This material is decomposed by bacteria in the water column and after it reaches the sediments. Their metabolism releases the potential energy stored in the chemical bonds of the organic carbon compounds, consumes oxygen in oxidizing these compounds, and releases carbon dioxide (CO2) after the energy has been liberated (burned). This CO2 rapidly dissolves in water to form carbonic acid (H2CO3), bicarbonate ions (HCO3- ) and carbonate ions (CO3-) the relative amounts depending on the pH of the water. This newly created acid gradually decreases the pH of the water and the "new" ions increase the TDS, and therefore the EC, of the hypolimnion. Essentially, they are "eating" organic matter much as we do and releasing CO2. We oxidize organic carbon using O2 that we breathe out of the air as an oxidant. We use the energy to drive our metabolism and exhale the oxidized carbon as CO2. The oxygen is simultaneously chemically reduced and exhaled as water vapor (H2O; the oxidation state of gaseous molecular oxygen is reduced from 0 to -2 in the process). Other higher aquatic organisms that have aerobic metabolisms, such as zooplankton, insects and fish also consume oxygen dissolved in the water while releasing carbon dioxide as they metabolize organic carbon (food items).

What in the world are microSiemens per centimeter (µS/cm)?
These are the units for electrical conductivity (EC). The sensor simply consists of two metal electrodes that are exactly 1.0 cm apart and protrude into the water. A constant voltage (V) is applied across the electrodes. An electrical current (I) flows through the water due to this voltage and is proportional to the concentration of dissolved ions in the water - the more ions, the more conductive the water resulting in a higher electrical current which is measured electronically. Distilled or deionized water has very few dissolved ions and so there is almost no current flow across the gap (low EC). As an aside, fisheries biologists who electroshock know that if the water is too soft (low EC) it is difficult to electroshock to stun fish for monitoring their abundance and distribution.

Up until about the late 1970's the units of EC were micromhos per centimeter (µmhos/cm) after which they were changed to microSiemens/cm (1 µS/cm = 1 µmho/cm). You will find both sets of units in the published scientific literature although their numerical values are identical. Interestingly, the unit "mhos" derives from the standard name for electrical resistance reflecting the inverse relationship between resistance and conductivity - the higher the resistance of the water, the lower its conductivity. This also follows from Ohm’s Law, V = I x R where R is the resistance of the centimeter of water. Since the electrical current flow (I) increases with increasing temperature, the EC values are automatically corrected to a standard value of 25°C and the values are then technically referred to as specific electrical conductivity.

All WOW conductivity data are temperature compensated to 25°C (usually called specific EC). We do this because the ability of the water to conduct a current is very temperature dependent. We reference all EC readings to 25°C to eliminate temperature differences associated with seasons and depth. Therefore EC 25°C data reflect the dissolved ion content of the water (also routinely called the TDS or total dissolved salt concentration).

How much salt is there in lakewater?
The image below was developed to give you an idea of how much salt (dissolved solids and ions) is present in some of the WOW lakes and to compare them to a range of other aquatic systems. TDS, in milligrams per liter (mg/L) stands for total dissolved salts or solids and is the weight of material left behind were you to filter a liter of water to remove all the suspended particulates and then evaporate the water from the container (usually done in a drying oven in the lab unless you work on Lake Mead in southern Nevada where you can just set it outside for a few minutes in the summer). Each of the piles represents the amount of salt present in a liter of water. We used sodium bicarbonate (baking soda) for the lakes and sodium chloride (table salt) for the ocean.

Chlorophyll - A Measure of Algae
An in-depth microscopic enumeration of the dozens of species of algae present in a water column each time a lake is sampled is prohibitively costly and technically impossible for most monitoring programs. Further, in many lakes a large portion of the algal biomass may be unidentifiable by most experts (these are appropriately called LRGTs or LRBGTs -- little round green things and little round blue-green things). However, measuring the concentration of chlorophyll-a is much easier and provides a reasonable estimate of algal biomass. Chlorophyll-a is the green pigment that is responsible for a plant's ability to convert sunlight into the chemical energy needed to fix CO2 into carbohydrates. To measure chlorophyll-a, a volume of water from a particular depth is filtered through a fine glass-fiber filter to collect all of the particulate material greater than about 1 micron (1/1000th of a millimeter) in size. The chlorophyll-a in this material is then extracted with a solvent (acetone or alcohol) and quantified using a spectrophotometer or a fluorometer.

Both chlorophyll-a and secchi depth are long-accepted methods for estimating the amount of algae in lakes. Secchi depth is much easier and less expensive to determine. However, care must be used in interpreting secchi data because of the potential influence of non-algal particulate material, such as silt from stream discharge or re-suspended bottom sediment. Also, the tea color of some lakes that's due to dissolved organic matter from bogs, can have an effect on secchi depth readings as well. Even if chlorophyll-a is measured, it may be important to also examine the algal community microscopically on occasion, since the mix of species may influence lake management decisions.

Temperature
Why Is it Important?
Most aquatic organisms are poikilothermic - i.e., "cold-blooded" - which means they are unable to internally regulate their core body temperature. Therefore, temperature exerts a major influence on the biological activity and growth of aquatic organisms. To a point, the higher the water temperature, the greater the biological activity. Fish, insects, zooplankton, phytoplankton, and other aquatic species all have preferred temperature ranges. As temperatures get too far above or below this preferred range, the number of individuals of the species decreases until finally there are few, or none. For example, we would generally not expect to find a thriving trout fishery in ponds or shallow lakes because the water is too warm throughout the ice-free season.

The Q10 Rule
Changes in the growth rates of cold-blooded aquatic organisms and many biochemical reaction rates can often be approximated by this rule which predicts that growth rate will double if temperature increases by 10°C (18°F) within their "preferred" range.

Q10 rule
Temperature is also important because of its influence on water chemistry. The rate of chemical reactions generally increases at higher temperature, which in turn affects biological activity. An important example of the effects of temperature on water chemistry is its impact on oxygen. Warm water holds less oxygen that cool water, so it may be saturated with oxygen but still not contain enough for survival of aquatic life. Some compounds are also more toxic to aquatic life at higher temperatures. Temperature is reported in degrees on the Celsius temperature scale(C).

Reasons for Natural Variation
The most obvious reason for temperature change in lakes is the change in seasonal air temperature. Daily variation also may occur, especially in the surface layers, which are warm during the day and cool at night. In deeper lakes (typically greater than 5 m for small lakes and 10 m for larger ones) during summer, the water separates into layers of distinctly different density caused by differences in temperature. Unlike all other fluids, however, as water approaches its freezing point and cools below 4°C, the opposite effect occurs and its density then begins to decrease until it freezes at 0°C (32°F). This is why ice floats. This process is called thermal stratification. The surface water is warmed by the sun, but the bottom of the lake remains cold. You can feel this difference when diving into a lake. Once the stratification develops, it tends to persist until the air temperature cools again in fall. Because the layers don't mix, they develop different physical and chemical characteristics. For example, dissolved oxygen concentration, pH, nutrient concentrations, and species of aquatic life in the upper layer can be quite different from those in the lower layer. It is almost like having two separate lakes. The most profound difference is usually seen in the oxygen profile since the bottom layer is now isolated from the major source of oxygen to the lake - the atmosphere.

When the surface water cools again in the fall to about the same temperature as the lower water, the stratification is lost and the wind can turbulently mix the two water masses together because their densities are so similar (fall turnover). A similar process also may occur during the spring as colder surface waters warm to the temperature of bottom waters and the lake mixes (spring turnover). The lake mixing associated with a turnover often corresponds with changes in many other chemical parameters that in turn affect biological communities. Watch for these changes in your lake this fall and spring.

Because light deceases exponentially with depth in the water column, the sun can heat a greater proportion of the water in a shallow lake than in a deep lake and so a shallow lake can warm up faster and to a higher temperature. Lake temperature also is affected by the size and temperature of inflows (e.g., a stream during snowmelt, or springs or a lowland creek) and by how quickly water flushes through the lake. Even a shallow lake may remain cool if fed by a comparatively large, cold stream.

Expected Impact of Pollution
Thermal pollution (i.e., artificially high temperatures) almost always occurs as a result of discharge of municipal or industrial effluents. Except in very large lakes, it is rare to have an effluent discharge. In urban areas, runoff that flows over hot asphalt and concrete pavement before entering a lake will be artificially heated and could cause lake warming, although in most cases this impact is too small to be measured. Consequently, direct, measurable thermal pollution is not common. In running waters, particularly small urban streams, elevated temperatures from road and parking lot runoff can be a serious problem for populations of cool or cold-water fish already stressed from the other contaminants in urban runoff. During summer, temperatures may approach their upper tolerance limit. Higher temperatures also decrease the maximum amount of oxygen that can be dissolved in the water, leading to oxygen stress if the water is receiving high loads of organic matter. Water temperature fluctuations in streams may be further worsened by cutting down trees which provide shade and by absorbing more heat from sunlight due to increased water turbidity.

REFERENCES
Michaud, J.P. 1991. A citizen's guide to understanding and monitoring lakes and streams. Publ. #94-149. Washington State Dept. of Ecology, Publications Office, Olympia, WA, USA (360) 407-7472.
Moore, M.L. 1989. NALMS management guide for lakes and reservoirs. North American Lake Management Society, P.O. Box 5443, Madison, WI, 53705-5443, USA (http://www.nalms.org).

Mahseer/Kelah

INTRODUCTION
Mahseer is acclaimed as a world famous outstanding game and food fish of India. As a sport fish, it provides unparalleled recreation to anglers from all over the world, better than salmon. It is known as tiger in waters, because of the fight it musters to wriggle off the hook. Anglers come to the Cauvery River in southern India in search of these mighty mahseer.In Northern Europe, you have the leaping salmon. In Russia and Mongolia, you have the ferocious taimen. In North America, the inscrutable muskellunge. And in South America, the humongous arapaima. These are some of the biggest and most challenging river fish you can find and international anglers are willing to pay big money to pit wits with them. In parts of South and South-East Asia, there is a large-scaled fish that can match or even surpass the strength and stamina of these fish.

For some, this fish has no equal. Half carp and half barbell, it thrives in the fast currents of rocky rivers, and can shoot up tall rapids and even small waterfalls. When hooked by an angler, it can fight for hours before it succumbs – if the angler is lucky enough not to have his line broken or hook straightened out!

In the past, mahseer formed a substantial natural fishery in the major riverine and lacustrine ecosystems of India. In commercial fisheries it occupies an important position for its good quality. For the fishermen mahseer is of considerable importance because of its large size. As a food fish, it is highly esteemed and fetches the high market price. The mahseer (tor tambroides’ and ‘tor Douronensis), known in Malaysia as ikan kelah - Red Finned Mahseer, Ikan Kelah Merah/ Merah Bara from Pahang/Terengganu and Ikan Kelah Merah Rebung from Kelantan, Semah/ Empurau from Sarawak, Pelian from Sabah, Kelah Hijau/ Kejor/Tengas - Malaysian, Semah/ Garing from Sumatra Indonesia, Blue Thai Mahseer from Thailand, Golden Burmese from Burma. In the Mekong basin lives the Chinese Mahseer (Tor sinensis). In India and Myanmar, you have the Golden Mahseer (Tor putitora and Tor tor)are large cyprinids inhabiting the clear, pristine and fast flowing waters of Asia, from the cool waters of Himalayan streams to the tropical rivers of South East Asian jungles. Rapid development in the watersheds within the natural range of many Tor species habitats, particularly the spawning grounds, is increasing pressure and threatening their survival. This has resulted in depletion of natural stocks and consequently some species have become rare, threatened and/or endangered. In view of their conservation value and the aquaculture potential, there are concerted efforts amongst researchers, developers, planners and conservationists and governments all across Asia to enhance the natural populations in rivers and natural water bodies.
Day (1878) believed that mahseer constituted only one species. Hora (1940) confirmed the validity of six different species. A recent critical study on the subject by Menon (1992) confirmed 6 valid species. He has, however, described a new species from the Darna River (Godavari drainage) at Deolali, Nashik District of Maharashtra, and named it Tor kulkarnii, which he describes as a dwarf cognate of Tor khudree. Preserntly seven valid species are recognized for India:


Scientific Name ....................... Common Name
Tor putitora (Ham.) -------------- Golden or putitora mahseer
Tor tor (Ham.) ------------------- Turiya or tor mahseer
Tor khudree (Sykes) -------------- Deccan or khudree mahseer
Tor mussullah (Sykes) ------------ Humpback or mussullah mahseer
Tor kulkarnii ---------------------- Dwarf mahseer
Tor progeneius (McClelland) ------- Jungha of the Assamese
Tor mosal (Sykes) ---------------- Copper or mosal mahseer

In addition to the above, three sub-species, viz., Tor mosal mahanadicus, Tor khudree malabaricus and Tor khudree longispinis are considered by Desai (2002) as valid species, with some reservations. Different species of mahseer occupy different ecosystems ranging from tropical waters where summer temperatures reach 35°C, to sub-Himalayan regions, where the temperatures fall to 6°C. Similarly, they occur in streams hardly above sea level and are also found at an altitude of 2000 m above sea level. Jhingran and Sehgal (1978) remarked that the occurrence and distribution of mahseer is controlled by the prevailing water temperature of the streams and not by the altitude.

Mahseers were considered as carnivorous and slow growing and thus unsuitable for fish culture. However, a careful study of the feeding habits of mahseer indicating that it is omnivorous has dispelled the notion that mahseer are carnivorous. Studies on the anatomical adaptations of the alimentary canal system also confirm that mahseer are omnivorous. Tripathi (1995) suggested the inclusion of mahseer in polyculture, cage culture and for river ranching and has stated that mahseer would not compete with mrigal (Cirrhinus mrigala) and the common carp. The importance of mahseers as a World-famous game fish is well known. The group comes in a spectrum of colours from deep burnt copper, through gold, silver, dark black, and inhabit different rivers through out the length and breadth of India, Pakistan, Burma, Bangladesh Srilanka, and even Thailand, (Thomas, 1897). Among the seven different recorded species (viz. Tor putitora, T. mussulah, T.khudree, T mosal, T. progeneius, T. tor and Acrossocheilus hexangonolepis). Tor putitora or golden mahseer is one of the most-sought after species providing the main fishery in the uplands all along the Himalayan belt extending from Kashmir in the north-west to Sadiya in the north-east. The fish is also known as Greyhound or the thick-lipped mahseer and has been observed to attain the weight of 70-80 kg. (Misra, 1962). Anglers regard golden mahseer as one of the finest sport-fish and it is a source of recreation to innumerable sportsmen both Indian & Foreigner Thomas, 1897 in his famous book " The Rod in India" stated that pound for pound mahseer is far superior to ‘lordly salmon’ in sporting qualities. To the local fishermen too, mahseers have been of considerable importance because of their large size, hardy texture, high commercial value and longer shelf life.

In recent years due to their proximity to human intervention, mahseer stock is threatened with multifaceted dangers posed by construction of series of dams, barrages/ weirs across the rivers on one hand and over-exploitation on the other. While uncontrolled fishing and destructive fishing devices have adversely affected the riverine population, the construction of dams are acting as physical barrier to this migratory species, tending to prevent their access to their usual breeding and feeding grounds. Dams interrupt the river continuum and block the longitudinal connectivity of rivers. They also generate a complex web of impacts which affect the physical and biological components of the riverine environment. The denial of migration also results in permanent and irrevocable eradication of fish stock ranging from depletion to complete extermination. The ever-diminishing catches of mahseer from the river Satluj, Giri, Beas, Chenab and their tributaries clearly bespeaks the affects caused by the construction of Pandoh, Chamera, Pong, Bhakra & Giribata barrages. Regardless of their height, weirs and dams constitute barriers to breeding migration of mahseer. Further, mahseer population is also affected by morphological modifications resulting from completion of river valley projects. These include change in slope, river-bed profile, submersion of gravel zones or riffle section as well as destruction of riparian vegetation and changes in tropic regimes. Most of the negative factors affect upper parts of the streams where lacustrine conditions are superimposed on the river. Downstream, the hydrological conditions get severely altered through reduction of water discharge. The adverse conditions of the flow can extend over many kilometers downstream of the obstruction so that fish passages become difficult.

Indiscriminate hooking, netting, dynamiting and electrocuting have also greatly affected the mahseer availability in the State’s rivers and streams. In the pursuit of more and more catches, even the declared State’s sanctuaries have not been spared by the poachers. Further, due to reduced availability of large mahseer in the streams, fishing pressure on juveniles is on the increase with the result that streams earlier assuring a bountiful harvest have started giving a dismal picture. The various anglers’ Associations have painted a similar picture of other States of the country. Once teeming with thousands of mahseer, streams like Giri, Ashwani, Binwa Neugal, Beas, etc. the returns are sharply declining, raising the number of disgruntled anglers each year. Mahseer is known to be an omnivore fish in its adult stage. In earlier days considering the mouth opening and massive size, the fish was supposed to be a carnivore (Malhotra, 1982).

However, we have collected many samples from rivers of Pokhara Valley, where gut contained rice grain, small insects and plants. Mahseer therefore appears to be an opportunistic feeder which feeds on a wide variety of food of plant and animal origin. Mahseer have been found to also feed on green filamentous algae, insect larvae, small molluscs, and algal coatings on rocks (Shrestha, 1997; Negi, 1994; Dubey, 1985). Nautiyal and Lal (1984) reported that in natural habitat food of mahseer fingerlings consisted of insect matter (81.4 percent), plant matter (15.9 percent) and other items including fish (1.6 percent). Knowledge of natural feeding habits of mahseer would provide a basis for formulated feed development for this species. Studies on nutrition and feed management for different developmental stages of mahseer are a prerequisite for farming possibilities of this high value native species. Despite their abundance at one time, the mahseer population has been declining in number and size in natural waters and is in serious danger of extinction. The National Commission on Agriculture (1976) in its report on fisheries had stated there was a general decline in mahseer fishery in India due to indiscriminate fishing of brood and juvenile fish and the adverse effect of the river valley projects and accordingly suggested extensive survey and detailed biological investigation on this alarming situation.

The biological investigations commenced in 1970 in Pune District of Maharashtra under the guidance of C.V. Kulkarni and eventually yielded very significant information on artificial propagation of mahseer. The downward trend in the commercial and sport fishing catches of mahseer due to various man-made and ecological factors could be obviated by a continuous stocking programme on a large scale and by strictly enforcing the prevailing legislation. This programme would require production of fry and fingerlings of this species on a very large scale and their release in depleted natural perennial waters. During the last three decades of the 20th century extensive studies on the distribution, biology and fishery of the commercially important mahseers have been made by TPCL. This has led to development of techniques of breeding, larval rearing and cultural practices at TPCL hatchery farm Lonavla, which is now capable of producing fry and fingerlings of all the desired species of mahseer. The mahseer hatchery technology developed by TPCL may well lead to the revival of mahseer fisheries in Indian waters, provided standardised simple mahseer hatcheries based on TPCL technologies could be set up in the rural areas adjacent to rivers and reservoirs.

Causes of depletion. The exponential increase in human population is the root cause for the loss of biodiversity and the depletion of natural resources. Much has already been said regarding the depletion of mahseer. The major possible factors for the depletion of mahseer stocks are:

• degradation of ecological conditions of aquatic systems,

• indiscriminate fishing of broodstock and juveniles,

• impacts of river valley projects,

• industrial and human pollution,

• the use of explosives, poisons and electrofishing by poachers,

• introduction of exotic species,

• population pressures on resources.

The above- mentioned factors combined with human greed are responsible for the reckless damage to this priceless national heritage. The declining trend in the populations of mahseer needs immediate attention for its in situ conservation and rejuvenation in natural waters. The reasons for the conservation of this gene pool need no further emphasis. Several measures have been enumerated for their conservation (Kulkarni 1991; Ogale, 1997). The artificial propagation and distribution of resultant fry and fingerlings into different waters constitutes one of the most important steps to rehabilitate the species, as is being done for the well known salmon in American and European waters. However, for dependable and continued results, improved aquacultural practices for the breeding of mahseer under controlled conditions play a vital role.

The "kelah" or Golden Mahseer - takes three years to grow to a size of three kilogram! To grow to 8 kg would take some 40 years, depending on its environment and food sources. The kelah (scientific name "Tor Tombroides") which is also known as the "empurau" in Sarawak and Mahseer in India. Tor douronensis (Valenciennes, 1842), also known as blue kelah, are found in Thailand east to Vietnam and south to Indonesia. The other common name for this fish depending on the region/location it is found, are khela mahseer (or river carp) /Garing/ Semah/ Pelian - Indonesia. The kelah hijau is usually a tengas daun, a smaller sub-species of tengas, tengas can grow up to 5kg ..the biggest kelah was about 25kg ..caught in kenyir lake many many years ago. A fish of 50 kilograms is now considered a rarity with the average being more in the 5 to 10 kilogram range. Unfortunately, poachers have found Mahseer catches to be lucrative and many of the best fish end up in their traps and nets rather than on an angler's line. With large fins and a tendency to fight with rather than against the current gives Golden Mahseer the reputation of being amongst the most powerful freshwater fish. There are many stories of anglers being taken by surprise and ending up in the water with their rod, or only just saved by an attentive local guide. Other stories suggest that one of the best tactics for coping with the fishes initial run is to sprint downstream rod in hand. The kelah is one of Malaysia’s precious ecological heritage; a fish that is unique to the region. It is of very high economic value too. The prize fish which can fetch RM100 per kg, is now scarce as its population has dwindled either because of over-fishing or destruction of its habitat brought about by erosion. Anglers would have to persistent enough to trek into the upper reaches of the rivers to hunt for this game fish that foreigners call the "Malaysian Golden Mahseer". Among the places where anglers still go for the thrill of landing the fish are certain pools in the rivers of Taman Negara near Jerantut, like Sungai Tahan, Sungai Kenyam and Sungai Tembeling. Sungai Nenggiri in Gua Musang is also a haven for these much sought after freshwater fish that can fetch a good price at fine dining restaurants in the country. Sadly these Malaysian masheer (or tambriodes) faces extinction and efforts are underway to protect this endangered species. Anglers and eco-tourists are willing to pay significant sums of money to meet this fish! The kelah is essentially a carp, placed in the order of Cypriniformes, although it is loosely related to the European barbel (Barbus barbus).. It’s closer relatives are the mahseer species of India (Tor spp.) and several other countries in Asia. You could say that kelah is amember of Asia’s prime sport fishes. Kelah can be found in the mighty rivers of Malaysia: Sungai Pahang and its tributaries (Tembeling, Jelai, Tanum, Tahan, Keniam, Sat etc), S. Perak and its tributaries (Kejar, Chiong, Singor, Temengor), Sg. Muda and its tributaries (Teliang, Gawi), the rivers feeding Lake Kenyir (Petuang, Cacing, Terenggan, Tembat), Sg. Kelantan and its tributaries (Galas, nenggiri, Lebir, Aring, Pertang), The Endau-Rompin rivers (Endau, Kincin, Kemapan, Jasin, Mas, Lemakuh), and the Batang Rajang and Sg Kinabatangan systems. In fact, almost all the major rivers in the country – with the exception of Perlis – used to have stocks of this beautiful fish.
Golden Mahseer are omnivorous, feeding on plant matter and insects as juveniles and becoming more predatory as they get larger. Anglers will find a live or dead bait or a lure delivered in the bottom half of the water to work the best. Where possible, fishing from a boat is recommended as the biggest fish stay out where the current is strong. A boat also allows for a stretch of river to be covered easily - a big issue up in the mountains where the riverbanks may be very difficult to traverse.

Ikan Keli/Catfish

PENGENALAN

Ikan keli termasuk didalam keluarga Clariidae. Ia berbeza dari jenis2 ikan berduri yang lain daripada Ictaluridae saperti Ictalurus spp.(Channel catfish), keluarga Schilbeidae(Pangasidae) saperti ikan patin(Pangasius sp) dan keluarga Bagridae saperti ikan baung(Mystus sp). Dua spacies keluarga Clariidae yang biasa dikenali dinegeri ini ialah keli bunga, Clarias macrocephalus dan keli kayu, Clarias batrachus.
Ikan ini berupaya untuk hidup didalam perbagai keadaan dan mutu air. Ia hanya memerlukan kawasan ternakan yang kecil untuk diternak dan boleh distok lebih padat dari kebanyakan species lain. Ia boleh hidup diatas darat untuk beberapa jam atau didalam air yang rendah kandungan oksigen terlarut kerana ia mempunyai organ arboresen yang membolehkannya bernafas udara selagi alat pernafasan ini masih lembab.
Ikan keli eksotika/Afrika, Clarias gariepinus/lazera dan kacukan C.macrocephalus dan Clarias gariepinus telah mula diperkenalkan dari negara jiran pada tahun 1988 dan kini telah menjadi species utama ternakan dinegara kita.

Asas Ikan Keli
Ikan keli mempunyai misai yang terletak berdekatan dengan hidung. Ia berfungsi sebagai alat pengesan ketika bergerak dan mencari makanan. Ia juga mempunyai alat pernafasan tambahan yang disebut ‘arborescent organ’ yang tumbuh pada insang kedua dan keempat, sehingga ikan keli boleh bernafas menggunakan oksigen dari udara bebas. Warna tubuhnya di mana terdapat ikan keli yang berwarna perang gelap dan perang terang, malah terdapat juga yang berwarna hitam. Ketika larva baru menetas, ia berukuran sekitar 3.4mm dan lebar mulutnya lebih kurang 0.28m. Setelah ia berusia 7 hari, sirip dada akan tumbuh sepanjang 7mm dan sirip perutnya berukuran 14.9mm. Larva akan mencapai bentuk yang sempurna apabila pembesaran yang jelas di antara sirip punggung, ekor dan anus yang akan kelihatan pada hari ke-22 dan panjangnya adalah 24.4mm.
Ikan keli mempunyai sengat yang menjadikannya adalah sangat berbisa. Jika terkena sengatan ikan keli ini kesannya sedikit gatal dikawasan gigitan. Berdasarkan Weber de Beaufort(1965) ikan keli diklasifikasikan sebagai berikut;
Filum : Chordata, binatang bertulang belakang.
Kelas : Pisces, mempunyai insang
Ordo : Ostariophysi, ikan yang mempunyai tulang pada bahagian atas sebagai alat pelengkap keseimbangan.
Subordo : Siluroidae, berbentuk panjang dan tidak bersisik.
Keluarga : Clariidae, ikan yang memiliki cirri khas dengan bentuk kepala pipihbertulang keras, sirip dada dilengkapi dengan sengat sebagai senjata dan alat Bantu untuk bergerak serta memiliki alat pernafasan tambahan dimana ia boleh menghirup oksigen dari udara bebas.
Genus : Clarias
Spesis : Clarius batrachus.

Syarat – syarat kehidupan
Ikan keli hanya hidup di kawasan air tawar sahaja. Ikan keli boleh hidup di kawasan dataran rendah dan dataran tinggi hingga ketinggian 700m pada paras laut. Ikan keli dapat dipelihara di perairan rendah kandungan oksigennya seperti di dalam parit, kolam atau tempat takungan lebihan air. Ini disebabkan olet alat pernafasan tambahan yang ada pada ikan keli membolehkannya bernafas menggunakan oksigen dari udara bebas. Malah ikan ini juga tahan kepada bahan-bahan organik.

Cara hidup ikan keli
1. Ikan keli bersifat karnivor iaitu pemakan daging. Ia boleh memakan sisa-sisa dari sisa domestik dan sisa industrial. Selain itu ikan keli juga boleh memakan kotoran dan bahagian lebihan ayam seperti perut dan usus.
2. Secara semulajadi makanan ikan keli terdiri daripada mikro organisma seperti kutu air iaitu Daphnia, Cladocera dan Copepoda. Ikan keli juga memakan pelbagai jenis cacing, jentik-jentik atau siput-siput kecil. Bagi ikan keli yang dipelihara makanan seperti palet diberikan.
3. Ikan keli suka bersembunyi di dalam lubang-lubang yang terdapat di dalam perairan. Lubang tersebut bukan sahaja menjad tempat persembunyian malah sebagai tempat untuk bertelur. Ikan keli lebih gemar akan perairan bersih dan baru di mana ikan-ikan tersebut akan berkumpul di pintu kemasukan air semasa proses penukaran air kolam pemeliharaan.
4. Benteng kolam yang tinggi tidak menjadi halangan bagi ikan keli untuk keluar dari kolam kerana dengan menggunakan sengatnya, ia boleh memanjat benteng tersebut dengan mudah. Oleh itu kolam benteng yang didirikan perlulah memenuhi ciri dan syarat yang telah ditetapkan supaya ikan keli yang dipelihara tidak mudah untuk melarikan diri.

Menentukan lokasi penternakan
Lokasi penternakan yang tepat
Lokasi penternakan dikatakan tepat jika telah menepati aspek iaitu aspek social, ekonomi dan teknikal. Aspek sosial ini bermaksud menggunakan sumber yang terdapat di sekitar lokasi secara optimum. Sumber yang dimaksudkan bukan hanya dari sumber semulajadi tetapi juga sumber manusia iaitu tenaga kerja, peralatan dan bahan-bahan yang diperlukan.
Manakala aspek ekonomi pula, jarak lokasi kegiatan penternakan dengan tempat penjualan hasil adalah penting untuk dipertimbangkan. Ini juga bertujuan untuk menjamin kesegaran ikan tersebut apabila dijual kepada pengguna.
Aspek teknikal merupakan tenaga kerja yang pakar tentang ikan keli adalah diperlukan dari segi biologi, pembesaran, pencegahan haiwan pemangsa dan penyakit, penyediaan makanan dan pengumpulan.

Ternakan
Pada masa ini ternakan ikan keli dijalankan didalam sawah padi, kolam2 tanah, kolam kanvas dan tangki konkrit. Pada asasnya sistem pengeluaran ikan didalam sawah padi adalah berbentuk perangkap dimana ikan liar dari parit dan taliair atau telaga memasuki petak sawah yang ditenggelami air pada awal musim. Pengurusan petak sawah bagi menggalakan pertumbuhan plankton saperti pembajaan dan baja organik tidak dibuat. Ikan juaga tidak diberi makanan tambahan. Ikan2 yang biasa dituai ialah ikan keli kayu, Clarias batrachus, keli bunga, C.macrocephalus, ikan haruan Channa striatus dan ikan sepat, Trichogaster pectoralis. Antara halangan bagi ternakan ikan dalam sawah ialah tanaman padi dua musim yang menyebabkan tempoh tanaman yang singkat, kaedah mekanissasi intensif dan penggunaan racun perosak yang meluas.
Ternakan didalam kolam dijalankan secara semi-intensif, dimana kadar kemasukan adalah diantara 10 - 30 ekor/m2. Makanan rumusan atau perut ayam yang telah direbus serta bahan2 sampingan pertanian saperti hampas kacang soya/kelapa digunakan. Tempoh ternakan adalah 3 - 4 bulan, terutama bagi keli eksotika.
Ternakan ikan keli dalam tangki konkrit dan tangki fibreglass/kanvas semakin mendapat perhatian orang ramai, terutama bagi mereka yang tidak mempunyai kawasan yang besar. Saiz tangki konkrit digunakan berbeza2, biasanya tangki bersaiz 3m x 5m dengan kadar kemasukan lebih kurang 100/m2 digunakan.

Kuantiti dan kualiti air
Air merupakan faktor yang paling penting di dalam penternakan ikan. Kuantiti air adalah jumlah yang sedia ada dari sumbernya seperti sungai atau saluran untuk mengairi kolam. Air yang diperlukan bagi penternakan ikan keli tidak sebesar yang diperlukan bagi penternakan ikan-ikan lain seperti ikan emas. Ini disebabkan oleh alat pernafasan tambahan yang dimiliki ikan keli di mana ia boleh bernafas melalui udara bebas. Jumlah air yang diperlukan bagi penternakan ikan keli adalah 10 liter/minit.
Bagi pembenihan ikan keli, air yang paling sesuai digunakan adalah air dari telaga, sama ada telaga semulajadi mahupun telaga galian biasa.
Kualiti air adalah berbeza-beza dan mampu mempengaruhi kehidupan ikan keli. Kepelbagaian tersebut terdiri daripada sifat fizikal, kimia dan biologi air.
Sifat fizikal air meliputi suhu, kekeruhan dan warna air.
Sifat kimia air adalah kandungan oksigen(O2), karbon dioksida(CO2), pH (nilai keasidan), ammonia (NH3) dan alkali.
Sifat biologi air pula merangkumi jenis dan jumlah haiwan akuatik( mikroorganisma) seperti plankton, sebagai contohnya yang hidup di sesuatu kawasan perairan.
Suhu air mempengaruhi kelarutan oksigen dan nitrogen di dalam air pada tekanan 1 atm(atmosfera).
Kadar larutan oksigen dan nitrogen dengan air pada tekanan 1 atm.

Struktur tanah
Tanah merupakan faktor utama dalam pembuatan kolam penternakan. Tanah yang baik akan menghasilkan kolam yang kukuh terutamanya pada bahagian permatang dan sempadannya. Permatang yang kukuh dapat menahan tekanan air dan tidak mudah pecah. Kolam yang baik tidak cepat kering dan mempunyai daya penyerapan yang rendah.
Tanah yang sesuai dan baik untuk pembinaan kolam adalah tanah liat dan tanah berpasir dengan nisbah 3:2. Tanah dengan struktur seperti ini mudah dibentuk dan tidak mudah pecah.

Penternakan makanan semulajadi ikan keli
Kutu air atau Daphnia sp. Merupakan salah satu makanan bagi ikan keli. Ia boleh diperolehi secara semulajadi malahan ia juga boleh dikulturkan atau diternak. Tidak sukar untuk mendapatkan kutu air kerana ia berada dimana sahaja walaupun di dalam parit atau longkang.
Penternakan kutu air dilakukan di dalam kolam atau fiberglass yang berukuran 1m x 1m x 0.25m.
Kolam untuk penternakan kutu air, berukuran 1m x 1m x 0.25m. Bagi tujuan untuk mempercepatkan pertumbuhan kutu air dan harus dibaja dengan najis ayam.

Atau disesuaikan dengan keluasan tanah.
1. Mula-mula kolam dikeringkan dan dibersihkan kemudian ia disikan dengan air bersih.
2. Bagi mempercepatkan proses pertumbuhan kutu air, pembajaan harus dilakukan dengan menggunakan najis ayam yang telah kering sebanyak 2-5 gram/liter air.

Cara penternakannya adalah dengan ;
1. Menggunakan alat penapis supaya bahan-bahan yang kasar dapat diasingkan dan tidak masuk ke dalam kolam.
2. Perubahan pada warna air kolam kepada warna perang seperti air teh menandakan penternakan adalah baik.
3. Air tersebut dibiarkan selama 3-4 hari.
4. Pada hari kelima, bibit-bibit Daphinia akan terhasil. Ia akan tumbuh dengan cepat dan mencapai puncaknya pada hari ketujuh. Ketika itulah kutu air diambil untuk diberikan kepada benih ikan keli menggunakan jaring halus yang berukuran 1.5- 2 mm.
5. Penternakan kutu air di dalam kolam diulangi dengan dos ½ dari jumlah penternakan pertama bagi memastikan pertumbuhan kutu air yang berterusan. Proses ini dilakukan 7-8 hari sekali.

Pembenihan
Teknik pembenihan ikan keli tempatan tidak sama dengan ikan keli eksotika. Ikan keli tempatan di perairan umum membiak secara semulajadi dengan meletakkan telurnya di dalam sarang. Lubang-lubang permatang adalah sarang yang dibuat oleh ikan keli. Selain itu, ikan keli juga bersarang di bawah benda-benda yang tenggelam di dalam air seperti batu atau kayu.
Melalui konsep diatas para penternak mencuba mengusahakan penternakan ikan keli dengan menyediakan potongan-potongan buluh dan disimpan di dalam kolam.
Kaedah ini tidak berkesan. Ikan keli tidak bertelur pada potongan-potongan buluh yang disimpan di dasar kolam tetapi hanya pada bahagian berbentuk sarang atau kotak-kotak yang dipasang di tepi atau dipinggir permatang.
Teknik Pembenihan
Teknik pembenihan yang biasa dipraktik oleh para penternak adalah dengan 2 sistem iaitu sistem pembenihan secara berpasangan dan sistem pembenihan secara rawak.

Sistem pembenihan secara berpasangan
Induk yang dipilih adalah yang sudah cukup matang. Sepasang induk matang yang disenyawakan akan ditempatkan di dalam sebuah kolam yang kecil untuk proses persenyawaan.
Kolam yang digunakan adalah kolam tembok berukuran kira-kira 2m x 1m x 0.5m. Salah satu sudut kolam tersebut diletakkan sarang yang merupakan batu bata untuk ikan keli bertelur
Ukuran sarang adalah 30cm x 40cm x 20cm. Sebuah lubang atau pintu selebar 10cm disediakan pada bahagian hadapan sarang sebagai tempat keluar masuk ikan keli. Di dalam sarang tersebut diletakkan sabut di seluruh permukaan dasar sarang.

Sebelum proses persenyawaan dilakukan, kolam akan dikeringkan dan dibersihkan unutk membunuh kuman-kuman penyakit. Seterusnya kolam diisikan dengan air bersih dan jernih pada kedalaman 15-20 cm. Induk yang ingin disenyawakan dipilih daripada sepasang ikan keli matang (jantan dan betina) di mana berat masing-masing adalah sama atau hampir sama. Induk dimasukkan pada waktu pagi di mana persenyawaan biasa berlaku pada waktu malam. Ini telah terbukti di mana pada pagi keesokan harinya terdapat telur-telur yang terhasil dan terlekat pada sabut sarang. Telur-telur tersebut akan dijaga oleh kedua-dua induknya secara bergilir-gilir.

Telur yang terhasil akan menetas selepas tiga hari. Pada hari keempat, benih yang baru menetas akan diberi makanan tambahan yang merupakan kutu air atau cacing sutera. Induk jantan dan betina akan ditangkap dan dipindahkan kekolam pemeliharaan induk, setelah benih berusia 7 hari. Benih akan dipelihara selama 3 minggu di kolam persenyawaan kemudian akan dipindahkan ke tempat pemeliharaan.

Sistem Pembenihan secara rawak
Bagi sistem ini, kolam pemeliharaan induk berfungsi sebagai kolam persenyawaan. Dipinggir kolam diletakkan kotak-kotak sebagai tempat persenyawaan. Kotak tersebut dibuat daripada tembok atau bancuhan simen dengan ukuran 50cm x 50cm x 60cm. Sebuah lubang sebesar 15cm disediakan pada bahagian dalam kotak tersebut sebagai tempat perlindungan keluar masuk ikan keli. Pada dinding bahagian belakang dibuat lubang untuk mengeringkan atau menangkap benih yang terhasil. Di dalam kotak tersebut dilapisi dengan sabut supaya benih akan terlekat padanya. Pada bahagian atas kotak mestilah ditutup agar keadaan gelap kerana ikan keli lebih gemar bertelur dalam keadaan gelap. Jarak antara kotak persenyawaan adalah 100cm.

Sepasang ikan keli akan diletakkan di dalam kolam seluas kira-kira 4m2. Penebaran induk dilakukan pada waktu pagi dan petang. Induk yang ingin disenyawakan haruslah dibekalkan dengan makanan berkhasiat seperti pellet atau makanana tambahan yang lain. Induk ikan keli yang sudah matang akan mencari sendiri pasanganya. Jika ikan keli telah menemui pasangannya, induk akan mencari kotak atau sarang yang dikehendaki. Kemuadian induk akan menjalani proses persenyawaan di dalam kotak di mana induk betina akan melepaskan telur manakala induk jantan akan mengeluarkan spermanya. Telur-telur yang hasil persenyawaan akan melekat pada sabut yang diletakkan di dalam sarang.

Telur akan menetas setelah tiga hari disenyawakan dan pada hari keempat ia akan diberi makanan yang terdiri daripada kutu air atau cacing sutera. Setelah seminggu, benih ikan keli bolehlah dipindahkan menggunakan jaring halus untuk dipelihara di tempat lain.

Pembenihan secara akuakultur
Kaedah pembenihan secara kultur, benih ikan keli yang dihasilkan akan bertahan lebih lama dan risiko kematian adalah kurang jika dibandingkan dengan kaedah tradisional atau semi-intensif. Kegiatan pembenihan secara intensif meliputi penyediaan calon induk, pemilihan induk yang matang dan penyediaan kolam yang digunakanuntuk persenyawaan. Bagi mendapatkan hasil yang maksima, setiap kegiatan haruslah dijalankan mengikut prosedur yang telah ditetapkan.

Induk
Penyediaan induk yang baik bergantung kepada pengetahuan tentang ciri-ciri yang terdapat pada setiap induk jantan dan betina. Induk yang baik memiliki ciri-ciri seperti berikut;
1. Induk betina
- Kepala lebih kecil, mulut membulat, perut lebar, berbentuk tubuh yang mantap
dan tidak cacat .
- Beratnya mencapai 150-250 gram apabila berumur melebihi satu tahun.
- Induk bukan dari jenis yang sama.
- Induk memiliki tindak balas terhadap makanan, tahan kepada penyakit dan cepat sembuh.
2. Induk jantan
- Bentuk tubuh yang mantap, mulut membulat, berwarna cerah dan tidak
cacat.
- Pada umur minima satu tahun boleh mencapai berat diantara 150-250gram.
- Induk bukan dari jenis yang sama.
- Induk memiliki tidak balas terhadap makanan, tahan kepada penyakit dan cepat sembuh.

Terdapat beberapa perkara yang perlu dipertimbangkan sebelum memelihara induk ikan keli. Diantaranya adalah;
1. Kepadatan penebaran.
2. Jenis dan jumlah makanan yang diberikan.
3. Kolam yang digunakan biasanya merupakan kolam yang menjadikan tanah sebagai dasarnya berukuran 20m x 10m 1m.
4. Kolam mestilah dikeringkan dan diairi semula.
5. Menternak kutu air. Kolam perlu dibaja dengan menggunakan najis ayam sebanyak 200gram/m2 seterusnya diletakkan kapur pertanian sebanyak 50gram/m2 . Kapur ini bertujuan untuk membunuh kuman-kuman penyebab penyakit yang terdapat di dalam kolam tersebut.
6. Kolam disikan dengan air setinggi 60-80cm dari dasar kolam. Sebanyak 10-15 ekor/ m2 induk ikan keli dimasukkan ke dalam kolam di mana berat induk adalah diantara 50-100gram seekor. Semasa proses pemeliharaan, induk diberi makanan tambahan seperti palet dengan kadar;
1. Protein ..............32-35%
2. Lemak ...............7-8%
3. Karbohidrat.......30%
4. Vitamin..............1-2%
Jumlah makanan yang diberikan sehari adalah 3% daripada berat ikan tersebut dengan kekerapan 3 kali sehari;
1. Pagi
2. Petang
3. Malam
Pemeliharaan dilakukan selama 2-3 bulan. Pada masa ia boleh dipindahkan, berat ikan keli boleh mencapai 150gram seekor.

Pemeliharaan Induk
Induk jantan dan betina dipelihara secara berasingan di dalam kolam yang mempunyai batas. Luas kolam pemeliharaan adalah sekitar 40-50 m2 . Kolam yang hendak digunakan perlulah dikeringkan selama 3-4 hari unutk membunuh kuman-kuman penyakit dan memudahkan pembajaan. Kolam akan dibaja dengan 200 gram/ m2 .najis ayam dan kapur sebanyak 50 gram/ m2 . Kolam disi dengan baja dengan air pada kedalaman 80-100cm. Sebanyak 3-5 ekor/m2 induk ikan keli sahaja akan dimasukkan ke dalam kolam.
Untuk mempercepatkan proses kematangan, makanan tambahan iaitu makanan buatan dan makanan alternatif. Makanan buatan merupakan pellet. Makanan tambahan alternatif yang boleh diberikan adalah anak-anak ikan atau daging siput. Makanan tambahan ini diberkan secara berselang-seli dengan makanan palet.
Indeks Kematangan Gonad Ikan keli betina( Sember rujukan : www.dof.gov.my)

Penentuan tahap kematangan gonad ini adalah berdasarkan pada perkembangan gonad, perubahan warna telur dan pengisian pada rongga perut. Penerangan bagi tahap kematangan gonad 1 hingga 4 adalah seperti berikut ;
1. TKG 1 (belum matang)
Gonad kecil dan memanjang 10-15mm, lutsinar dan butir-butir telur belum terbentuk. Jika sudah terbentuk, telur tersebut masih berwarna lutsinar
2. TKG 2 (mulai matang)
Gonad semakin membesar dan berwarna kuning. Butir-butir telur sudah mula
kelihatan dan panjangnya diantara 15-20mm.
3. TKG 3 ( matang)
Gonad lebih besar, panjang 20-30 mm, berwarna kuning keperangan. Butir-butir telur memenuhi setengah daripada ruang perut dan mula memberi tekanan terhadap alat pencernaan ke bahagian dorsal(punggung)
4. TKG 4(sangat matang)
Gonad besar dengan panjang 30-50mm, berwarna kuning keperangan dan memenuhi dua pertiga ruang perut.

Indeks Kematangan Gonad Ikan keli jantan
1. TKG 1 (belum matang)
Gonad kecil dan panjang 5-12mm, berwarna putih dan permukaan gonad mula tidak rata.
2. TKG 2 (mulai matang)
Gonad lebih besar, panjang 12-30mm, berubah kepada warna putih jernih dan mula kelihatan bentuk gerigi mula kelihatan.
3. TKG 3 ( matang)
Gonad besar dengan panjang 20-45mm dan mula memenuhi 2/3 ruang perut. Warna
jernih dan kelihatan bergerigi pada gonad semakin membesar.
4. TKG 4(matang)
Gonad bear dan panjang, memenuhi 2/3 ruang perut. Gonad mula mengembung dan berwarna jernih.

Teknik pensenyawaan
1) Teknik pensenyawaan berpasangan di dalam kolam
i. Kolam yang digunakan seluas 1-2m2 dan sudah dikeringkan dan dibersihkan.
ii. Pintu pembuangan perlu ditutup dengan sempurna.
iii. Kolam diisikan dengan air pada kedalaman 40cm.
iv. Sabut disediakan sebagai tempat untuk benih melekat.
v. Pemilihan ikan keli yang telah matang gonad dari kolam pemeliharan induk.
vi. Waktu pensenyawaan pada waktu pagi.
vii. Pengawasan perlu dilakukan pada setiap hari bagi memastikan pensenyawaan telah berlaku atau belum.
viii. Sabut di dalam sarang tersebut perlu dipantau bagi memastikan samaada induk sudah bertelur atau belum.
ix. Tanda-tanda mengawan, terdapat telur berwarna kuning jernih pada sabut.
x. Setelah beberapa hari induk akan tetap menjaga sarangnya. Dilihat juga ikan keli yang melibaskan ekornya bagi mengekalkan kesegaran atau untuk meningkatkan kandungan oksigen di dalam air.
xi. Benih akan diberi makanan tambahan iaitu kutu air atau cacing sutera setelah masuk hari keempat.
xii. Tempoh penjagaan di kolam pensenyawaan adalah lebih kurang 2-3 minggu seterusnya benih akan dipindahkan ke tempat pemeliharaan.
2) Teknik pensenyawaan secara rawak
i. Luas kolam yang dicadangkan 15-20 m2.
ii. Kolam perlu dilengkapi dua pintu air untuk kemasukan air dan pengeluaran air.
iii. Pada pintu-pintu tersebut dipasang jaring untk mengelakkan ikan terkeluar.
iv. Sarang dibina disisi-sisi kolam sebanyak 1/3 dari jumlah induk betina. Ukuran sarang adalah 50cm x 50cm x 60cm diperbuat daripada simen.
v. Kedalaman yang diperlukan adalah 30cm. Satu lubang juga dibuat pada dinding bahagian dalam sarang untuk laluan keluar masuk ikan tersebut.
vi. Jarak antara sarang adalah 75-100cm. Selain itu, bahagian atas sarang tersebut perlulah gelap. Kolam yang hendak digunakan perlulah dikeringkan selama 3-4 hari untuk membunuh kuman-kuman penyakit dan memudahkan pembajaan. Kolam akan dibaja dengan 200 gram/ m2 najis ayam dan kapur sebanyak 50 gram/ m2 . Kolam disi dengan baja dengan air pada kedalaman 80-100cm. Sebanyak 3-5 ekor/m2 induk ikan keli sahaja akan dimasukkan ke dalam kolam.
vii. Nisbah 1jantan dan 2 betina. Induk-induk ini mestilah matang.
viii. Cara yang sesuai untuk meransang proses pensenyawaan adalah mengawal ketinggian air kolam mengikut keadaan yang sepatutnya.
ix. Telur akan menetas setelah 2-3 hari pensenyawaan berlaku.

Pemeliharaan
1. Penyediaan
1. Memudahkan pengendalian, pemeliharaan sebaik-baiknya di dalam kolam tembok. Disamping itu, kolam tersebut harus terlindung daripada cahaya matahari. Kolam perlu dilengkapi dengan pelindung tetap seperti atap genting atau plastik atau pelindung sementara seperti atap atau daun kelapa.
2. Pelindung juga melindungi kolam daripada dimasuki oleh air hujan kerana dikuatiri benih ikan akan mati akibat perubahan suhu secara mendadak.
3. Ukuran kolam pemeliharaan 5-10 m2 dan dilengkapi dengan pintu masuk dan keluar air. Kolam perlu dikeringkan 1-2 hari dan dibersihkan dari sebarang kotoran. Ketinggian air kolam tersebut adalah sekitar 20-30cm.
4. Tanaman air atau potongan – potongan buluh juga diletakkan di dalam kolam kerana ikan keli amat gemar kepada kawasan yang gelap sebagai tempat berlindung.

2. Penebaran
1. Penebaran benih lebih sesuai dilakukan pada waktu pagi atau pada suhu yang masih rendah untuk mengelakkan tekanan pada benih tersebut.
2. Benih adalah berasal dari hasil proses pensenyawaan.
3. Jika benih dari tempat lain, ia perlu dibiasakan dahulu dengan keadaan yang baru sebelum dilepaskan ke dalam kolam. Caranya adalah membiarkan alat pemindah benih terapung-apung selama 5 minit di atas permukaan air kolam pemeliharaan. Kemudian air ditambahkan sedikit demi sedikit sehingga keadaannya sama dengan permukaan air di kolam pemeliharaan. Benih dibiarkan keluar dengan sendiri ke dalam kolam pemeliharaan.
4. Kepadatan penebaran adalah 150 ekor/ m3 air.

3. Teknik-teknik pemeliharaan
1. Benih akan diberi makanan tambahan yang merupakan makanan buatan berkadar protein 40% sepanjang tempoh pemeliharaan
2. Jumlah makanan yang diberi adalah 5% dari berat benih ikan keli yang dipelihara.
3. Makanan diberikan dengan cara menaburkannya keseluruhan permukaan kolam dan dilakukan 3 kali sehari pada waktu pagi, petang dan malam.
4. Kualiti air sentiasa dijaga. Jika air tidak mengalir, penggantian air perlu dilakukan dengan menggunakan tiub sifon. Kaedah ini dapat menyingkirkan kotoran yang terdapat di dalam kolam.
5. Jika pengairan air 0.04 liter/saat, tiub sifon tidak perlu digunakan.
6. Jika terdapat ikan yang diserang penyakit atau mati, benih tersebut perlu diasingkan atau dibuang dengan segera supaya penyakit tersebut tidak tersebar lalu menjangkiti ikan lain
7. Ikan keli akan dipelihara di dalam kolam pemeliharaan selama 2 bulan atau bergantung kepada keperluannya.

4. Pengumpulan
1. Setelah benih mencapai ukuran tertentu atau sudah menepati syarat, maka ia boleh dikumpul.
2. Pengumpulan dijalankan pada waktu pagi atau petang di mana suhu adalah rendah.
3. Cara pengumpulan adalah dengan mengeringkan kolam secara perlahan-lahan sehingga air tinggal disaluran tengah.
4. Benih tersebut ditangkap secara berhati-hati dengan menggunakan alat penangkap yang halus.
5. Ini bertujuan untuk mengelakkan benih daripada luka atau cacat semasa penangkapan.
6. Benih ditampung dengan alat yang sesuai atau kolam lain untuk dipelihara ditempat pembesaran atau untuk dijual.
7. Jika teknik pemeliharaannya sesuai dan benih tidak dijangkiti penyakit, tempoh pemeliharaan adalah sekitar 20%-30% dari jumlah benih dilepaskan.

Pembesaran
1. Ikan keli dijual, biasanya mempunyai berat 150-200 gram seekor atau sewaktu ikan keli berumur 6 bulan jika ia diberi makanan tambahan yang mencukupi, kualiti air yang baik dan tiada serangan penyakit dan haiwan pemangsa.
2. Ikan keli adalah lebih sesuai jika diternak di dalam kolam yang bertembok dengan dasarnya adalah tanah dan lumpur. Ini merupakan sifat semulajadi ikan keli yang suka membuat lubang pada batas dan menyukarkan untuk melihat. Tetapi keluasan kolam yang dibina haruslah tidak terlalu besar kerana dikuatiri akan menyukarkan proses penangkapan ikan keli. Luas kolam yang disyorkan adalah 20 m2.
3. Jika kaedah kanvas atau ternakan di dalam kolam pastikan ciri-ciri tempat tinggal yang sama perlu digunakan seperti kolam tanah.

Pemindahan
Pemindahan adalah proses memindahkan ikan keli dari satu tempat ke satu tempat yang lain. Pemindahan dilakukan mengikut saiz ikan keli, samada yang masih kecil iaitu benihnya sehinggalah yang berukuran besar. Sistem pemindahan ini boleh dijalankan dengan dua cara iaitu cara terbuka dan cara tertutup.
Pemindahan secara terbuka.
Kaedah ini sesuai untuk ikan keli yang berukuran besar dan sudah boleh dipasarkan. Alat yang digunakan adalah tong plastik atau kolam yang diperbuat daripada fibre glass.

Pemindahan secara tertutup
Alat yang digunakan untuk pemindahan secara tertutup ini adalah dengan menggunakan karung plastik yang mengandungi oksigen.
Faktor- faktor lain semasa proses pemindahan.
1. Teknik pemindahan
2. Alat pengangkutan
3. Tempoh dan jarak pemindahan
4. Jumlah atau ukuran ikan keli
5. Waktu pemindahan dijalankan.

Ukuran benih
Alat-alat yang diperlukan adalah tabung oksigen, getah sebagai pengikat dan baldi untuk mengisi air. Air yang digunakan perlu diendapkan selama satu hari untuk membebaskan gas-gas beracun.
Jika pemindahan secara terbuka, alat yang perlu disediakan adalah air bersih dan tong plastik dengan kapasiti 20-200 liter di mana ia bergantung kepada jumlah benih yang akan dipindahkan.
Semasa diangkut, benih tidak akan diberi makan atau dipuasakan selama beberapa jamsupaya tidak mengeluarkan kotoran semasa pemindahan. Ini bertujuan untuk mengelakkan keracunan atau kekurangan oksigen sewaktu pemindahan akibat dari kekotoran.
Ikan keli yang dipindahkan mestilah sihat, tidak cacat atau tiada sebarang luka.

Ukuran besar (jualan)
Pemindahan bagi ikan keli yang bersaiz besar iaitu 50 gram keatas bagi seekor lebih sesuai menggunakan kaedah terbuka. Disamping itu sistem terbuka, membolehkan ikan keli bernafas melalui udara bebas. Saiz tong plastik perlu disesuaikan dengan jumlah ikan keli yang akan dipindahkan serta kemudahan pengangkutan yang ada. Tong untuk memindahkan ikan keli ada dipasaran dengan kapasiti 20 liter - 200 liter.

Pencegahan haiwan pemangsa dan penyakit
1. Masalah yang sering dihadapi oleh penternak ikan adalah serangan haiwan pemangsa dan penyakit.
2. Pencegahan adalah langkah utama yang perlu dilakukan sebelum serangan haiwan pemangsa dan penyakit.

Haiwan pemangsa
Haiwan pemangsa yang biasa menyerang ikan keli datang dari udara, darat dan air. Langkah pencegahan serangan haiwan ini adalah ;
1. Kolam perlu dikeringkan dan dikapurkan sebelum digunakan. Penggunaan kapur mesti mengikut dos yang telah ditetapkan.
2. Jaring perlu dipasang pada pintu kemasukan air bagi menghalang kemasukan haiwan pemangsa ini.
3. Haiwan pemangsa yang sering menyerang ikan keli adalah ular, belut dan ikan gabus.

Kerosakan/Penyakit
Terdapat dua jenis penyakit yang menyerang ikan kelii iaitu penyakit yang menyerang bahagian dalaman tubuh seperti jantung, hati atau usus dikenali dengan istilah endotern. Kedua, penyakit yang menyerang bahagian luar tubuh ikan keli seperti sirip, dikenali dengan eksotern.
Langkah-langkah pencegahan penyakit yang dilakukan seperti berikut ;
1. Sebelum pemeliharaan, kolam perlu dikeringkan dan dikapurkan untuk membunuh kuman pembawa penyakit.
2. Kualiti air mesti sentiasa dijaga.
3. Makanan tambahan yang diberikan haruslah sesuai dengan dos yang telah ditetapkan dimana jika berlebihan akan mengganggu kualiti air.
4. Proses pengumpulan dan pengambilan mesti dilakukan dengan baik dan berhati-hati agar ikan tidak mengalami kecederaan.
5. Binatang-binatang pembawa penyakit seperti burung atau siput haruslah dihalang daripada memasuki kolam penternakan.
Didalam air, patogen(agen penyebab penyakit)mudah merebak antara ikan melalui insang dan kulit. Secara amnya, ikan yang diternak pada keadaan yang optimum akan menghalang tekanan patogen dalam air saperti bakteria, virus dan kulat. Kualiti air yang buruk, pemakanan yang kurang, pengedalian ikan secara kasar dan sekitaran yang tidak selesa boleh menggangu ikan2 ini. Ini boleh menyebabkan daya tahan badan menjadi kurang dan terdedah kepada serangan penyakit. Keadaan ini boleh serius bagi anak ikan kerana mereka masih dalam proces untuk menbina daya tahan penyakit.
Ikan keli yang mula diserang penyakit boleh dikesan dengan mata kasar melalui tanda2 seperti :
a) Warna kulit akan menjadi lebih hitam daripada biasa, warna ditepi2 sirip pula menjadi kemerahan.
b) Ikan tudak mempunyai selera makan.
c) Ikan tidak aktif dan timbul kerpemukaan dengan keadaan menegak kepada permukaan air.
d) Berenang tidak tentu arah, kadangkala berenang secara berputar.
e) Kulat didapati dimisai dan badan. Kadang2 sirip dan misai kudung.
f) Bahagian pinggangnya bengkak.
g) Luka2 dibadan dan bengkak perut.
h) Sirip reput dan rapoh.
i) Bintik2 merah diseluruh badan.

Mikrobial(Bakteria dan Virus
Keosakan yang biasa pada ikan2 keli ialah disebabkan oleh patogen dan pasit/perosak. Bakteria Aeromonas hydrophila, bakteria saprofitik yang terdapat didalam air terjadi apabila jangkitan sekunder oleh tekanan kerana kadar kepadatan yang tinggi dan makanan ikan baja yang digunakan yang menyebabkan kualiti air yang buruk. Ia boleh menyebabkan 90% kematian dikolam asuhan dan 50% didalam kolam tumbesaran.
Ikan yang berpenyakit menunjukkan tanda2 kurang selera makan, lesu, berenang perlahan2 dan kelihatan mencungap dipermukaan air bagi mendapat udara dan berada dalam keadaan tegak pada permukaan air. Kematian berlaku dalam tempoh yang singkat. Kulit ikan yang perpenyakit berwarna pudar dengan tompok merah halus disekililing perut. Bahagian abdomen kelihatan membesar dengan sirip kaudal dan reput. Rongga badan berisi dengan bendalir, buah pinggang membengkak dan hati berwarna pucat. Keadaan ini dinamakan haemorrhagic septicaemia iaitu kedapatan racun dan bakteria dalam darah. Ini bersama2 dengan Pseudomonos spp. menjadi punca utama haemorrhagic septicaemia ini. Kaedah pengawalan paling baik ialah dengan mengurangkan kedapatan ikan.

Bakteria Myxobacteria sp
Ia merupakan jangkitan sekunder, menyerang ulser yang disebabkan oleh lain2 patogen diatas permukaan air. Biasanya ia menyerang bahagian dorsal badan, kelihatan bintik putih yang meliputi ulser dan merebak kebahagian lain badan. Ikan yang dijankiti dalam keaadan tegak dengan permukaan air atau tingkah laku berenang secara mengereng. Kawalan dengan antibiotik seperti Kloramfenikol, Terramaisin atau Oksitetrasiklina sebanyak 5 - 7.5mg bahan aktif/kg makanan ikan sehari selama 5 - 15 hari.

Kulat Saprolegnia sp
Kulit ikan yang diserang oleh kulat ini kelihatan seperti diselaputi oleh bentuk2 kapas. Serangan penyakit terjadi akibat dari kecederaan pada kulit yang disebabkan oleh pengendalian, pemukatan dan serangan ektoparasit. Jangkitan yang teruk boleh menyebabkan kematian. Penyakit ini njuga menjangkiti telur dan rega. Kawalan anak ikan dan ikan besar dengan malakit hijau sebanyak 0.05 - 1.0ppm selama 24jam.

Perasit Protozoa
Parasit2 protozoa yang didapati didalam ternakan keli ialah :
a) Trichodina spp, protozoa halus yang berbentuk piring yang terdapat disekeliling insang dan permukaan luar badan dan sirip. Biasanya ia merbahaya kepada rega dan anak2 ikan.
b) Oodinium sp, Ichthyobodo(Costia)sp, Henneguya sp, Myxosoma/Myxobolus Sistanya didapati didalam organ biak ikan dan Myxidium sp didalam pundi halus dan usus.
Kaedah kawalan ialah dengan formalin dengan kadar 25 - 50ppm atau Dipterex dengan kadar 0.25ppm pada kolam.

Parasit Cacing
Gyrodactylus spp, parasit monogenea didapati dikulit2 dan dijumpai didalam bilangan yang ketara. Ia boleh menyebabkan kematian yang banyak terutama kematian yang tiba2 bagi ikan yang sihat. Ikan yang dijangkiti akan mempunyai tompok2 hitam pada badan dengan kulit yang mengelupas. Dicadangkan kawalan Dipterex dengan kadar 0.25ppm atau formalin dengan kadar 50ppm disyorkan.

Kerosakan oleh lain-lain punca
Penyakit yang bukan berpunca daripada mikrob iaitu penyakit kekurangan zat makanan atau mutu air yang teruk boleh menyebabkan kesihatan ikan tergugat, tulang kepala retak, badan bengkok/cacat, otak bahagian belakang musnah dan bengkak perut. Ikan keli kayu dan bunga adalah sangat mudah dijangkiti epizootic ulcerative syndrome(EUS). Ikan yang dijangkiti akan menunjukkan lika pada kulit dan otot serta mata yang terbonjol. Musuh2 lain ialah burung, biawak, ular, katak, ketam, ikan haruan, belut, ikan puyu dan lain-lain.

Amalan sebelum ikan distok
Sebelum ikan dimasukkan kedalam kolam untuk ternakan, perkara-perkara berikut hendaklah diamalkan:
a) Bungkusan plastik yang mengandungi benih hendaklah diremdam terlebih dahulu didalam kolam yang akan dilepaskan benih selama kira2 10minit supaya suhu air dalam bungkusan sama dengan suhu air kolam.
b) Bungkusan plastik dibuka dan air kolam dimasukkan sedikit demi sedikit kedalamnya sebelum benih dilepaskan.
c) Lepas ikan kedalam kolam tersebut.
d) Selepas 6 jam, makanan halus dan lembut boleh diberikan sedikit demi sedikit. Anak ikan boleh juga diberikan rawatan secara rendaman sebelum dimasukkan kedalam kolam dengan kaedah seperti berikut:
Formalin
Ikan dirawat dengan 25ppm formalin untuk tempoh masa yang tidak tetap(2.5ml formalin dicampur dengan 100 liter air)
Furanace atau Garam Biasa
Sebagai langkah kawalan, semasa memindahkan ikan dan sebelum memasukkan ikan disyorkan ubat Furanace(Nifurpirinol, iaitu satu derivatif nitrofuran)dibubuh dalam air dengan kadar 10mg/liter air atau larutan 5.0g garam biasa bagi setiap liter air. Rawatan ini dijalankan secara rendaman selama 1 - 3 jam.
Dipterex
Rendaman dalam 0.25ppm Dipterex selama 3 jam.

Menggunakan bahan kimia didalam air
a) Formalin, 20 - 100ppm : selama 1 jam(guna apabila suhu tinggi).
b) Dipterex, 0.25 - 0.30ppm : selama 12 jam(rawatan pada suhu tinggi dan pancaran matahari).
c) Kalium permanganat, 2 - 4.0ppm : selama 1 jam(rawatan semasa naungan)
d) Garam biasa, 1 - 3% : selama 20minit. Garam dan beberapa asid hendaklah digunakan dengan berhati2. Lendir pada badan ikan melekat pada organ pembantu pernafasan. Ia akan menghasilkan sebatian yang membahayakan ikan.

Menggunakan bahan kimia didalam air atau makanan dilakukan dengan:
1) Melarutkan 1mg antibiotik kedalam 1 - 2 liter air atau,
2) Mencampurkan 5.0 - 7.5mg antibiotik kedalam 1kg makanan. Antibiotik adalah bahan yang didapati daripada mikro-organisma seperti kulat dan bakteria dimana ia berupaya menahan pembiakan mikro-organisma serta membunuhnya. Bagi ternakan keli, Oksitetrasiklina adalah disyorkan. Walaupun begitu adalah dinasihatkan supaya penggunaan antibiotik tidak diamalkan kerana kemungkinan kesan sampingan kepada ikan yang kita makan dan persikitaran perairan dimana kesan dari kedua2 ini mungkin menyebabkan terdapat bakteria-bakteria yang lebih rintang terhadap penyakit.

Pemakanan
Biasanya ikan-ikan didalam kurungan mengalami penyakit kekurangan zat makanan. Ini akan mengurangkan daya tahan ikan terhadap penyakit. Oleh itu, pemberian makanan yang seimbang adalah penting bagi memastikan pertumbuhan ikan yang baik.

Jenis-jenis Makanan
1) Perut Ayam : makanan ini tidak begitu digalakkan kerana ia boleh menyebabkan ikan yang diternak mengandungi banyak lemak, bau yang tidak menyenangkan dan pencemaran kolam. Jika tidak ada pilihan lain, ia boleh digunakan dengan mengurangkan kesa2 yang tidak dikehendaki itu. Caranya ialah perut hendaklah direbus dan dicincang dengan mesin pengisar sebelum diberi makan kepada ikan.
2) Campuran Ikan Baja/Dedak Padi : makanan campuran ikan baja (10%) dengan dedak padi (90%) boleh diberikan dari peringkat permulaan ternakan kesaiz pasaran. Cara lain ialah dengan menggunakan ikan baja dan 10% dedak padi sehingga jualan. Campuran makanan ini boleh diberi untuk selama dua bulan pertama, selepas itu, kadar dedak padi dinaikkan sehingga 20% dan satu bahagian beras hancur masak. Pada bulan keempat, kadar beras hancur masak ditingkatkan kepada dua bahagian.
Makanan diatas hendaklah dijadikan bentuk"paste"(belacan) dengan menggunakan mesin pengisar. Makanan diberikan sedikit demi sedikit sebanyak dua kali sehari sehingga ikan tidak lagi memakannya. Ini bagi mengelakkan pembaziran dan kemerosotan mutu air. Campuran vitamin dan garam galian adalah bagi menghasilkan campuran makanan yang bermutu.
3) Makanan Rumusan : Makanan rumusan yang mengandungi 25 - 30% protein mentah dan dihasilkan dari baha-bahan tumbuhan dan haiwan serta vitamin dan garam galian adalah disyorkan. Kelebihan penggunaan jenis makanan ini ialah ia lebih seimbang, bersih, mudah didapati dan disimpan dan kadar penukaran makanan yang cekap.

Salah satu formula untuk membuat makanan rumusan bagi ikan keli adalah seperti berikut;

Hampas ikan : 21-25%,
Hampas kacang soya : 28-34%,
Beras hancur masak : 35-44%,
Lemak haiwan : 4-5%,
Dikalsium fostat : 1.0%,
Garam : 0.75%,
Premix Garam Galian @ : 0.1%,
Premix Vitamin @@ : 0.1%,
Antibiotik @@@ : 0.05%,

# @ termasuk CaCO3, MnSO4.7H2O, ZnSO4.7H2o, CuSO4.5H2O dan FeSO4.7H2o.
Kadar bagi diet ikan diperairan panas.
#@@ mengandungi vitamin A, C dan D3 dengan jumlah yang dicadangkan bagi diet diperairan panas.
#@@@ oksitetrasiklina atau lain-lain yang dibenarkan.

Makanan yang dicadangkan hendaklah mempunyai kandungan protein mentah minimum 25-30%, minimum lemak 3%, maximum gentian 8%, maksimum abu 16%, maksimum kelembapan 12% dan minimum fosforus 1%.
Makanan diberi pada pukul 7.30pagi dan 5.00petang. Makanan diberi dengan tangan secara sedikit demi sedikit hingga ikan berhenti memakan. Kadar pemberian makanan ialah 3-12% berat badan ikan/sehari bergantung kepada tahap penerimaannya dan peringkat tumbesaran.
Kadar diatas adalah sebagai panduan. Kadar yang sebenar bergantung kepada suhu, kandungan oksigen dan kandungan ammonia didalam air serta kesihatan ikan.
Dalam keadaan biasa, adalah sukar untuk menilai keberkesanan pemakanan keli kerana kebanyakan makanan akan tenggelam kedasar. Oleh itu adalah dicadangkan makanan rumusan jenis terapung diberi kepada ikan ternakan. Ini akan memudahkan kerja mengangar jumlah makanan yang telah dimakan. Walaupun begitu, harganya adalah tinggi. Dasar kolam dikawasan pemberian makanan perlu diperiksa untuk menilai baki2 makanan yang tinggal selepas setengah jam makanan diberi. Jika ada sisa makanan, kuantiti makanan perlu dikurangkan supaya pencemaran air dapat dikurangkan disamping menjimatkan kos.

Jenis-jenis makanan tambahan
1. Terdapat dua jenis makanan yang digemari oleh ikan keli iaitu makanan semulajadi dan makanan buatan. Makanan semulajadi terdiri daripada mikro organisma hidup di dalam air seperti plankton dan makanan buatan pula adalah makanan palet buatan.
2. Alternatif lain untuk makanan ikan keli ialah anak-anak ikan dari hasil tangkapan yang tidak boleh dipasarkan, sisa buangan penternakan ayam dan ikan serta daging siput.
3. Makanan buatan seperti palet biasanya mengandungi daging dari serbuk ikan dengan kandungan protein melebihi 30%.
4. Makanan buatan dalam bentuk palet akan diberikan pada ikan keli yang sudah agak besar iaitu mencapai berat melebihi 30 gram. Palet yang besar akan dihancurkan dan diberikan kepada ikan keli yang masih kecil.

Makanan tambahan boleh diberikan kepada benih-benih ikan semasa peringkat asuhan. Jenis2 makanan tambahan yang boleh diberi ialah; Makanan rumusan dan Hampas ikan(fish meal).
Jenis makanan yang diberikan bergantung kepada faktor sama ada ia mudah didapati, mudah disediakan serta kos yang berpatutan. Walaupun begitu, makanan rumusan yang mengandungi 60% protein mentah dicadang diberikan kepada anak ikan diperingkat ini. Makanan ini diberi sehingga ikan berhenti makan. Makanan tambahan yang diperbuat daripada telur, kadar 2 biji kuning bagi 1000 ekor anak ikan pada hari pertama dan kedua adalah dicadangkan. Ia dihancurkan dan ditabur disekililing permukaan kolam. Kadar bagi makanan ikan baja yang telah dihancurkan ialah 3kg/100,000 anak ikan. Kadar ini ditinggatkan sebanyak 0.5kg bagi setiap 2-3 hari pemiliharaan. Makanan diberi sebanyak dua kali sehari iaitu pada awal pagi dan petang.

Makanan buatan
1. Makanan buatan yang dikeluarkan oleh kilang lebih mudah untuk diperoleh terutamanya di kedai-kedai yang ada menjual makanan ikan. Harganya bergantung kepada kandungan proteinnya.

Buatan kilang
Makanan yang dihasilkan oleh kilang adalah dalam bentuk palet dengan pelbagai saiz. Protein yang terkandung di dalam palet adalah berbeza-beza bergantung kepada kilang yang menghasilkannya dan jenis ikan yang digunakan. Terdapat dua jenis palet iaitu palet terapung dan palet tenggelam.
Palet terapung merupakan palet yang akan terapung diatas air jika ditaburkan ke dalam kolam manakala palet tenggelam akan jatuh ke dalam kolam.

Buatan sendiri
Peralatan yang digunakan untuk membuat palet boleh diperolehi di kedai-kedai. Selain itu bahan-bahan utama yang diperlukan ialah ;
1. Protein – Serbuk ikan, daging siput atau sisa dari penternakan.
2. Karbohidrat – Dedak halus, hampas soya
3. Mineral – Boleh diperolehi dari kedai-kedai menjual makanan ternakan.
4. Vitamin - Boleh diperolehi dari kedai-kedai menjual makanan ternakan.
Cacing juga boleh diberikan kepada ikan keli yang berusia empat hari.

Makanan alternatif
1. Sisa-sisa ternakan ikan, ayam dan daging.
2. Harga yang lebih murah dan mempunyai kandungan protein yang tinggi.

Sisa penternakan
1. Sumber-sumber ayam telah mati tetapi tidak lagi membusuk , boleh digunakan untuk dijadikan makanan ikan keli ini.
2. Ayam-ayam ini adalah lebih baik direbus dahulu sebelum diberikan kepada ikan keli ini.
3. Pemberian ayam kepada ikan-ikan perlu mengikut sukatan tertentu untuk mengelakkan kualiti air di dalam kolam terjejas.

Sisa perusahaan ikan kering
Sisa buangan perusahaan ikan kering sebagai makanan alternatif. Sisa buangan perusahaan ini adalah seperti kepala, ekor atau sirip ikan yang sudah tidak digunakan lagi. Makanan ini boleh diberi terus kepada ikan keli, malah ada juga yang mencampurkan dedak halus dan direbus sehingga separuh masak apabila telah sejuk.

Siput
Siput merupakan musuh utama penterrnakan ikan air tawar. Siput-siput yang banyak ini boleh dijadikan makanan ikan keli ini. Siput-siput ini perlu diasingkan dari cengkerangnya sebelum diberi kepada ikan keli. Kemudian, siput direbus selama beberapa minit kemudian isinya dicungkil keluar dari cengkerangnya dengan menggunakan alat yang runcing.

Pelaburan dan keuntungan pengeluaran ikan keli
Untuk menjalankan penternakan ikan keli ini, anggaran kos yang diperlukan haruslah diketahui dengan jelas bagi memperolehi pulangan yang lumayan.
Untuk memudahkan pelaksanaannya, perhitungan analisis ini perlu disesuaikan dengan tahap kegiatan yang biasa dilakukan. Analisis merangkumi proses pembenihan, pemeliharaan dan pembesaran.

Analisis proses pembenihan
Analisis proses pembenihan ikan keli dihitung untuk jangka masa pengeluaran. Proses pengeluaran ikan keli tempatan memerlukan lebih kurang 1.5 bulan yang meliputi kegiatan penyediaan, pensenyawaan, penetasan telur (4 hari), pemeliharaan benih (30 hari) dan bakinya adalah untuk pengeringan kolam pembenihan. Jumlah induk yang disenyawakan adalah sebanyak 10 pasang. Analisis yang lengkap adalah seperti berikut.

Pelaburan
1. Kemudahan
- 10 buah tangki berukuran 2m x 1m x 0.6m =RM 750.00
- Sewa kolam 1 tahun 200/10,000 x RM 500.00 =RM 40.00
- 1 set peralatan perikanan =RM 190.00
- 10 pasang induk ikan keli @ RM10.00 =RM 100.00
JUMLAH RM 1,080.00

2. Modal kerja
- 4 beg najis ayam @ RM2.00 =RM 8.00
- 2 kg baja urea @ RM1.00 =RM 2.00
- 2 kg baja TSP @ RM1.00 =RM 2.00
- 10 kg kapur pertanian @ RM0.50 =RM 5.00
- 5 liter cacing sutera @ RM2.00 =RM 10.00
- 10 kg serbuk palet @ RM3.00 =RM 30.00
- 20 kg butiran palet @ RM1.20 =RM 24.00
- 1 tenaga pekerja sambilan @ RM230.00 =RM 230.00, JUMLAH =RM 311.00
JUMLAH PELABURAN 1 + 2 =RM 1,391.00

a. Kos tetap
1. Penyusutan/Sewa kolam
- Tangki tembok 1.5/12 x RM750.00 =RM 93.75
- Sewa kolam 1.5/12 x RM500.00 =RM 62.50
- Peralatan perikanan 1.5/24 x RM190.00 =RM 25.00
- Induk ikan keli 40% x RM100.00 =RM 40.00
Jumlah =RM 221.25

2. Faedah modal
2.5 % x 1.5 bulan x RM 1380.00 =RM 51.75
Jumlah kos tetap (1+2) =RM 273.00
b. Jumlah Kos Pengeluaran
- Modal kerja =RM 311.00
- Kos tetap =RM 273.00
Jumlah =RM 584.00

c. Penjualan
- Benih ikan keli berukuran 5-8 cm 10,400 ekor @ RM0.30 =RM 3,120.00

d. Analisis
1. Keuntungan
- Penerimaan =RM 3,120.00
- Jumlah kos pengeluaran =RM 584.00
Keuntungan =RM 2,536.00
2. Aliran tunai (cash flow)
- Keuntungan =RM 2,536.00
- Kos pengurangan / sewa kolam =RM 221.25
Jumlah =RM 2,757.25
3. Tempoh bayaran balik modal (pay back peiod)
= Jumlah pelaburan X bulan
Keuntungan= RM 1391.00/RM 2604.50 X 1.5 bulan = 0.8 bulan

f. Analisis R/C dan BEP
1. Revenue cost ratio (R/C)= Penerimaan/Jumlah kos = RM 3120.00/RM 584.00 = 5.3
2. BEP
BEP = Kos tetap/1 – Kos berubah/Jumlah jualan = RM 273.00/ 1 – RM 311.00/RM 3120.00
= RM 273.00 atau = RM 273.00 / RM 0.90 = 303 ekor

Analisis proses pembesaran
a. Pelaburan
1. Kemudahan
- Sewa kolam 1 tahun 400m2 / 1000m2 x RM 500.00 =RM 75.00
- Pondok jaga 1 buah =RM 675.00
- Pengisar daging =RM 75.00
- 1 set peralatan perikanan =RM 150.00
Jumlah =RM 975.00

2. Modal kerja
- 4 beg najis ayam 2 RM 2.00 =RM 8.00
- 3 kg baja urea @ RM 0.60 =RM 1.80
- 3 kg baja TSP @ RM0.80 =RM 2.50
-18 kg kapur @ RM 0.50 =RM 7.00
- 8000 ekor benih ikan keli @ RM0.30 =RM 450.00
- 400 kg pellet @ RM1.00 =RM 400.00
- 600 kg makanan alternative (ikan rucah) @ RM0.30 =RM 180.00
- Tenaga pekerja tetap 1 org x 5 bulan x RM100.00 =RM 500.00
- Tenaga pekerja harian 6 org @ RM10.00 =RM 60.00
Jumlah= RM 1,609.30
Jumlah pelaburan (1+2)= RM 2,584.30

b. Kos tetap
1. Pengurangan / Sewa kolam
- Sewa kolam 6/12 x RM 500.00 =RM 250.00
- Pondok jaga 6/42 bulan x RM 675.00 =RM 96.00
- Pengisar daging 6/24 bulan x RM100.00 =RM 25.00
- Peralatan perikanan 6/24 bulan x RM300.00 =RM 75.00
Jumlah =RM 446.00

2. Faedah bank
25% x 6 bulan x RM 2887.00 =RM 64.61
Jumlah kos tetap (1 +2) =RM 510.61

c. Jumlah kos pengeluaran
- Modal kerja =RM 1,609.30
- Kos tetap =RM 510.61

d. Penjualan
- Ikan keli dengan berat 800kg @RM5.00 =RM 4,000.00

e. Analisis
1. Keuntungan
- Penerimaan =RM 4,000.00
- Jumlah kos pengeluaran =RM 2,119.91
Keuntungan =RM 1,880.09
2. Aliran tunai (cash flow)
- Keuntungan =RM 1,880.09
- Kos penyusutan / sewa kolam =RM 250.00
Jumlah =RM 2,130.09
3. Tempoh bayaran balik modal ( pay back period)
= Jumlah pelaburan/Keuntungan X bulan
= RM 2584.00/RM 1880.09 X 6 bulan
= 8.24 bulan

f. Analisis R/C dan BEP
1. Revenue cost ratio (R/C)
= Penerimaan/Jumlah kos
= RM 4000.00/RM 2119.91 = 1.9
2. BEP
BEP = Kos tetap/1 – Kos berubah/Jumlah jualan = RM 510.61/1 – RM 1609.30/RM 4000.00
= RM 510.61 atau RM 510.61/0.6 = RM 851

Pasaran / Kesimpulan
1. Permintaan terhadap ikan keli yang semakin meningkat telah menaikkan semangat para penternak untuk menghasilkan ikan tersebut.
2. Pasaran ikan keli tidak terbatas untuk keperluan pengguna di rumah sahaja, malah restoran dan hotel-hotel turut mendapat sambutan.
3. Pemeliharaan adalah proses penjagaan benih ikan keli yang dihasilkan dari proses pembenihan untuk dipelihara dalam jangka masa tertentu sehingga berukuran di antara 3-5 cm atau 5-8cm seekor.
4. Pembesaran pula proses pemeliharaan ikan keli yang telah melalui proses pemeliharaan untuk dijaga dalam jangka waktu tertentu sehingga ia boleh dipasarkan. Ukurannya di antara 6-12 ekor/kg. Biasanya ikan yang dipasarka adalah 6-8 ekor/kg.