5 Preparing the Pond

The last pages of the construction section presented several ways of sealing the bottom of the pond so it will hold water better. This section tells what has to be done to prepare the completed pond for the fish.

Conditioning the Pond

If the pond is an old one from which the fish have been harvested, plow it completely. Plowing turns the ground over so that it dries well. Clear the bottom of any twigs, stumps, branches, or dead fish. Any predators (snakes, frogs, etc.) must be taken out by hand or poisoned (see "Problems of Fish in Pond" for more information on this subject). Then smooth the bottom out again. When the pond is dried enough, the soil will have large cracks in it.

After the pond is plowed, cleared, and smoothed, it should be conditioned with lime.

Whether the pond is old or new, a layer of lime should be placed on the bottom of the pond. Place the lime on the pond two weeks before the water is put into the pond.

Lime conditions the soil of the pond. It is not a fertilizer, but it helps fertilizers work. It is especially important to use lime if the soil has acids in it which might harm the fish. Lime can control these acids so they are not a danger. A farmer who is not sure whether the soil of his new fish pond has acids in it -- because he had no place to get his soil tested, or because he has never farmed the land -- is always safer if he puts lime on the bottom of the pond.

Lime comes in several forms: ground limestone; agricultural lime; hydrated (builders') lime; or quicklime. Of all these types, hydrated lime is cheapest to use because it is more concentrated.

Quicklime must be used carefully: it can burn if it touches the skin and is harmful if breathed into the body. Farmers should be warned to use quicklime only with extreme care.

Lime should be put on the pond bottom at the following rates for a new pond:

Ground Limestone 1140kg per hectare

Agricultural Lime 2270kg per hectare

Hydrated Lime 114kg per hectare

Quicklime 200kg per hectare

A word about limestone: In many areas of the world, limestone can be found locally. It is a soft stone and may be ground by the farmers themselves. It is a good idea to let farmers know whether or not limestone is available locally and to help them identify it if they can not already do so.

Filling the Pond After the lime has been on the pond bottom for at least two weeks, let the water in slowly. The water should fall from the water inlet into the pond below, so that the water mixes with oxygen from the air as it falls into the pond.

The water should not go in too quickly. If the water goes in too fast, the pond bottom will get stirred up and make the water muddy.

Let the pond sit for a few days after it has been filled. Then check the quality of the water in the pond -- before adding the fish.

Fish growth depends greatly on the quality of the water used in the pond. And the quality of the water depends upon where it comes from and what kind of soil it travels over. Testing the water quality means making sure that all the factors which relate to water are right for the fish. These factors are: temperature, oxygen content, pH, turbidity, hardness, alkalinity, and nutrient availability (source of food for the fish). The farmer does not need to know these particular words to raise fish well, but he does require a working knowledge of the factors that are part of the water world in which the fish live.

TEMPERATURE

Fish are cold-blooded animals; that is, their body temperatures depend upon the temperature of the water in which they live. Every fish species has a temperature range within which it grows quickly. This is called the optimum temperature range, and it means that this fish grows best at temperatures within that range. In a fish pond, the fish should live at their optimum to grow well. However, since fish have different temperature requirements, the farmer must choose the fish which will grow best in the temperature range of his pond.

Here are some of the common pond fish and their temperature ranges:

Genus, species Common name Temperature [degree C]

Tilapia mossambica tilapia 25-35

Osphronemus goramy gourami 24-28

Puntius javanicus tawes 25-33

Cyprinus Carpio common carp 20-25

Ctenopharyngodon idellus grass carp 25-30

Anguilla japonica eel 20-28

This chart shows that all the fish on this list could live in water that is 25 [degrees] C (77 [degrees] F). The chart also shows that an eel can live and grow well at 20 [degrees] C, but that the tilapia and the grass carp will not do well at 20 [degrees C] because this temperature is below the range in which they are comfortable. When the temperature goes higher or lower than this optimum, fish will not grow. Eventually, if the temperature goes too high or too low, the fish will die.

The farmer must watch the temperature in the pond water carefully, especially if the weather becomes unusually hot or cold. If it is possible, it is a good idea for a farmer to use a thermometer to find the temperature of his pond water. This can be done by using a thermometer which is used for taking temperatures when people are sick. The most important step is to guide the farmer to stock fish which will do well in the normal temperature ranges of his area. Then the temperature of the water will not generally be a problem, except in cases of unusual weather.

Some experienced fish growers can judge the water temperature by putting their arms in the water. Most people cannot tell temperature this way. But if the right kind of fish has been chosen for the pond, the farmer need only watch the fish to be able to judge the temperature of the pond water. If the water is becoming too hot, the fish will not eat and will move very slowly.

If the farmer sees this behavior in his fish pond, he can take out some of the pond water and put in new, cooler water. Another way of protecting the water from getting too hot is to find a way to shade the pond, so that the sun does not shine directly on the water. The shading should be temporary because sunlight is important to the success of the pond.

The picture above shows a fish pond being shaded by palm tree branches stuck into the ground around the edges of the pond. As soon as the temperature of the water goes down, the branches are removed.

Temperature, however, usually does not act alone. If the fish are showing signs of distress because of hot weather, it is often a problem caused by high temperatures and low oxygen content.

OXYGEN

The farmer cannot see oxygen, so it may be hard for him to realize its importance. But it is worth taking the time to help a pond owner understand oxygen as a critical factor in the success of his fish pond. Oxygen lack is a problem which can occur at any time during fish pond operation, and there is a good chance the farmer will have to depend only upon his own knowledge of the problem and its cause to solve it immediately.

Fish, like all animals and human beings, need oxygen to breathe and, therefore, to live. Through a process called respiration, fish and human beings take in oxygen and give off carbon dioxide. Fish will not grow well when the oxygen supply is low; and if the oxygen level gets too low, they will die.

Oxygen is a gas. Human beings get the oxygen they need from the air. They cannot see it, or smell it, but without it they would die. Most fish can only get oxygen from the water in the fish pond. The farmer cannot see the oxygen in the water either, but he should realize that it must be there in sufficient quantity for the fish to live.

Oxygen troubles arise in a pond when the supply of oxygen is used up faster than oxygen is put into the pond. This happens to human beings too -- if too many people are shut into a room with no windows or airholes, the respiration of all these people uses up the oxygen. Soon, there is too much carbon dioxide in the air. The people have trouble breathing until a window is opened and fresh air containing oxygen is let in.

This is exactly what happens to fish in the fish pond. The fish are shut up in the pond, and if there is not enough oxygen entering the pond, they will have trouble breathing. And, if the problem continues, they will die.

Water contains tiny plants and animals called plankton. Most plankton are so very small that they cannot be seen without using a microscope.

The plants are phytoplankton: The animals are zooplankton:

Water also contains higher orders of vegetation. These plants are much larger than the phytoplankton.

The fish and the zooplankton use oxygen and give off carbon dioxide in respiration; the phytoplankton and higher plants use carbon dioxide and sunlight to produce oxygen during a process called photosynthesis.

The oxygen in a fish pond also is used up by the process of decay. Dead organic matter -- leaves, fish, other plant and animal material present in the pond, use up oxygen in the decay process called oxidation. Oxidation and respiration go on both day and night, while photosynthesis can take place only during sunlight hours.

Therefore, there are times during the day when the oxygen levels in the pond can be very low, and oxygen may have to be added to the water. Oxygen can be added to the pond water by taking out some of the old water which is low in oxygen and adding new water.

The new water should be sprayed or bubbled into the pond so that the water picks up oxygen from the air as it falls into the pond.

Oxygen also can be added to pond water by:

Stirring up the water already in the pond. Some farmers beat and stir the water with poles.

Some pond owners use oars to stir the water.

Other owners run small motors to bubble the water in the pond.

In addition, winds which are strong enough to ripple the surface of the water in the pond help the air and water to mix. Remember: any disturbance of the water made by man or by nature helps put oxygen into (aerates) the water.

Life under the water is a new idea to many farmers. And it is sometimes difficult to understand that the balances which exist on land are also present in the water. Oxygen is produced and used both above and below the surface of the water. The fish pond does well only when oxygen production and oxygen use are in balanced relationship.

If the farmer understands the balance -- how oxygen is added and how it is used up, he will know how to watch for trouble before it happens. For example, if the colour of the water changes from green to clear -- in a few hours or a day -- the phytoplankton are not producing enough oxygen. If the fish are at the surface of the water and seem to be gulping air, they may need oxygen. Early in the morning, before the sun comes up, or a long period of no sunshine can be bad times because the phytoplankton need the sun to produce oxygen. Long periods of hot weather can create oxygen problems because the pond water gets warmer, and ways water cannot hold as much oxygen as cool water can.

The following table shows the difference in oxygen levels at various points in the day. For example, at 6 am, the temperature has remained steady, but the dissolved oxygen level has dropped to 6.3mg. At 6 pm, after a sunny day, the dissolved oxygen level is 16.3mg.

This table also shows that on a typical day a pond's temperature does not vary greatly. This illustrates why oxygen as a separate factor is much more important than is temperature.

MEASURED OXYGEN CONTENT COMPARED WITH TEMPERATURE IN ONE POND

Time of Day Temperature [degree] C Dissolved Oxygen, mg/1

2 am 29 9.8

6 am 29 6.3

10 am 29 6.7

2 pm 30 9.4

6 pm 29 16.3

10 pm 29 10.7

Oxygen is measured in either milligrams per litre (mg/l) or parts per million (ppm). One milligram per litre of oxygen means that there is one milligram of oxygen dissolved in one litre of water. One part per million is approximately equivalent to one milligram per litre.

Fish begin to be stressed when the oxygen-level falls below 4mg/l. For best growth, the oxygen levels should be above 5mg/l, but not more than 15mg/l. Above this level of oxygen, supersaturation often results (too much oxygen).

Sometimes, if there is a lot of sun and a lot of wind activity at the same time, and if the temperature is low, the water can become supersaturated with oxygen. Supersaturated water contains more oxygen than water can normally hold at a given temperature; it is a temporary condition. This condition can place stress on the fish. However, it does not happen very often in small ponds because the wind is not usually able to aerate pond water as thoroughly as it can in a large pond.

To determine the exact oxygen content of a pond, certain chemicals and equipment are needed. Dissolved oxygen is usually determined in the labouratory by the Winkler Method. Now, however, there are field kits available ((Hach, LaMotte). These kits are, however, expensive, and certainly will not be available to most farmers.

pH, HARDNESS, AND ALKALINITY

These three factors are not the same thing -- each one is a measure of a certain characteristic or characteristics of the water in a fish pond. Each of these factors can be measured exactly if samples of pond water can be taken to a labouratory to be analyzed, or if chemicals are available for testing the water in the field. Certainly if such testing is possible, it should be done.

However, many pond owners are not able to get their water tested and they do not have the right chemicals and equipment to do the tests themselves. For these people, it is best to stress the importance of using lime in their ponds. Lime is the proper treatment to correct imbalances in these factors, each of which is discussed in some detail here.

pH. pH is the measure of hydrogen ions ([H.sup.+]) in the water and is measured on a scale of 1 to 14. If the pH is between 0 and 7, the water is considered to be acid. If the pH is at 7, the water is neutral (not acid or basic). A pH of 7 to 14 means the water is basic. Fish grow best in a pH of between 6.5 and 9.0. Fish are very sensitive to low pH, or, in other words, to water which is acid. Most pond fish will die if the pH falls below 4 for a very long period of time.

Sometimes the pH of a pond can change quickly. For example, a heavy rain may carry acid from the soil in the dikes into the pond water. The best way to get the pH back to neutral is to add limestone (calcium carbonate) to the water by spreading it on the pond bottom or on the surface of the water. A fish like tilapia can tolerate pH from 3.7 to 10.5, but below a pH of 5, they are stressed and they will not eat.

Some people measure pH by tasting the water. If the water tastes sour or salty, it has too much acid in it. Another way to find out pH is to know where the water is coming from. If the water comes from a swamp, bog, or other place where the water is pretty stagnant and contains a lot of decaying material, it may be acid. Most water, however, has a pH which is very close to neutral. If the water comes from a river or lake, it is not likely to have a pH that will harm the fish. If the local fish do well in the water, the pond fish probably will do well also.

Litmus Paper. Some farm owners find out their pH by using litmus paper, or pH paper. These are thin strips of paper which have chemicals on them so that they change colour when they are placed into the water. If the water is acid, the paper will turn one colour; if the water is basic, the paper turns a different colour. The colour on the paper is compared to a colour chart which will give the pH for that colour. There are also electronic meters which measure pH, but these are expensive and not necessary in a field situation.

Hardness. Hardness is the measure of total soluble salts that are dissolved in the water. These salts, usually calcium ([Ca.sup.++]) and magnesium ([Mg.sup.++]), help the fish grow healthy bones and teeth. Also, the foods the fish eat, like the phytoplankton, need calcium and magnesium for growth. Water that contains many salts is called "hard" water; water that contains few salts is called "soft" water.

Hardness is related to the pH of the water, but unlike the pH, hardness stays constant throughout the day. Hardness can be measured in a labouratory or by using a field kit with chemicals. Hardness should be between 50 and 300ppm in the pond for best fish growth.

There are several ways a farmer can tell if he has very hard water without using chemicals. One method is to look closely at the pond walls where the water line is. If there is a white line on the wall of the pond where the water was touching the pond before the water level fell, there are salts present in the water which have dried on the pond walls. This water probably has a lot of salts. Hardness is important to fish.

Another way a farmer can tell if the water is hard is to wash his hands with it at the side of the pond. If the soap takes a long time to lather, and if the lather does not stay very long, the water is hard. If the water is soft and does not contain many salts, it lathers very easily and is hard to wash off.

If the water is too soft, the farmer can increase the hardness by adding lime to the water.

Alkalinity. Alkalinity is a measure of the acid-combining capacity of the water; or it is also called its buffering ability. Alkalinity measures the amounts of carbonates and bicarbonates in the water. These are materials which mix with acid in the water. The result of the mixing is that the acid is not as strong. Waters which have an alkalinity of 50 to 200ppm are the most productive for fish. Alkalinity, like pH and hardness, can be corrected and controlled by adding lime to the pond. The relationship among alkalinity, hardness, and pH can be summarized like this:

Low Alkalinity = Low pH = Low Hardness

REMEMBER: THESE THREE FACTORS ARE NOT THE SAME THING, BUT THEY ARE RELATED. IN FISH PONDS, ALL THREE CAN BE CONTROLLED BY ADDING LIME TO THE WATER.

TURBIDITY

urbidity is the term for the suspended dirt and other particles in water. Turbidity can be a problem, especially in shallow ponds, if the dirt and particles prevent sunlight from reaching the plankton, so that the phytoplankton cannot produce oxygen. An operating pond can be turbid if there are bottom feeders such as common carp stirring up the bottom mud. Or, turbidity can result from a water source which has a lot of silt in it.

Turbidity can be measured by just looking at the pond water. Or turbidity can be measured by using a device called the Secchi disc. The Secchi disc is also used to determine the total productivity of the pond.

A Secchi disc is about 30cm in diameter, painted white and black or just white, and has weights or heavy objects hanging on it to make it sink straight down into the water. The disc is suspended on a rope or a long piece of wire that is marked off in centimeters from the disc up. A Secchi disc can be made out of wood or metal -- as long as it will sink. The disc does not have to be very complicated. It does not have to be round, either. It can be any shape, as long as it has some white paint on it to help it be seen under the water. The disc can be made from a tin can pounded for this purpose.

When the Secchi disc goes into the water, it will sink straight down and disappear from sight at some depth. If the disc disappears at 30cm in depth, the pond is turbid. If it disappears immediately, either it is very turbid (brown in colour), or it is very fertile (productive), if green in colour.

Turbidity also can be measured without a disc, but this requires somewhat more experience. The farmer stands in the pond and sticks his arm under the water.

If his hand disappears when the water is about elbow deep, the water is not too turbid. If it disappears before the water reaches the elbow, the water is either turbid or very productive. If the entire arm from hand to shoulder can be seen under the water, it is not turbid at all, nor is it very productive (it does not contain enough fish food).

One way to clear up muddy water is to scatter twelve bales of hay per hectare around the edges of the pond. The hay will help to settle the mud and can then be removed easily from the pond edges. However, do not use this method in very hot weather, because the hay will begin to decay very quickly and will begin to use up oxygen in the pond water. If the pond water continues to have a lot of silt in it, the farmer should consider adding a siltation tank (see "Construction").

NUTRIENT AVAILABILITY

All fish require certain elements to grow and reproduce. These essential elements are: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulfur, calcium, iron, and magnesium. Some other elements called trace elements, are needed only in small amounts. If these elements are missing, or present in too small quantities, the fish will not grow well.

Fish Require a Balanced Diet of Elements

Carbon Potassuim

Hydrogen Sulfur

Oxygen Calcium

Nitrogen Iron

Phosphorus Magnesium

Plus trace elements

Fish get these elements from the pond soil, the pond water, and the food they eat. Some fish ponds lack elements that are necessary to fish. In these cases, it is necessary to add fertilizers to the water. Fertilizers are simply materials which contain the missing elements. The elements most often missing, or in short supply in fish ponds, are nitrogen (N), phosphorus (P), and potassium (K).

Fertilizers containing these missing elements are added to the fish pond to help the growth of the fish and of the plankton the fish use for food. Fertilization is discussed in the following paragraphs.

Fertilizers

Fertilizers are materials added to the pond to make the water more fertile (productive). As stated before, fertilization is sometimes necessary to help a pond provide the nutrients directly needed for fish and plankton growth. As a major food source of fish, plankton must be kept healthy and in good supply.

Fertilizer supplements the elements the pond gets from its own water and soil. This is especially necessary in ponds made in soil which has used up the nutrients once available.

A WELL-FERTILIZED POND

A pond which has a lot of phytoplankton is often a bright green colour. This colour indicates a "bloom" of algae. In a normal bloom, the Secchi disc disappears at about 30cm depth; when the Secchi disc disappears at 20-40cm, the pond is very productive and fertile. No fertilizer is needed in a pond under these conditions. Also, if the farmer places his arm in the pond and his am disappears from sight at the elbow, the pond does not need fertilizer.

There is one more condition when no fertilizer is needed. Sometimes a pond can become too fertile. If the Secchi disc disappears at only 15cm, the "bloom" is too thick. The thick layer of green blocks the sunlight from the pond and no oxygen can be made by the phytoplankton.

In this case, there is too much fertilizer, and the farmer must take off some of the thick layer of algae formed at the top of the pond and stop using fertilizer until the pond has recovered a normal fertilizer level.

WHEN TO FERTILIZE

If the Secchi disc can still be seen at 43cm, for example, or if the farmer can still see his entire arm from fingers to shoulder under the water, there is not enough plankton. And it is necessary to add fertilizer to the water in order to prepare the pond for the fish.

One other factor which determines the need for fertilizer is the quality of the soil. If the soil is very productive, the need for fertilizer is small; if the soil is not productive, the need is greater. A farmer should know that the fertilizer he uses on his fields, if he uses one, can also be used in his fish pond. The fish pond soil is often very like the soil of the fields around it.

TYPES OF FERTILIZERS

The kinds of fertilizers used in fish ponds vary greatly, depending on the amount of money which can be spent and what is available. Many fish pond owners use organic fertilizers, or fertilizers that come from living things; such as cow dung--because it is available on their farms. Some big pond owners like inorganic fertilizers, or chemicals made by man, like the superphosphates. But these chemical fertilizers are expensive and sometimes hard to get.

Choosing fertilizer can be difficult. The following paragraphs provide more detail about organic and inorganic fertilizers and some guidelines to the proper use of each.

Organic Fertilizers. Organic fertilizers can be plant or animal products, such as:

Vegetable matter. Chopped up manioc, sweet potatoes, or banana leaves, kang kong, guinea or napier grass, or other such things that have been allowed to rot for a while. The amounts of vegetable matter used as fertilizer can be as high as 5,000 kg/ha.

Liquid manure. Mostly animal urine containing uric acid, a source of nitrogen. It is washed out of buildings where animals are kept into the ponds and used in very small amounts by mixing it with other organic fertilizers, such as cow or pig manure.

Household scraps. Including garbage, grass cuttings, rice husks, and human sewage, also called "night soil".

Animal manure. Almost any kind of animal manure can be used as fertilizer, including cow, pig, duck, or chicken dung. Some manures are better fertilizers than others. The best way to use this kind of fertilizer is to make a "soup" of it in a tank by mixing it with water. Use the liquid part of the "soup" in the pond. Animal manure can also be placed in a burlap bag hung from a stake in the water. This way, the nutrients from the manure will be released slowly into the water without the manure itself clogging up the pond bottom. If this cannot be done, then pile the manure in the corners of the pond. Do not use too much manure: decaying manure uses up the oxygen in the pond -- particularly in hot, humid climates.

The best way to use these sources of fertilizer is to mix them all together in what is know as a compost pile. A compost pile is simply a pile of these organic materials which has been left to rot. As the materials decay together, they produce a substance which is a very good fertilizer. Compost piles are important: they provide the very best kind of organic fertilizer for fish ponds and, in many cases, they cost nothing.

Making a Compost Pile

For many years, compost has been made this way:

* Pile organic matter, such as leaves, straw, grass, rice husks or other plant material and household scraps about 30cm high.

* Put a layer of animal manure (chicken, cow, Pig, duck or whatever is available) on top of the first layer.

* Sprinkle ashes and lime on the manure.

* Repeat these layers of plant material, manure, ashes and lime until the pile is about 1.5m high and 1.5 m wide.

* Keep the pile moist, but do not let it get wet.

* Turn the pile every three weeks with a shovel for about 3 months.

* Use the pile in 3 months. It will have decayed and shrunk to about 1/10 of its original size.

There is now a faster way to make the compost ready to use as fertilizer.

* Make the same 1.5m x 1.5m pile of plant material, manure, and lime. This time, however, use more household garbage and animal manure. (Animal manure supplies nitrogen, an element used by plants during the decay process. A good compost mixture is about 1 shovelful of manure to 30 shovelsful of the other organic materials.)

* Mix the material well. Then cut all of it into small pieces, using a shovel, machete, scythe, etc. The pieces should be about 3 to 5cm long. Cutting the material speeds the rotting process. (If animal manure is hard to get, add some inorganic fertilizer containing nitrogen to the compost pile.)

* Turn the pile every few days. Use a shovel to keep it well-mixed. Compost piles can get too hot in the middle if they are not turned and mixed. Put a stick into the middle of the pile. Leave the stick in the pile for 3 minutes, and then pull it out. If the stick is hot, dry, or smelly, the pile must be turned so that the inside of the pile is now on the outside.

 Keep the pile moist, but not wet. Protect it from the rain. Animal urine can be used to keep the pile moist and helps add nitrogen to the pile (pig urine is best). A compost pile made in this way will be ready for use in only 3 weeks.

When ready, pile the compost in the corners of the pond and restrain it with a screen; or cover the compost with a layer of mud to hold the plant material in place so it does not float into the pond. The compost releases its nutrients into the pond water gradually.

APPLICATION RATES

Fertilizer should be applied at a rate determined by the area of your pond. Area is the length of the pond multiplied by the width. For example, if the pond is 10m wide by 20m long, it has an area of 200 square meters ([m.sup.2]). This is equivalent to 2/100 of a hectare. The measurements used for pond area are:

1 are = [100m.sup.2]

1 acre = 40 ares = [4000m.sup.2]

1 hectare = 100 ares = 2.5 acres = [10,000m.sup.2]

To fertilize a [200m.sup.2] fish pond with chicken manure, at a rate of 200 kg/ha, you must only use 4 kg as follows:

[200m.sup.2] = x : 200 (200) = X ; X = 4 kg
________ _________ _________

[10,000m.sup.2] 200 kg/ha 10,000

Most ponds are not as big as one hectare, so the farmer will have to determine his pond's area before using the manure. It will be hard for most farmers to calculate application rates in this way, but it is probably easy for you to develop some standard measures a farmer can use which are based on the average-sized pond in your area.

Often fish ponds are managed in conjunction with other animals. Stables are built right over the edge of the ponds, and the manure and urine from a certain number of animals are allowed to fall directly into the pond. This efficient system works well for fish which can use animal manure directly as food. Pigs are often used like this because pig dung makes a good food for some fish. Fish ponds which share the area with a number of ducks also show high yields of both ducks and fish.

For the first fertilizer added to a new pond, some common rates of application of animal manures are:

Cow dung 1000 kg/ha

Pig dung 568 - 1704 kg/ha

Chicken dung 114 - 228 kg/ha

REMEMBER:

Except for compost fertilizer, only one kind of fertilizer is needed at one time in a pond. Only use one of the application rates each time the pond is fertilized, or a combination of fertilizers with different rates to make up one rate. That is, you can use 1000 kg/ha of cow dung, or 500 kg/ha cow and 171 kg/ha chicken dung, or about 300 kg/ha cow, 57 kg/ha chicken, and 284 kg/ha of pig dung. After you fertilize keep an eye on the pond. Try not to over fertilize -- too much is just as bad as not enough.

After the first application of fertilizer, application rates do not have to be as high. Many older ponds do not need as much fertilizer because the natural life of a pond tends towards becoming more fertile the older it gets. However, each time the fish are harvested they take part of the pond's productivity with them. That is why older ponds are still fertilized -- even though they may need less fertilizer than new ponds.

Inorganic Fertilizers. Inorganic fertilizers are chemical fertilizers that dissolve in the pond water and provide their nutrients immediately. Originally, inorganic fertilizers supplied nitrogen, phosphorus, and potassium, and they were called the NPK fertilizers. Some typical NPK fertilizers were8-8-2 (NPK) and 20-20-5 (NPK). This simply referred to the mix of fertilizer that each bag supplied; for example, 8 measures of nitrogen, 8 measures of phosphorus and 2 measures of potassium. Recent studies show that if enough phosphorus is available, the plants in the pond produce their own nitrogen, and that potassium is present already in small amounts in fish. Presently, the only element needed by fish that may be lacking in the fish pond is the element phosphorus.

Now, the most common inorganic fertilizers used in fish ponds are the phosphorus fertilizers -- basic slag, powdered single superphosphate, granular double superphosphate and triple superphosphate. Some of these fertilizers can last as long as three years in the pond, so even though they are expensive initially, they are often used in fish ponds. Research shows that the best fish growth occurs when phosphate fertilizers and organic fertilizers are used together.

Application rates of phosphate fertilizers are:

Basic slag 25-30 kg/ha

Single superphosphate 114 kg/ha

Granular double superphosphate 57 kg/ha

Fertilizers have one purpose--to provide better growth of fish in ponds. Many organic and inorganic fertilizers are good. Watch the pond carefully for signs concerning a need for fertilizer. As long as the water is a green colour, the pond is in good condition. Remember: it is always best to do two things at once--wherever possible use fertilizers which can be used as food by the fish.

Now that the pond has been filled, the quality of the water tested, and the fertilizer added, the last step in preparing for the fish is to make sure that the food supply in the pond is sufficient for the fish that will be put into the pond.

Foods

It is important to be sure that fish have good food. Feeding and fertilization work together to make the pond successful.

The growth of fish in ponds is directly related to the amount of food available in the pond. The pond must provide all the food and nutrients fish need. But all fish do not need the same kinds of food: different species eat different types of food, and fish eat different foods depending on the stage of their life cycle.

Newly-hatched fry eat from their yolk sacs until the sacs are gone. The fry then eat the smallest phytoplankton in the pond. As the fry get bigger, they can eat bigger foods. Adult fish eat the things that their particular kind of fish enjoy--plankton, higher plants, worms, insect larvae, etc.

TYPES OF FISH FOOD

Fish foods can be natural (those found naturally in the pond) or supplementary (those foods added to the pond).

Natural Foods. These foods are the phytoplankton, zooplankton, detritus, snails, worms, insects and insect larvae, small plants like duckweeds and various other weeds and grasses that can be found in a fish pond. (See illustrations of Natural Foods at the end of this section.) Also, if the fish is carnivorous and eats the flesh of other animals, small fish are a food source.

Some fish eat all these foods; some prefer only one kind of food. Often a fish will choose one kind of food over another, even though either of the foods would be eaten by the fish if the other food were not available. Natural foods are the best foods for fish. The farmer should encourage, as much as possible, the growth of these natural foods--through maintaining the quality of his water, proper fertilization of the pond bottom and the water, etc.

Sometimes, however, the farmer must add food to the pond because the pond is not producing enough food for good growth. The best supplementary foods a farmer can put into the pond are extra natural foods. But there are a great number of other foods which fish will eat.

Supplementary Foods. Almost anything can be used as a supplementary food, depending on the fish species in the pond. Typical supplementary foods are: bread crumbs, rice bran, fish meal, ground-up maize, broken rice, soy bean cakes, peanut cakes, corn meal, cottonseed oil cakes, oats, barley, rye, potatoes, coconut cakes, sweet potatoes, guinea grass, napier grass, kang kong, manioc, water hyacinth, wheat, silkworm pupae, and left-over animal feeds and some animal manures.

As stated previously, the kind of extra food depends on the kind of fish. Tilapia, for example, will eat almost anything, including the supplementary foods listed above. This is one reason why they, are such very good pond fish. The silver carp, on the other hand, will eat only phytoplankton, even when it is a fish of marketable size. The farmer must know what his fish will accept before he puts the fish into the pond.

NOTE TO DEVELOPMENT WORKERS

Some of these supplemental foods are better at encouraging growth than others. The value of each food is measured in terms of how quickly and well it can help the fish gain weight. The amount of a food that can be converted into fish flesh by the fish is called the conversion ratio. And because these foods are given to help the fish grow, each food has what is known in various places as a growth co-efficient, food quotient, or its nutritive ratio.

The food quotient is figured by dividing the total weight of the food by the total increase in weight gained by the fish over a period of time. This is done as follows:

Food Quotient = weight of food given

__________________________

increase in weight of fish

For example, a fish weighing 100g is fed a supplementary food at a rate of 5% of his body weight, or 5g per day. The fish weighs 160g at the end of a 30-day period. Therefore, the food quotient of this particular food is:

Food Quotient = 5g (30 days) = 150
____________ ___

(160-100g) 60

Food Quotient = 2.5

In other words, the fish has been able to use about 2.5g of food to gain 1.0g of weight a day. This is a good conversion ratio.

The table shown here lists food quotients of some kinds of supplementary foods used with common carp. The lower the value of the quotient, the better the food was used by the fish. For example, dried silkworm pupae help the fish grow faster than do fresh silkworm pupae. REMEMBER: the conversion of foods depends upon the ability of the individual fish to use the food given to it. And that ability differs according to species.

FOOD QUOTIENTS OF COMMON CARP FEEDS

FOOD FOOD QUOTIENT

Fresh silkworm pupae 5.0 - 5.5
Dried silkworm pupae 1.3 - 2.1
Chironomids 2.3 - 4.4
Fish meal 1.5 - 3.0
Rice bran 5.1
Soy bean cake 2.2
Clam meat 1.3
Cottonseed cake 3.0
Dehydrated blood 1.5 - 1.7
Maize 4.0 - 6.0

Source: Bardach, et. al., Aquaculture

It will be hard or impossible for many farmers in your area to figure these ratios and quotients. For the farmer who is new to the effort and has few resources, it may be a good idea to direct him to the supplementary foods having the best conversion ratios for his fish.