6 Managing the Pond

It should be clear by now that much of the success of a fish pond depends upon careful planning. Before the farmer could build the pond, it was necessary for him to think through why he wanted the pond -- for food, profit, or both, what kind of ponds he could build on his land and what kind or kinds of fish are best suited to his climate and pond conditions. Only when all these factors were thought out could the pond be built. Now, with the pond constructed, fertilized, and otherwise prepared for the fish, the farmer is ready to put the fish into (stock) the ponds and get to the business of raising fish.  

Stocking

Stocking is the word used to describe the act of placing the fish (stock) into the pond. The stocking density is used here to refer to the total number of fish which can be put into (stocked) in a pond.

The stocking rate is the term used to refer to the number of one species which are put into a pond. Therefore, in a monoculture pond, the stocking rate is the same as the stocking density because there is only one kind of fish.

In a polyculture of Chinese carp, however, the stocking density, or the total number of fingerlings, may be 20,000 per hectare. Of this total, the stocking rate looks like this: grass carp are stocked at a rate of 5,000; 5,000 are bighead carp; 10,000 are silver carp.

Stocking rate and density are important. There is only enough food and room in a pond for a certain number of fish. The good growth of fish depends upon putting the right number of fish into the pond.

The age of the fish must also be considered when stocking ponds. For example, more fingerlings can be placed in a pond than brood fish, because fingerlings require less food per fish than brood fish. If the food available in the pond is not supplemented, proper stocking rates and densities are even more important.

STOCKING DENSITIES

The farmer must know how many fish he can put into his pond so that he can get the right number--either from the market or from a local stream or lake. He should remember, when he decides upon this number, that some of the fish will die--both when they are put into the pond and later. The following paragraphs provide some guidelines to use when stocking a pond with some of the more common pond fish.

Common Carp. Stocking densities differ with the age and size of the fish. In general, the more volume of water a carp has, the better is its growth. This assumes that the pond contains enough food, and the water temperature is right. The best growth of common carp has been shown with stocking densities of about 10,000 to 20,000 fish per hectare; more with fry; less with post-fingerlings. Some ponds use running water, and in these ponds, they have been able to stock up to 850,000 fry per hectare with only a 20% mortality rate.

Tilapia. Tilapia have been stocked in amounts ranging from 1000 fish per hectare to about 50,000 fish per hectare when supplementary food was provided. But stocking densities really depend on the rates of reproduction of tilapia, and whether they can be separated by sex or not.

Chinese Carp. In general, the stocking rates can only be found by trial and error, and often will be different from time to time, depending upon the availability of fry. In Malaysia, a ratio of carp stocking has been suggested of 2:1:1:3 for grass carp, bighead, silver carp and common carp. This means that if there were a stocking density of 7 Chinese carp, 2 fish would be grass carp, 3 would be common carp, and there would be only one each of bighead and silver carp. This is a good stocking rate for this density. The density for a given pond has to be figured in terms of what the pond can support.

Indian Carp. Stocking densities of Indian carp are not widely known. Some densities range from 4,000 to 11,000 fry or fingerlings per hectare, but again, the density depends upon the amount of food available to the fish.

When stocking ponds to produce market-size fish, remember that the more fish stocked, the more food must be available for the best possible growth in ponds.

The following paragraphs describe the proper methods for carrying new stock from the market or river to the pond, and for placing them into the pond.

STOCKING FISH IN PONDS

There are some general rules which apply when bringing fish from one place to another:

* do not handle the fish too much

* make sure the fish get enough oxygen

* keep the fish from getting too warm or too cold

* stock or transfer fish in the early morning when temperatures are lower and the fish are less active.

If fish are stocked so that there is enough oxygen, no temperature difference between the stocking water and the pond water, and they are not touched, the fish will not be stressed and will survive the stocking. Here are more details concerning the stocking of fish at different stages in the life cycle.

When fry are being moved for a short distance only, for example, from a nursery pond to a rearing pond, they usually are carried in small plastic or metal tubs, or in baskets.

To move fry successfully:

* Scoop the fry out of the river or pond in jars, cups, or small nets.

* Put the fry into a bucket of water.

* Carry the bucket to the pond where the fry will be placed.

* Check the temperature of the water in the bucket; it should be the same temperature as the water in the pond where the fry will be stocked.

* Add water from the pond to the bucket slowly -- until the temperature of the water in the bucket is the same as the temperature of the water in the pond.

* Tip the bucket slowly into the pond, and let the fry swim out into the pond themselves.

REMEMBER: SOME FRY WILL DIE EVEN WHEN HANDLED VERY CAREFULLY. THIS IS TO BE EXPECTED.

Moving Fry for Longer Distances.

If the fry are to be taken from a market or river which requires a few hours travel or a long distance, they must be protected better. One method, which can also be used for fingerlings (and some small adult fish), is to:

* Place fry into plastic bags filled 1/3 with water.

* Fill the rest of the bag with oxygen. The oxygen is put into the bag with a hose placed directly into the water so that the oxygen bubbles into the water.

* Tie the bag tightly so that the oxygen does not leak out.

* Place the plastic bags into tin boxes or cardboard boxes or in woven grass bags. These containers give added protection.

* Change the water in the bags after 6 hours. The oxygen will last only that long.

* Make sure the bags do not get too hot and that the temperature of the water in the bags stays at about the same temperature as the water from which the fingerlings or fry were taken.

* Place the bags in the pond unopened until the water temperature inside the bags is about the same as the temperature in the pond.

* Open the bags and let some pond water in.

* Let the bag fill up slowly, and the fish will swim out into the pond by themselves.

This process may take a little while, but it is far better to take the time than it is to lose the fry. NEVER POUR FRY INTO A POND. This will shock them and kill them all.

Stocking Fingerlings. Fingerlings are stocked in the same way as fry. Always remember that the water in their container must be at the same temperature as the water in the pond. Then let the fingerlings swim out of the container into the pond by themselves.

DO NOT POUR FINGERLINGS INTO THE POND. They may die because of the shock of hitting the water or the sudden change of temperature. Some fingerlings will die during stocking. But usually these are the weaker fish. Careful handling will mean less loss of fingerlings, as well as fry.

Stocking Adult Fish. Adult fish are a little more difficult to stock than fry or fingerlings. First, they are large (from 0.5kg up to 3.0kg) and can injure people and themselves by jumping out of containers or ponds when they are being carried or caught. For example, Chinese carp often hurt themselves this way. This problem is controlled by placing a net of some kind on top of the container so they cannot jump out.

To move fish from one pond to another, or from a pond to a container, make a carrying cradle. Use fishnet and pieces of wood or bamboo for handles. The cradle is placed around the brood fish in the water. Then the fish can be lifted out of the water and carried to the new pond or to the container for transporting. There the cradle is released and the brood fish swims away. Brood fish must never be thrown into a pond.

Adult fish often are nervous when being taken from one place to another. Some pond owners even put a hand or a handkerchief over the fishes' eyes when they are carried. Care is necessary when handling, however: brood fish particularly are sensitive to being handled. They bruise easily if they are held tightly, and the bruises can become sites for infection.

Brood fish are often carried in tubs or drums half-filled with clean, well- oxygenated water when they must be carried a long distance. Change the water often and check the water temperature each time. If the brood fish are very active, mix a solution of 1 to 4 grams per litres of urethane in the water. This will make the fish slow and less active, so they can be moved without injury.

Routine Pond Management

After the ponds are stocked, ongoing management of the pond includes:

* feeding and fertilizing as necessary

* keeping the pond in good condition

* watching for trouble and disease

Each pond, whether it is small or large, one pond or one of several, requires supervision in the above areas. And good management requires that checks of the condition of the fish and the pond be a regular part of the pond owner's day. Guidelines for both daily and monthly general maintenance are given here. Then, since fish in ponds are treated somewhat differently depending upon their species, and their stage in the life cycle, more detail on managing fry and fingerlings and managing brood stock is given.

DAILY MANAGEMENT

Ponds and the fish in them must be taken care of every day. It is a good idea to have the pond owner follow a checklist of things to do. Daily care will greatly lessen the chance that something will go wrong in the pond.

A good checklist might look like this:

* check the pond for leaks

* clean filters

* watch fish behavior near the feeding area

* feed the fish

* add fertilizer, if necessary

* watch for predators

IMPORTANT:

Check the ponds at the same time each day. Early morning is the best time because oxygen levels in the water are lowest then, and the fish are more likely to have trouble at that time of day--if they are going to have trouble at all.

Each step on the checklist involves certain activities and is discussed in more detail here.

Checking for Leaks.

Check all walls, gates, inlets, and outlets. It is possible for a plug on a drainage pipe, for example, to work loose, or partly loose, so that water leaks from the pond. Walls made of hard-packed earth can erode (wash away), especially after heavy rains. Little leaks get larger quickly. It is important to be sure the farmer realizes that in a pond only 2m deep, for example, loss of even part of the water can create problems for the fish.

Cleaning Filters.

Again, this is very important. Any filters in the pond must be removed and cleaned of silt, leaves, or other materials that have collected in them. A dirty filter at the outlet pipe could slow down the drainage process.

Watch the Fish.

A farmer can tell much about his fish by watching them carefully. If they are swimming quickly and easily around the pond, they are well. If they are waiting near the surface, they are likely to be hungry. If they are gasping for breath at the surface of the water, there is not enough oxygen and the farmer will know he has to act quickly to aerate the water in the pond.

Feed the Fish.

Remember: in some ponds it is not necessary to feed the fish extra food. The pond can be made rich enough to fill all the food needs of the fish. However, some ponds and some fish require supplemental feeding. And, sometimes, even a pond which has provided enough food before has to have food added to it.

Supplementary foods are given by:

* spreading the food over the water's surface, as with bread crumbs and rice bran

* placing food inside a floating bamboo or rope feeding ring (which is attached to the bottom of the pond)

* pressing food into dry pellets which float in the feeding ring or fall to the bottom under the ring

Guidelines for Feeding Fish

Here are some good guidelines for feeding fish which might prove useful to the farmer:

* Always feed the fish at the same time and in the same part of the pond. The fish will learn where to go to get food. Then, when the fish come near the surface of the water, inside the feeding ring, for example, the farmer can see how well they are eating and growing.

* Do not overfeed. Give only the amount of food the fish will take at one feeding. Too much food will not get eaten, but will decay and, therefore, will use up valuable oxygen from the pond during the decaying process.

The amount of food can be found by experience. And of course, the younger the fish, the less food they will need. A farmer is wise to start with a smaller amount of a food. Then, if the fish seem to be waiting near the surface in the feeding area, he will know more food is required.

There are more exact ways to determine how much food to feed the fish. Most pond owners feed fish at the rate of 2 to 5% of body weight per day. Therefore, 100 fingerlings weighing 6g each (a total weight of 600g) would receive 5% of 600g, or 30g of food a day. One hundred fish of breeder size weighing 1kg each, (total weight 100kg) would require 5kg of food a day.

Making such measures and calculations is not possible for many farmers. Therefore, it is best that they know which foods to give, how to give them, and how to judge when the fish are or are not getting enough food.

* Feed fish only 6 days each week. This will give the fish a chance to feed on whatever food remains in the pond. Too much food can clog the gills of fish, particularly those fish who eat only very fine particles of food.

* Do not feed fish for at least one day before harvesting or breeding them. When the fish eat, they void (empty) the waste from their bodies into the water. This happens even more when the fish are stressed. The combination of food and wastes makes the water turbid and increases the stress that is already placed on fish by the breeding and harvesting processes.

* Feed the right kinds of foods. Some fish will eat almost any of the foods mentioned in the section on "Preparing the Pond." Other fish are not as easy to please. The farmer will have to experiment with supplemental foods. If he gives food one day and it is not eaten, he should stop that food and try another. Again, if he starts with small amounts only, he is not likely to run into trouble. While it is a good idea to test those foods most available to a farmer, here are some guidelines to feeding a number of pond fish.

Common Carp

Common carp feed well on the natural food produced in the pond. However, pond owners often give common carp supplementary food, so the fish will gain weight quickly. Some good supplementary foods for common carp are dried silkworm pupae, fish meal and clam meat. However, these carp will eat almost anything. Suplementary foods such as these are not necessary. The best way to increase common carp growth rates is to fertilize the pond well so that the pond produces a good supply of natural food for the carp to eat.

Tilapia

Not much is known about the feeding habits of some of the tilapia, for example, Tilapia nilotica. Tilapia mossambica and Tilapia zillii are used to control filamentous algae, which is a habitat for mosquito larvae, thus the tilapia is used to help with malaria control.

Tilapia are hardy and accept many foods. Most tilapia ponds can be managed in much the same way as carp ponds.

Chinese Carp

Chinese carp fry eat plankton, so it is important that they be placed in a well-fertilized pond with a good supply of natural food. Fry can be fed supplementary foods after a while. These foods include egg yolk which is strained through a cloth into the pond, soybean meal, rice bran, and peanut cake. Once the fingerlings get larger, they can be fed like common carp.

Remember, however, that the small pond owner is likely to have Chinese carp as part of a polyculture. If the polyculture has been planned wisely, the Chinese carp will not need to be fed extra food.

Indian Carp

Young fry of Indian carp, like all carps, feed on the plankton in the pond. Normally fish ponds in India are fertilized by draining the pond and drying, then adding a fertilizer made of some animal manure mixed with oil cake at the rate of 200 to 325 kg/ha. This produces a good bloom of plankton for the newly hatched fry. However, it has now been shown that the Indian carp prefer zooplankton, though sometimes they are given supplementary foods. After the fish reach fingerling size, no supplementary food is given.

Note that in any pond, the fish can be kept healthy, well-fed and growing well by making sure the pond is well-fertilized so that it produces its own food. As a general rule, it is better for most small farmers to work at keeping their ponds well fertilized or to find natural foods which can be added to the pond. Most small farmers do not have extra foods to share with fish, but they do have access to organic fertilizer materials, such as manure.

Fertilize the Pond. The section on "Preparing the Pond" discussed kinds of fertilizer, so the farmer should already be familiar with what fertilizers can be used in ponds. Again, the right fertilizer is a matter for experiment and experience.

The farmer has already used fertilizer before filling the pond. Now he must watch the water carefully each day. If the healthy green colour of a fertile pond is not there or if the water has become brown, fertilizer is needed. Fertilizers are applied depending upon what kind they are: REMEMBER: organic fertilizers do not provide their nutrients right away; inorganic fertilizers work very quickly.

A farmer who uses mainly organic fertilizers would probably be wise to keep some amount of inorganic fertilizer on hand for those times when he needs the fertilizer to work quickly.

Fertilizers are added to the pond in a number of ways:

* Leaves, grass, and animal manure may be left in piles around the inside edges of the pond. This is probably not a good way to fertilize in a hot, humid climate where the faster decay process would result in faster use of oxygen.

* Liquid manures and "soups" are dipped into the pond around the edges or in the deepest water.

* Powdered fertilizers (chicken manure, superphosphates) are broadcast (sprinkled) in a fine layer over the entire surface of the pond.

* Some fertilizers are left on platforms in the pond. The platforms are submerged near the surface of the water and confined behind a screen.

Watch for Predators. Check the pond area for signs of snake holes, rat burrows, eels, and strange fish which may have entered through holes in an inlet screen for example. Any of these can be very dangerous in a fish pond, particularly to a pond containing fry or small fingerlings. Make sure fences which protect ponds from farm animals who might eat grass off the walls or break down the walls of the pond have no breaks in them.

Not each of these things will require much time each day. But a good pond manager will at least check each of these items daily.

MONTHLY MANAGEMENT

Ponds which are managed well day by day will require little other treatment. However, the following things will probably require more careful attention every month or so:

* Check the pond walls. Cut grass which is too long or plant more, if necessary.

* Check the pond bottom. If there is too much buildup of silt and organic matter, shovel or scoop this material out.

* Check for and remove weeds or other growth which might be a problem at harvest time or when a net is used in the pond.

* Give the walls and inlet and outlet systems an especially careful check for leaks and for blockage. Make sure the water can flow smoothly in and out of the pond, so that if water needs to be put in or taken out quickly, there will be no problem.

* Check the fertility and turbidity of the water. Even a pond well-fertilized at the beginning may need more fertilizer after a month of operation.

* Check the fish carefully for signs of disease. If all has gone well during the month--the fish have gained weight and their gills are a healthy red colour--the chances are that all is well. But the fish should be checked especially carefully for signs of disease each month. (See "Problems of Fish Cultured in Ponds.") It does not take long for a disease to infect an entire pond full of fish.

* Add lime if needed. If the farmer has been adding fertilizer and feeding his fish regularly, but the fish still do not seem to be gaining weight well or moving in the water well, the water quality may need adjusting.

Good management is a key to a good fish harvest. It is important for the farmer to realize this and to work fish management into his daily schedule. But this is not always easy for him to do. In many parts of the world, farmers let their animals manage themselves, i.e., find their own food, etc. This will not usually work with a fish pond. Fish cannot be put into ponds, left alone, and expected to grow and provide food and income. Successful fish pond operation requires active attention by the farmer.

The management guidelines just described apply to all fish ponds, regardless of type of fish or stage of growth. There are, however, some differences between managing a fry or fingerling pond and managing brood stock. So these differences should be looked at more closely here.

Management of Fry and Fingerlings There are several ways to get fry. If the farmer is breeding fish, then he will have his own source of fry to bring to the rearing ponds from the smaller nursery (hatching) ponds. If the farmer has a small backyard pond, where he raises fish from fry or fingerlings to market size, he either gets his young fish from a market or another farmer or scoops them out of natural waters.

Wherever the young fish come from, it is important for a pond owner to know how many fry or fingerlings he is putting into his pond. If the owner knows how many fish are going into the pond he will know at harvest time how many fish died (the mortality rate) before they were ready for harvest. This information can help the farmer make decisions about his management of the pond. If, for example, more than half of the fish in a pond died between the time they were put in as fry and the time of harvesting for market, too many fish are dying; the farmer ought to find the reasons why before he begins again.

COUNTING FRY

Fry are very delicate and must be handled gently. Here is one way of counting them:

* Take a basin or tub of which you know the size (50-100 litres)

* Put all the fry into this basin.

* Scoop up fry into a 200-250ml measuring cup.

* Count the fry in the measuring cup by slowly and gently pouring the fish back into the basin.

* Estimate the total number of fry in the basin by setting up a ratio like this.

number of fry in measuring cup = volume of measuring cup

number of fry in basin (total) = volume of basin

For example, a measuring cup of 250 ml holds 100 fry. Therefore, it is estimated, using this formula, that a 50 l basin full of fry holds 20,000 fry.

Here is another way of counting fry which is somewhat easier because it does not depend upon cups and basins of any particular size.

* Put all the fry into an old container--an old metal garbage can, an oil drum, a washtub.

* Get an old milk can, or some other smaller container, and make sure one end is cut off.

* Fill the smaller container with strained water.

* Mark a line on the garbage can to show the level of water being put in.

* Fill the milk can and pour the water into the larger can.

* Continue to fill the smaller can and dump water from it into the larger can.

* Count how many small cans of water it took to fill the larger can as high as the line drawn on the can.

* Fill the smaller can with fry and count them carefully.

* Estimate the number of fry by multiplying the number of fry in the milk can by the number of cans it takes to fill the large container to the line marked on it.

Therefore, if there were 50 fry in one milk can, and it takes 25 cans to fill the larger container to the mark, there are 50 x 25 or 1,250 fry.

Fingerlings are easier to count than fry because they are older and larger. The same kind of measuring system could be set up. But the containers would have to be able to deal with the larger fish. A farmer who has raised his fingerlings from fry should count the fingerlings as he sells them or moves them from a nursery pond to a rearing pond. Then he will know how many survived. If a farmer started with 20,000 fry and had 15,000 fingerlings, 5,000 fry died. But this is a death rate of only 25%--which is not a terribly high figure. Again, the farmer must accept that some of his fish are going to die.

A pond owner who raises fish is more likely to be able to handle fry successfully. Fry are very delicate and must be protected carefully from predators and sudden temperature and oxygen changes. The fry hatch from their eggs in 12 to 72 hours depending upon the temperature and the type of fish. The fry then live off the yolk sac which is attached to them. This sac lasts several days. But then the farmer must be sure that the water provides enough food for the fry.

Many pond owners feed the fry with the yolk of a hard-boiled chicken egg that has been strained through a cloth with water. After a few days of this, the fry can begin to eat the phytoplankton and the zooplankton in the pond. Make sure that there is always enough food for the fry to eat before you transfer the fry to the rearing pond.

For a farmer who has only one new pond, it is probably a better idea for him to start with young fingerlings. This will give more chance of success than starting with fry.

This is not to say that a farmer who has only one pond cannot start his fish crop from eggs or fry. He can. One way this can be done is to keep the eggs in a washtub or large container rather than a pond. The eggs must have plenty of oxygen, so the water must be changed often. Any unfertilized eggs must be removed so that they do not cause infections in the fertilized eggs. Unfertilized eggs are white; fertilized eggs are yellowish red.

Keeping fry in a smaller container is a good idea because it allows the farmer to better control the surroundings. Fry often get bacterial and fungal infections and are a favourite target of birds. Again, the water must be kept rich in oxygen and food which can be eaten by fry.

The care of eggs and fry is very difficult and very important. A farmer who wishes to breed fish must certainly work to gain experience handling delicate eggs and fry. A farmer who wants only a food source in his backyard may wish to take the easier road and start with fingerlings.

The size of fingerlings depends upon climate, water temperature, food given, and the number of fish stocked in the pond. The following are some average sizes and weights common in the Philippines:

Average Average

Lengths Weights

Milkfish 6.57cm 2.9 grams

Tilapia 6.33cm 5.8 grams

5.64cm 5.6 grams

Silver Carp 7.39cm 7.1 grams

Common Carp 7.39cm 7.1 grams

Fingerlings may be fed supplementary food if it is necessary. Remember that fish usually receive supplementary food which is about 5% of their body weight per day. This was discussed in more detail in the section on preparing the pond, so there is no need to go into detail here.

It probably is a good idea, however, to note again that farmers should proceed slowly when giving supplementary foods. Add only small amounts of food and watch the fish carefully to see how they accept it. And the most important thing is to make sure the pond is producing enough of its own food.

If the guidelines for management, discussed earlier in this section, are followed, the fingerlings should grow well. When the fish reach a good size (the size preferred in the farmer's area -- some people like smaller, rather than larger fish), they can be harvested and sold.

A well-cared-for fence protects this farmer's pond from unwelcome visitors.

Breeding is the term used to describe the complete reproductive cycle of fish. Successful breeding depends on the health of the brood stock and the ability of the fish to spawn. Spawning describes the actual release of eggs and sperm by the adult fish, and the fertilization of the eggs by the sperm. This section gives information concerning the breeding of pond fish.

Management of Brood Stock

A brood fish is a fish that has reached its full growth and is able to reproduce. The age at which this happens depends upon the kind of fish, the climate, the quality and amount of food. The specific characteristics of brood fish are basically the same for every fish species. In general, good brood fish are:

* well-formed and unbruised

* free of parasites and disease

* lively and active

* a few years old, between 0.5kg and 3.0kg (depending upon species)

* sexually mature (so they can be separated by sex)

Other characteristics used in choosing good brood stock are relative size and the large, rounded abdomen in the female fish.

Choosing brood stock of common carp is more difficult. The characteristics of these fish are:

* moderately soft body

* broad and flat lower side of belly, so that the fish can stand on its belly

* relatively great body depth compared to length

* broad, but supple, caudal peduncle

* small head and pointed nose

* rather large and regularly inserted scales

* genital opening nearer to the caudal peduncle than in the average carp

In general, the larger the female carp, the more eggs it will produce. A carp of 45-50cm can produce up to 310,000 eggs; a carp of 60-65cm produces up to 1,507,000 eggs at one time. But older carp (5 years and up) will have eggs that are not as healthy as those of younger carp (2 years old), so size is not the only factor in choosing good breeders. Good breeders usually are younger fish weighing 1 to 2 kg.

Brood fish can be obtained from natural waters by seining (netting) or traps, from fish dealers or fishermen, from other pond owners, or from government fish farms. Select more males than females, so that when a female is ready to spawn, at least one male also will be ready.

The numbers of breeders needed depends upon the size of the brood pond. For example, a carp weighing 1 kg needs about [5m.sup.2] to live and spawn. Therefore, a brood pond of 0.5 ha (5,000 [m.sup.2]), will hold 1,000 brood fish of an average I kg weight. Most brood ponds are much smaller than this, however, so the farmer must calculate the number of fish to place inside. After some experience, the farmer will be able to judge the correct numbers for his pond quite easily.

After choosing the breeders, treat them for possible parasites or disease before placing them into the brood ponds. This treatment is done by placing the fish, one by one, into a bath of 10 ppm of potassium permanganate for 1 hour, them transferring them to a bath of 15 ppm of formalin for another 4 to 12 hours. These mixtures can be prepared in washtubs. After the fish are treated, they can be placed into the pond.

Of course, brood fish coming from a source which is known to be uncontaminated and free from disease would not require this treatment. (Further information on treating fish for disease is found in "Problems of Fish in Ponds.")

The brood stock must be well cared for. If they are in good health, the eggs will be healthier. It is probably more important to feed brood stock with supplementary foods than it is to give supplementary food to fish at any other stage of growth. Feed them rice bran, so bean cakes, or other processed foods at a rate of 5% of body weight per day. They should be managed carefully according to the general guidelines discussed earlier. Remember: brood stock should not be fed for at least one day before they are caught for breeding.

When caught by net, examine the brood stock carefully and handle them as little as possible. Use a cradle to handle and carry the fish from one pond to another. They should be carried to a spawning pond, stocked in the proper manner, and left to spawn. After spawning has occurred, the brood fish should be caught again and carefully carried back and released into their brood pond.

Always remember to treat brood stock well, and never select a fish for spawning which does not show the proper signs of readiness to spawn. (See the following information on spawning behavior.)

Spawning in fish ponds is done in two ways:

* Natural spawning -- the fish are placed in ponds and left to spawn by themselves

* Induced spawning (artificial propagation) -- methods used by man to make (induce) the fish release their eggs and sperm

Both of these spawning methods have advantages and disadvantages.

Natural Spawning. Fish who spawn naturally require only a well-prepared brood pond. Use a net to seine the pond and choose good breeders. Then introduce them into the spawning pond. Most fish will spawn the first night in the new pond; if they do not spawn, then leave them alone for a few more days. If they still do not spawn, remove them and start again with some other breeders.

Each fish used in pond culture has very definite and very different needs to spawn naturally in ponds. To encourage spawning, ponds can be prepared differently depending upon the fish. Therefore, the best way to prepare is to understand how that fish would spawn in nature. The following describes the natural spawning behavior -- in nature and in ponds -- of some of the more common pond fish.

THE COMMON CARP -- Spawning in Nature

In China, common carp spawn in the rainy season when the water level and temperature rise at the same time. This rise in temperature and water level is a signal to the carp to begin maturing sexually. When they are fully mature (ripe), they begin their mating behavior, which includes chasing each other in and out of the plants floating on the water surface. The farmer who sees his common carp doing this has a good indicator that his fish are ready to spawn.

When common carp are ready to spawn, the female carp begins to swim in and out of the plants. She then releases her eggs on the plant roots. The male follows her very closely. As she releases her eggs, he releases his sperm (milt); the sperm fertilizes the eggs. Carp eggs are slightly sticky (adhesive) and they stick onto the plant roots just under the water surface until they hatch. Depending on the temperature of the water, the eggs hatch in 2 to 6 days.

The new common carp fry feed off of their yolk sacs for another 2 to 6 days, until it is absorbed, and then begin to feed on the zooplankton in the pond water. The carp can spawn all year round in nature, as long as the water temperatures stay high, because a carp is capable of breeding once every two or three months.

THE COMMON CARP -- Spawning in Ponds

The best way to spawn common carp in fish ponds is to try and reproduce the natural conditions of high water levels and temperature. First the fish are taken from a cool pond and put into a pond with warmer water. Then the water level in the pond is increased. This provides the signal for the carp to mature sexually. When the fish mature, place egg collectors, called kakabans, in the pond, or just some water plants with roots that hang down.

After the introduction of the kakabans, the female fish begin to investigate the fibres. Soon the females will begin spawning behavior and the fish will spawn on the fibres of the kakaban. Because the eggs are sticky, they stick to the kakaban, and the entire kakaban can be lifted and transferred from the breeding pond to the nursery pond.

Important: Common carp are omnivorous; that is, they eat anything -- including their own fry. It is best to transfer the full kakabans to another pond for hatching.

A kakaban is a floating mat that uses a fibre like inkjuk, or beaten palm bark or leaves that have been shredded into long fibres. These fibres are bunched together and tied in the middle. The bundles are then nailed down between two long pieces of wood or bamboo and floated just under the water surface, with the ends hanging down into the water. This will look like the roots of water plants to the fish.

A kakaban is better to use for carp breeding than plants because it can be boiled and sterilized each time it is used. This will prevent any fungus or bacteria from attacking the newly-laid eggs.

TILAPIA -- Spawning in Nature

Tilapia spawn every month or so, as long as the water is warm. The male begins the reproductive behavior by digging holes in the pond bottom or side wall about 35cm across and 6cm deep.

The female will deposit her eggs, about 75 to 200 of them, in the nest, and then the male releases his milt. The female picks up the eggs and the milt in her mouth, so the fertilization of the eggs of actually takes place in the females' mouth. Tilapia often are called "mouth breeders."

The eggs remain in the female's mouth until they hatch -- 3 to 5 days. Then the fry stay in the female's mouth until the yolk sac is gone. During this time, the female does not eat.

As the fry grow, they continue to hide in the mother's mouth when they are threatened. The main reason for this mouth-breeding is for protection of the young fish, since the tilapia have relatively few eggs compared to some other pond fish. Tilapia is also a favourite food for a number of predators. Because the fry are so well taken care of by the mother (and even sometimes by the father fish), these young fish are easier to raise than some other species of fry.

TILAPIA -- Spawning in Ponds

Tilapia spawn well in ponds. It takes no special equipment or ponds. A tilapia needs only a pond with a loose bottom to spawn. The spawning ponds can be stocked with 25-30 females per [100m.sup.2] (1/100 ha) and about 40-45 males. If the temperature is warm enough, the males will begin digging holes in the pond bottom immediately, and the female will be attracted to the hole and release her eggs. From that point, spawning continues as in nature.

Tilapia will also spawn in ponds that do not have loose bottoms. In these ponds, place large-mouth pottery jars or wooden boxes on their sides on the pond bottom; the tilapia will use these containers as nests.

Young tilapia mature at about 3 months, when they are only 6 to 10cm long. They can then breed every 3 to 6 weeks, as long as the water is warm. In areas near the equator where the water is always warm, tilapia can breed almost continuously.

When a fish begins to breed, his energy goes into the development of his reproductive organs, not into bodily growth. The main problem with breeding tilapia in fish ponds, therefore, is the rapid reproduction of this fish. Reproduction can be controlled by sorting the tilapia by sex and placing them into separate ponds, or by producing a monosex culture by hybrid crossing. However, these methods can usually be done only by large commercial or government hatcheries where conditions are controlled.

The problem of fast breeding in tilapia ponds can also be controlled by using some natural predators of tilapia in the pond. The predators most often used are catfishes of the genus Clarias and, sometimes, eels like Anguilla japonica, and some other carnivorous fishes like Serranochromis robustus, in a polyculture with tilapia that are reproducing. These predators will eat the young fry, allowing the adult fish to continue their growth by having no competition for the available food.

CHINESE CARP -- Spawning in Nature

Chinese carp spawn in the large rivers of China when the spring rains cause the water levels of the river to rise. The eggs are found drifting down the rivers with the current, and they are collected by fry dealers as they drift. The main requirements for hatching Chinese carp eggs are a swift current and plenty of oxygen. Not much is known about their breeding habits in nature, but they are likely to show normal chasing behavior and then spawn, like common carp. Most Chinese carp are cultured by collecting their fry and eggs from the rivers in the spawning season.

CHINESE CARP -- Spawning in Ponds

The Chinese carp are all annual breeders. Good brood stock is chosen in the same way as breeders of common carp. Chinese carp breeders usually are kept in small ponds, separated by sex. When they are sexually mature, it is quite easy to tell them apart, since the males will usually leak milt when handled, and develop other body changes such as serrations (rough edges) on their fins.

Chinese carp brood stock must be well cared for, like all brood stock. They must be allowed to live undisturbed until time for spawning. However, the Chinese carp must be induced to spawn (see Induced Spawning).

INDIAN CARP -- Spawning in Nature

The Indian major carp will not spawn in standing water, so special ponds are built in India to provide a flow of water for these fish. These ponds are built like barrage ponds in upland areas so that the water flows through them. But these ponds are impossible to build in many locations, so the Indian carp often are bred by induced spawning.

In nature, the Indian carp spawn in rivers like the Chinese carp. The eggs are then collected and transferred to hatching ponds.

INDIAN CARP -- Spawning in Ponds

Good Indian carp breeders are sexually mature when milt comes from the male as it is pressed on the stomach. Ripe females have soft, rounded bulging abdomens and reddish genital openings. The breeders should be kept separated by sex in ponds prior to the breeding season, so that they will readily spawn when introduced into the breeding hapas. Usually one female is placed into a hapa with two males to insure that fertilization occurs. If a farmer can place the breeding hapa into a source of flowing water, he may be able to breed these fish naturally. If not, Indian carp must be bred with induced spawning methods.

A hapa is a rectangular box about 1m in depth and 1.6 - [6.5m.sup.2] in surface area. It can be made from mosquito netting with a mesh size of 3mm. Hapas can be made in many sizes. Some other dimensions of hapas used in Indian carp culture are:

91cm x 91cm x 183cm

91cm x 122cm x 244cm

91cm x 152cm x 305cm

91cm x 183cm x 366cm

The hapa is held in place inside the 'pond with stakes of bamboo or other wood. The breeders are put inside the hapa. Kakabans are placed below the water surface, and the top of the hapa is closed so that the breeders do not escape while mating. After spawning, the kakabans can be removed and taken to the nursery pond and the breeders released into the pond. Hapas can be used to spawn other fish as well.

THE GOURAMI -- Spawning in Nature and Ponds

The gourami build nests out of plant materials to lay their eggs. The eggs hatch in about 30 hours. The fry float belly-up for 5 days until feeding begins. The gourami can spawn all year round in warm water conditions.

This is a very good pond fish, and very easy to breed as long as you have a well-fed brood stock. The natural food of the gourami is soft leaves of plants like Colocasia and Carica. They can also be fed rice bran before breeding. Usually 10 females and 5 males are stocked in ponds as small as [100m.sup.2] and the eggs float until they hatch.

Breeding in ponds is done by merely placing the breeders together in a pond where there are some marginal plants available for nest building. Once the fry hatch and begin to feed, they can be stocked in nursery ponds.

OTHER GOURAMIS -- Spawning in Nature and Ponds The snakeskin gourami and the three spot gourami build nests made of air bubbles so that their eggs float. The kissing gourami scatters its eggs, which are free-floating.

To breed the snakeskin and three spot gourami, place the ripe fish into a well-oxygenated pond that has a good growth of aquatic vegetation, particularly Hydrilla verticillata. These fish will continue to spawn as long as the water temperature stays at 26 - 28 [degrees] C. Hatching takes place about 2 days after spawning, and the fry absorb the yolk sac within 3 to 7 days.

The kissing gourami spawn at 6-month intervals and spawn within 18 hours of stocking in the pond. Some of the eggs may be eaten by the parent fish, so there must always be abundant vegetation in the spawning pond to prevent this. The eggs hatch in 2 days and float on the surface for 3 to 4 days. The new fry eat the decaying plants and plankton in the pond.

CLARIAS CATFISH -- Spawning in Nature and Ponds

Clarias macrocephalus spawns during the rainy season in nests on the bottom of natural waterways, while Clarias batrachus spawns in horizontal holes in the banks. Hatching takes place after 20 hours at 25 - 32 [degrees] C. The fry are then collected by hand net from the nests. There are 2,000 to 15,000 fry in each nest.

Clarias catfish will spawn naturally in ponds, but induced spawning methods may be used if necessary.

THE TAWES -- Spawning in Nature and Ponds

The tawes spawn in the rainy season. Tawes ponds usually are about 200 to [500m.sup.2] and about 50cm deep. The ponds should be dried for 5 days before they are filled, and the spawners should be introduced when the pond is half full. Tawes need well-oxygenated water that has a strong current to spawn. Mating occurs at night; then the current should be turned off and the eggs spread out evenly on the pond bottom. The eggs hatch in two to three days. After 20 days, the fry can withstand the current, and it should be turned on again. Tawes females produce about 20,000 fry each.

HETEROTIS NILOTICUS -- Spawning in Nature and Ponds

This species is normally light-coloured, but during the breeding season it changes to dark brown. The spawning of Heterotis niloticus in nature begins at the end of the dry season when water is very warm. The fish splash in the shallow water among the weeds in the ponds to begin their breeding behavior. Then the male builds a nest of weeds in water that is 10 - 45cm deep. The nest is made in a depression that is 15cm deep and 60 - 100cm wide. The nest has a grass wall at its outer edge which keeps other fish out of the nest. To get in and out of the nest, Heterotis niloticus jumps over this wall.

The eggs of Heterotis are about 3mm in diameter, and are laid in the bottom of the nest and then fertilized. One of the parent fish is always in the nest to circulate water over the eggs (to give them oxygen). The eggs hatch in 4 - 5 days. The fry travel in a "school" and stay with their parent fish for several months after hatching. The fry are very delicate, and should not be handled for a while.

EELS -- Spawning in Nature and Ponds

The eels used in Taiwan (Anguilla japonica) spawn in the sea, and the fry (called elvers) swim upstream where they are collected by dealers. Eels, are stocked in rates of up to 25,000 fry/ha along with other fishes, and must be fed supplementary feeds like pellets of trash fish. It is not recommended that a beginner work with eels because they must be fed protein and are not very efficient converters of food.

Eels cannot be bred in ponds.

MILKFISH -- Spawning in Nature and Ponds

Milkfish spawn in saltwater during the rainy season. The fry are caught along the shore line at breeding season (which corresponds to the rainy season) and then transferred and acclimatized to freshwater ponds. This is done for the most part in the Philippines and in some other Southeast Asian countries like Indonesia and Taiwan.

Milkfish cannot be bred in ponds.

STRIPED MULLET -- Spawning in Nature and Ponds

The striped mullet is a saltwater fish, and spawns in the sea. The fry are collected as they swim upstream.

The mullet can be induced to spawn by hormone injection, but this is very difficult and certainly is not recommended for a small fish pond owner. Induced Spawning. Induced spawning means making the fish produce eggs an milt when they will not do so naturally. Induced spawning is done when the pond conditions cannot be made to encourage natural spawning, or when the fish are not ready to spawn when the farmer wants them to spawn.

Spawning can be done by three methods:

* hormone injection

* hormone injection with stripping

* stripping

Each of these methods has advantages and disadvantages.

Hormone Injection. Hormone injection is the most common method of induced spawning, and it requires certain kinds of equipment:

* hypodermic needle and syringe

* mortar and pestle

* saline solution or distilled water

* centrifuge

* test tubes

* dissecting kit

This technique uses the pituitary gland (the hypophysis) of the fish. This gland contains the substances(hormones) that trigger the reproductive organs of the fish to start developing. When these hormones are taken from a ripe fish and injected into a fish that is ripe, but has been unable to spawn, the injected fish will spawn in 6 - 12 hours.

The ripe fish must be killed to get the pituitary gland out. This must be done very carefully. The gland is very small: less than 1mm in diameter in the common carp, which has a relatively large pituitary. The pituitary gland is a round, yellowish-red organ located in the brain pan of the fish. Here is the method commonly used to take the gland from the fish:

* Use a mallet or dull knife.

* Hold the fish near the head with one hand.

* Hit the fish above the eyes at the point where the skull begins. This will kill the fish.

* Make sure to hit straight and up a little. A solid hit should dislodge the skull.

* Slit the skin around the front and sides of the skull, then lift up the top of the skull and fold it back as if it were a hinge.

The brain is attached to the top of the skull; by folding it back, the underside of the brain is exposed. The pituitary gland is located in the middle part of the underside of the brain.

If located in this way, the pituitary gland is relatively easy to find. However, this must be done carefully. If the skin is cut too much, or the fish is handled too much, the contents of the brain will move and the pituitary will be hard to locate. The brain contains a number of fat deposits which are yellowish and could easily be confused with a pituitary by someone who was not familiar with that gland.

Most farmers will not be interested in doing hormone injection spawning. But you should be familiar with and be able to do it. Steps for processing the pituitary gland and giving the injection are given below:

* Select the fish you want to spawn and weigh them.

* Select the fish that will be killed for their glands and weigh them. Always match the weights of the donor and recipient fish. If a donor is 1.5kg and the recipient is 3kg, use pituitaries from two 1.5kg donors.

* Kill the fish, as outlined above.

* Remove the pituitary from the fish matching weights (or use 2 to 3mg of dried pituitary gland for every kilogram of body weight.)

* Place the pituitary gland into the mortar.

* Grind the pituitary with pestle until it is a pulpy mass.

* Wash the pituitary into a test tube with 1 millilitre distilled water or saline solution.

* Place the test tubes into the centrifuge.

* Centrifuge the glands for 5 minutes.

* Remove the test tubes from the centrifuge.

* Draw up the liquid portion from the test tube into the hypodermic needle, leaving the pulp of the gland in the bottom of the test tube.

* Inject the fish above the lateral line behind the dorsal fin, just underneath the scale.

* Place breeders into the breeding pond.

All of the materials used in hypophysation can be found or made easily. A simple centrifuge can be constructed very easily from a hand drill (see next page for instructions). If a centrifuge cannot be found or made, the fish may be injected with a whole pituary gland. The gland may be dropped into the syringe, water added, and injected into the fish as outlined above. The force needed to push the gland out through the needle will crush the gland as if it were being ground with the mortar and pestle, and this will allow the hormones to be released.

After the injection, the female fish will begin to develop her eggs until they are ready for fertilization by the male. In some fish, it is necessary to inject the female twice with varying amounts of pituitary extract (see Chinese carp) and the male, once. After the injections, the fish are treated in the same way as in natural spawning.

MAKING A CENTRIFUGE

Tools and Materials:

* 1 hand drill

* 1 20cm piece small wood (or bamboo) dowel rod

* 2 metal cigar tubes (or plastic, or rubber hose with clamps)

* 2 pieces medium wire (long enough to wind around the tubes 6 or 7 times)

* 1 piece heavy wire about 9cm long (old coat hanger will work) cotton balls or pieces of soft material

* 2 test tubes or small clean glass bottles

* string, tape, and nylon fishing line

Construction Steps:

* Drill hole through one end of dowel rod about 1cm from the end.

* Remove drill bit from drill.

* Insert dowel rod into drill bit hole, leaving end with newly drilled hole at opposite end on top.

* Insert piece of heavy wire through the hole in dowel rod.

* Bend the ends of the wire into loops.

* Secure the wire on either side of the dowel rod with tape to keep the wire from slipping through the dowel rod hole.

* Wind medium wire around each cigar tube leaving about 2.5cm of wire free at the top of each tube.

* Attach tubes to heavy wire by bending medium wire (left over from step just completed).

* Place a small cotton ball in the bottom of each tube to cushion the test tubes.

Stripping.

Stripping is the term given to the method of actually pushing eggs and sperm out of the fish and mixing them in a dish. This can be dangerous to the fish, mostly because the fish can be hurt by pressing on the belly. Stripping is especially dangerous to a fish which is not ready to spawn. If the fish is ready to spawn, a gentle stroking motion down the side of the fish towards the genital opening will be enough to release the eggs or sperm.

First the eggs are stripped into a dry dish. Then the milt is stripped into the same dish. Mix the eggs and milt gently with a feather. Add water to the dish so that fertilization can occur. After a few hours and a few changes of water in the dish (to provide eggs with oxyqen), transfer the fertilized eggs to the kakabans and allow them to hatch as normal.

There are other variations of stripping that are worse than the one outlined above. One method involves killing the female or male, or both, and removing their reproductive organs and then mixing the eggs and sperm by hand. Not only is it necessary to kill both breeders, but if the eggs and sperm are not ripe (mature) and ready for fertilization, no fry will hatch.

Stripping with Injection.

Often stripping is done after the fish have been injected with hormone extract. The fish are injected, and the eggs are allowed to develop. Then the fish are stripped into a dry dish, etc. Stripping with injections works fairly well. But of the three methods of induced spawning described here, the best is just to inject the fish and let them spawn by themselves in the pond. The following paragraphs give directions for induced spawning of some important pond fish.

INDUCED SPAWNING OF CHINESE CARP

The Chinese carp must be induced to spawn by hormone injection. The normal dosages for bighead, black, mud, and silver carp are 2 to 3mg of dried pituitary or 3 fresh pituitary glands for every kilogram of female fish. That is, if the female silver carp weighs 2.5kg, 5mg of dry pituitary or 6 fresh pituitary glands are needed to ripen her eggs. Or HCG (human chorionic gonadotropin) can be used at dosages of 700 to 1000 IU (international units) per kilogram. But HCG is expensive and certainly not available to everyone. Grass carp need higher dosages (3 to 4mg dried pituitary per kilogram of body weight). Inject only a fraction (1/10 to 1/4) of the total for the first dose; then, follow it with the rest of the dose, 6 - 24 hours later.

After injection, put the breeders into the breeding pond. The temperature should be about 23 - 29 [degrees] C to encourage spawning, and the oxygen content should be at least 4ppm. It is best to put in two males for every female. Let the fish spawn on their own; they will spawn within a day. Remove the breeders after spawning.

Hatching Chinese carp is complicated. Chinese carp eggs need a constant supply of clean, well-oxygenated water flowing from the bottom up through the eggs to stimulate hatching. Some types of hatching bags have been developed for this purpose. One kind of bag hangs from a rack down into the nursery pond or a trough, and water is bubbled up by pipes from the inflow pipe. These bags have an advantage in that once the fry are hatched, they can easily be transferred without touching them at all. This is good, because Chinese carp fry are very sensitive to handling stress.

After the carp spawn, the eggs are collected by net or by draining the breeding pond, and they are placed in the hatching bags (or shallow trays) as soon as they have hardened after ferlization (1 to 2 hours). The eggs hatch in 1 - 2 days depending on the temperature, and then absorb their yolk sacs in another 3 - 6 days.

As soon as the fry absorb their yolk sacs, they should be transferred in the hatching bags to nursery ponds. The nursery ponds should be 0.5 to 1.0m in depth and the oxygen level should be at least 4ppm for good fry growth.

The spawning of Chinese carp is a very complicated business and is usually done inside carp hatcheries so that all conditions can be controlled. In China, the carp hatcheries sell their fry to fish pond owners who then raise them to marketable size. For most farmers, common carp is a much easier fish to work with and is just as valuable for food as are Chinese carp.

INDUCED SPAWNING OF CLARIAS CATFISH

The Clarias macrocephalus fishes are injected with pituitary extract at a rate of 13 to 26mg/kg at 25 - 32 [degrees] C. Spawning occurs within 16 hours. Larvae (fry) absorb the yolk sac in 5 days, and are transferred and reared in ponds only 18cm deep. The best food for fry is zooplankton, but after 2 to 3 weeks, trash fish may be added. They can be fed rice bran as well, and later on a mixture of trash fish, rice bran, and broken ice. In Thailand this sort of production gives yields of 97,000 kg/ha per year. Clarias catfish are used in fish ponds throughout Southeast Asia now, and are enjoyed for their good taste.

INDUCED SPAWNING OF INDIAN CARP

If you cannot build a fish pond like a barrage pond or spawn the Indian carp naturally in ponds, they can also be induced to spawn by hormone injection but this is very difficult to do. Induced spawning is dependent on the dosage and the stage of maturity of the breeders. Breeders should be about 2 to 4 years old, and weigh 1.5 to 5.0 kg. Females are injected twice, once with 2 to 3 mg of pituitary gland per kg body weight, and then, after 6 hours, with 5 to 8 mg/kg. Males are injected once, at the time females get their second dose, with a dose that is equal to the first dose given to the females. After the second injection, the fish are placed together in breeding "hapas" and spawning takes place within 3 to 6 hours. The breeders are put inside the hapa, kakabans are placed below the water surface, and the top of the hapa is closed so that the breeders do not escape while mating. After spawning the kakabans can be removed and the breeders released into the pond. The eggs should be transferred to deep hatching hapas where they will hatch in 15 to 18 hours at 27 [degrees] C. However, this induced breeding does not work as well as Chinese carp breeding, so most Indian carp fry are still caught and collected in natural waters.

INDUCED SPAWNING OF COMMON CARP

Sometimes common carp will not spawn in ponds, and they are injected. The amounts needed for common carp are determined by the fishes' weight. Usually the common carp is injected only once with pituitary extract from a fish that has the same weight as the injected fish. The male is not injected. After the injection, the fish are placed into the breeding pond. Usually a good female breeder will weigh 1 to 2 kg. This one large female is placed with 1 or 2 males, so that the total weight of the males is approximately the weight of the female. If you have a female of 2 kg, you can use two males of 1kg each. The more males, the greater the chance that fertilization will occur. If you have a large breeding pond, you can place about 5 or 6 large female fish and 10-15 males to insure that all the eggs are fertilized.

Carp will only respond to pituitary injections from other carp. However, many other fish will respond to the pituitary gland of common carp, so often carp are kept just to serve as donors of this gland in other induced spawning attempts. Also, carp glands are relatively large and easy to find, compared to the glands of other fishes, and can be stored for later use by drying, freezing, or powdering. Carp glands can be preserved by placing them in 100% dry acetone, then cooling them by placing that jar they are placed in, into an ice bath. Every 12 hours, the acetone should be changed, for a total of four times. Then the pituitaries are air-dried, and stored in an air-tight container. This is called the alcohol drying method; glands preserved in this way can still be used after 10 years!