The main differences between ponds and conservation dams are listed below:
| Ponds | Conservation dams |
| The main purpose is to grow fish. | The main purpose is to store water. |
| The water supply is controlled. | The water supply is not always controlled. |
| Only special kinds of fish are stocked. | Often there are many kinds of fish present naturally. |
| The fish are fed and the water manured or fertilized. | The fish are not necessarily fed, or the water manured or fertilized. |
| The fish are protected against predators. | The fish are not protected against predators. |
| The production of fish is large per unit area. | The production of fish is small per unit area. |
Dams and weirs for water conservation are common in parts of central east Africa where the rainfall is low and there is little water in rivers and streams during the dry season.
The dam or weir is actually the wall built across a stream or river to hold back the water to form a reservoir or small lake. However, in central east Africa, the whole place, i.e., the wall and the water it holds back, is called a dam or weir. In North America small conservation dams are usually called farm ponds, while larger ones are called lakes or reservoirs.
Dams and weirs fill up in the rainy season with water which may then flow over or around the wall. In the dry season the level of the water may drop and sometimes there is no water left at the end of the season.
Figure 42. A dam.
Figure 43. A weir.
The water stored in dams and weirs is used for many purposes, such as for cattle to drink, domestic supplies, irrigation of crops, or for driving turbines for electric power. In addition to all these functions dams and weirs can also be used to grow fish.
A dam is slightly different from a weir. In a weir the water overflows the whole wall, but in a dam the water overflows through a special place called a spillway (Figures 42 and 43).
In order to grow fish properly in dams there are three important procedures to be followed: (1) stumping and clearing the dam; (2) stocking the dam; (3) cropping the dam.
DAM STUMPING AND CLEARING
Stumping a dam means removing the trees, bushes and roots in the flooded area to below ground level. Stumps must be removed and roots must not be left sticking out of the ground.
Small dams, of less than 10 acres in area, should be stumped completely. In large dams this may cost too much, so only certain parts are stumped.
The best places in which to stump a large dam are where the water is shallow and where there are bays. If it is possible all places where the water is less than 15 feet deep should be stumped. Places where there are large rocks need not be stumped. Loose boulders can be removed and gulleys, holes, excavations, bumps and small anthills should be leveled as much as possible.
Stumping is done so that seine nets can be used to catch fish (Figure 44).
How to stump a dam
If a dam is stumped when it is built, the tractors used to make the wall can also be used to pull out stumps and level the ground. Laborers with mattocks, pickax and axes can dig out small stumps and roots. Stumping a new dam is done in the same way as stumping land for crops.
Figure 44. Where to stump a big dam.
Although most dams built in recent years were stumped when they were built, there are many in central east Africa which were not. Of these old dams many can easily be stumped when the water level is at its lowest at the end of the dry season.
In dams where there is always water, trees and stumps in shallow parts can often be pulled out with a winch (Figures 45 and 46).
Stumping a dam is very important because unstumped dams cannot be cropped properly.
Dam stocking
Kinds of fish in dams
Most dams in central east Africa have some kind of fish in them naturally. These fish were in the rivers and streams before the dam was made. The number and variety of fish occurring naturally in a dam depend on where the dam is located and the size of the river or stream which is flooded.
It is not within the scope of this manual to list the species of fish likely to be found in the various districts of central east Africa. It is, however, important to appreciate that in most small farm dams the only species of fish at all common, and that can grow to a fairly large size, are species of Clarias, the so-called barbel. Very few dams have the important species of Cichlids or so-called bream, such as Tilapia, Haplochromis and Serranochromis. These species have to be stocked.
Why stock a dam?
The reasons why a dam should be stocked are:
Most dams do not have Cichlid species occurring naturally in them.
If Cichlids are put into a dam, the amount of fish which can be produced is greater than if the dam is not stocked.
A certain kind of Cichlid, Tilapia melanopleura, will eat under-water plants, so that there will be fewer mosquitoes and places for snails to live.
There are special fish, such as Haplochromis species, which eat snails, so there will be less bilharzia and liver fluke.
Figure 45. Stumping a dam. Above: A dam with stumps in it. Nets cannot be used. Below: The dam with the stumps taken out. Nets can now be used.
Figure 46. How to use a winch to pull out tree stumps from a dam. (a) Equipment.
 | (b) Operation. The winch is tied to a big tree on the side of the dam, at (A). A sling is put around a tree stump (B). The cable from the winch is hooked on to the sling. |
Figure 46 (CONTINUED). How to use a winch to pull out tree stumps from a dam. (c) When the winch is worked, the tree stump is pulled out.
Figure 46 (CONCLUDED). How to use a winch to pull out tree stumps from a dam. (d) If a tree stump is hard to pull out, then a pulley block can be used. Tree stumps that are not in the water can be pulled out with a winch but at the same time the roots can be cut with axes and so make pulling easier.
Kinds of fish for stocking dams
In Zambia the most important kinds of fish to stock in dams are:
Tilapia melanopleura
Tilapia macrochir
Tilapia andersonii
Haplochromis spp.
In the Eastern Province of Zambia, Tilapia mossambica is used instead of T. andersonii for stocking dams.
In Rhodesia the fish most commonly used for dam stocking are Tilapia mossambica, Tilapia melanopleura and some exotic species such as T. macrochir and bass or even trout. Exotic species used for dam stocking will be mentioned in a later section.
Where to get fish for dam stocking
Fish for stocking dams are best obtained from government fish farms or fish breeding stations. It is possible sometimes to get fish for stocking dams from other dams, streams or rivers in the same area. This should be done under expert supervision, because the wrong kinds of fish are often taken if dam owners do it themselves. Ideally there should be a small fish breeding station for each area of conservation development.
Amount of fish for stocking dams
In Zambia the following amounts of Tilapia are recommended for dam stocking:
| Dams of 10 acres and under | not less than 20 lb |
| Dams of 10 to 20 acres | not less than 40 lb |
| Dams of over 20 acres | not less than 60 lb |
These amounts are for fingerlings of T. melanopleura, T. macrochir and T. andersonii in roughly equal proportions.
When to stock a dam
A dam can be stocked as soon as there is water in it. If the fish have to be sent a long way to a dam and the roads are bad, it is best to wait until the cool weather before sending them. In Rhodesia stocking of dams is not as a rule done in periods of severe cold weather, because of the danger of mortality. In Zambia such severe cold weather does not occur.
Dam cropping
Why crop a dam?
If a dam is properly stocked the fish will grow and breed and there will soon be too many. If there are too many, there will not be enough food to go round and the fish will not grow properly. So fish must be taken out of the dam; that is, the dam must be cropped.
When to start cropping a dam
In Zambia, if a dam has been properly stocked, cropping can start after the rainy season following stocking.
In Rhodesia, cropping is also started after the breeding season following stocking, but cropping is selective depending on the fish stocked.
Seine netting in dams
As with fish ponds, the best method of fishing dams is with a seine net, though the nets are larger than those used in ponds.
Of the many different kinds of fish caught in seine nets in dams more Cichlids are caught than other species.
The amount of fish caught each time a seine net is pulled will depend on the length of the net, where the net is set, how well it is pulled, the time of the year and even the time of day.
In large dams an average catch would be 20 to 50 lb per haul, but in small dams at low water, the catch might be as much as 100 lb per haul.
The two sizes of seine nets recommended for use in dams are of 1½-in. stretched mesh in the center and 2-in. mesh in the wings, 200 ft long or 100 ft long when mounted; the 200-ft net has a bag in the center and the 100 ft a bunt.
There is not sufficient space in this manual to describe in detail how a seine net is used in dams, but it is easily demonstrated (Figure 47).
It is very important to appreciate that seine nets can only be used in dams that have been stumped and where there is not too much underwater weed.
Gill netting in dams
Gill nets can be used in dams. Unlike seine nets, they are not pulled, but are either left in the water overnight or are set and the fish are driven into the net. With gill nets fish get tangled up in the net and drown. Gill nets are made of thin twine, usually nylon.
The kinds of fish caught in gill nets will depend on the kind of fish present and the size and mesh of the net.
Tilapia sparrmanii are readily caught in 2-in. and 3-in. stretched mesh gill nets, as are usually Gnathonemus macrolepidotus, the smaller Labeo spp. and Schilbe mystus. All species of Clarias, Tilapia and Serranochromis are also caught in gill nets, but not always in such large numbers as other species. The net mesh sizes of most economic value for use in most dams are from 2-in. to 3½-in. stretched mesh.
The amount of fish caught in gill nets varies very considerably. Sometimes as much as 40 or 50 lb of fish are caught in a 50-yd net in a night and sometimes nothing at all. More fish are usually caught if the net is set alongside grass and reeds and the fish are driven out from among the vegetation into the net.
Ground baiting has also been used with some success with gill nets, the nets being set around the area where the bait has been put.
As with seine nets, the method of use of gill nets is easily demonstrated (Figure 48).
Lines, traps and baskets
Long lines, traps and baskets are useful methods of fishing dams. Long lines are quite good for catching Clarias species. Traps and baskets are very useful for catching the small kinds of fish which are not caught in nets, such as small species of Barbus and Haplochromis.
Figure 47. How to use a seine net in a dam. Top: A seine net. For fishing in dams a seine net of 100 to 200ft in length is best. Seine nets may or may not have a bag. The net is put into a boat the same way as a gill net (see Figure 48). Center: Setting a seine net. The net is rowed out from A for about 20 or 30 yd. One end of the pulling rope is held by a man at A. When the end of the pulling rope is reached the man in the boat starts to put the net in the water (B). When the other end of the rope is reached (C) the boat continues to D, letting out the second pulling rope. As the net is pulled the men at A and D move toward each other. The net must NOT be pulled too quickly.
Below: Pulling the bottom rope. When the ends of the rope reach the shore, one man at each end pulls the bottom rope of the net and the others hold the top rope to keep the net out of the way of the man pulling. The man pulling must watch the middle of the net to make sure it is not closer to one side or the other. The net must not be pulled straight but rather U-shaped.
Figure 47 (CONCLUDED). How to use a seine net in a dam. Above: Holding up the net. As the net gets close to the side fish will start jumping out. Then the net can be held up. Below: Washing the fish, emptying the net and weighing the fish. When the net is at the side the bottom rope is lifted up. The fish are washed in the net and taken out and weighed.
Figure 48. How to set gill nets in dams. Above: A gill net. The length of the net is on an average 150 ft.
Loading the net into the boat. A net is put into the boat carefully, folding one piece on top of the other. It must not be rolled up or just thrown into the bottom of the boat.
Dams may also be fished with rod and line, because many of the small kinds of fish occurring naturally are caught by this method. Lines and traps are illustrated in Figures 49, 50 and 51.
It is important to remember that traps and baskets must never be put in weirs across the spillways of dams.
Figure 48 (CONCLUDED). How to set gill nets in dams. Above: In dams floating nets are usually used. They are put in shallow water up to 10 ft deep, so that the floats on the top of the net are on the surface of the water. In very large dams it is often a good idea to show where the net is by using a marker. The marker can be a thin stick put through a cork. A piece of cloth is tied to the stick as a flag. Below: Net on the bottom of the dam. In dams that are very deep, sink nets are sometimes used which are put on the bottom. To make the net sink to the bottom, more weight must be put on the bottom rope.
Figure 49. Lines set in the shallow water around the side of the dam.
Figure 50. Long lines. Above: Long lines set near the bottom. Below: Long lines set near the surface of the water.
Figure 51. Fish traps used in dams. A. Conical basket made of reeds. Set in small weirs or in shallow water among grass. B. Trap made of reeds. Set in shallow water. Often baited with maize meal. C. Drag basket made of reeds. Pulled through shallow waters. Sometimes set in lines and fish driven into the baskets. D. Perch trap. A wire frame covered with 1-in. chicken wire. Bait may be put inside.
When to fish in dams
In dams, lines, traps and baskets can be used all the year round, but it will be found that catches are larger at certain times of the year. For example, in the hot weather usually more fish are caught on rod and line than in the cold weather.
Gill nets can be used all the year round, but again more fish are likely to be caught in the hot weather than in the cold weather.
Seine nets are best used in dams at the end of the dry season when water levels are at their lowest and when there are no marginal reeds and grasses to hamper netting. Small dams are most economically netted for a few days only and the crop of fish for the year removed. Large dams, say 20 acres or more in area, can be netted for longer periods, perhaps every week for five or six months.
Crops of fish
The production or amount of fish that a dam can produce is not always the same as the amount that is cropped in practice. For example, a dam may be able to produce 1,000 lb of fish in a year, but in practice the actual crop taken may be only 300 or 400 lb, possibly because the dam cannot be netted properly.
The production — hence the crop of fish that a dam can produce — depends on a number of factors, such as stocking, quality of water, water temperature and the size of the dam, which have already been described.
In Zambia records have been kept over a number of years of fish crops taken from dams; these are listed in Table 1.
Table 1. - Fish crops from dams
| Size of dam (acres) | Average crops actually obtained (lb/acre/annum) | Crops obtainable with good management (lb/acre/annum) |
1 to 4 | 175 | 800 to 900 |
5 to 9 | 100 | 400 to 500 |
10 to 19 | 100 | 200 to 250 |
20 to 49 | 60 | 100 to 150 |
50 to 100 | 30 | 50 to 100 |
over 5 000 | 6 | 5 to 10 |
Size of fish
As a general rule the smaller the dam, the smaller the average size which Tilapia and other Cichlids reach. For example, in a dam of 5 to 10 acres in area, although there will be some fish that have grown to about half a pound, in a dam of 40 acres the size can be as much as 1½ to 2 lb.
Even if Tilapia are left for several years in a small dam, most of them will never grow larger than about ½ lb and the dam will be full of small-sized fish.
Experiments are being made in order to breed a fish that will grow large in small dams. It takes a long time, however, to obtain results from this work which can be applied in the field.
Improving fish production
The quality of the water in dams can be improved by manures, fertilizers and so on, thus increasing the food available for fish to eat. Phosphate is a good artificial fertilizer and can be put into a dam after the end of the rains when overflow has ceased. There is still much to be learned about the quantity of fertilizer to add to dams in different areas. A dose of 50 lb per acre of double-super-phosphate has given quite good results in areas where the water in general has a good alkalinity. In areas where water has poor alkalinity, lime should be added, at least at the rate of 100 lb per acre and at least a week before adding phosphate.
Many dams which are used as places for watering cattle are manured automatically; dung left around the edges at low water level is immersed when the dam fills up during the rains.
In small dams, fish can be fed directly with wastes such as maize hullings, beer wastes, waste vegetables and so on. Even if wastes are not eaten directly by fish, they will rot in the water and act as manures.
Loss of fish over dam spillways
Small fish and young fish are often found in very shallow water such as that in the entrance of a dam spillway. After a heavy rain these small fish may be washed over the spillway. The number of fish washed over in this way may seem many but in fact they are few compared with the total number of fish in the dam. Many fish try to swim up the spillway again and manage to do so if it is not too steep.
The erection of screens and traps in dam spillways to stop fish being washed out must not be permitted. It is dangerous as these screens can easily become clogged with rubbish and the water may then go over the dam wall and break it.
All dams have plants of some sort growing in them and around their edges. The amount of plants growing in and around a dam depends on the depth of the water and also on whether the dam has been stocked with T. melanopleura. If this fish is stocked the dam will have fewer plants. Some dams without T. melanopleura become completely choked with underwater weeds, so that even a boat cannot be rowed and nets cannot be used.
A dam with many water plants may also have more mosquito larvae, which are vectors of malaria, and snails that are vectors of bilharzia and liver fluke.
Marginal vegetation of dams is also eaten by T. melanopleura when flooding occurs and if the plants are not too old and tough.
Vegetation must never be planted deliberately in a dam, because the wrong kinds can choke up the dam completely. One very bad exotic plant that does occur in Rhodesia, but not yet in Zambia, is the water hyacinth (Eichhornia crassipes). Kariba weed (Salvinia auriculata), which has been a source of trouble in Lake Kariba and the Chobe River, is another plant that should not be introduced deliberately into dams (Figures 52 and 53).
Control of bilharzia and malaria in dams (See Appendix 2)
Bilharzia is a disease of humans and is caused by a minute animal which gets into the blood. This animal has a complex life history and at one stage lives within the body of certain kinds of water snails. Bilharzia is much more common in Rhodesia than in Zambia.
One way of controlling bilharzia is to kill the organism in the human with medicine. Another is to reduce the number of snails living in the water. Clearing water plants, mechanically or with fish, helps to reduce the number of snails, but this is not the complete answer. Though chemicals can be used to kill the snails, they may, however, also kill fish and the organisms on which fish feed. There are several kinds of fish which eat snails, such as species of Haplochromis. In small dams stocked with Haplochromis the number of snails is very greatly reduced (Figure 54).
Figure 52. Water hyacinth. Eichhornia crassipes. Water hyacinth floats in the water, but will also grow in wet mud.
Figure 53. Kariba weed. Salvinia auriculata. Kariba weed floats on the surface of the water.
 | Figure 54. Snails that live in water. Physopsis sp. and Biomphalaria sp. can transmit bilharzia. Lymnaea sp. can transmit liver fluke. Melanoides sp., Pila sp. and Cleopatra sp. do not transmit bilharzia or liver fluke. |
Figure 55. Top: Carp, Cyprinus carpio. Center: Black bass, Micropterus salmoides. Bottom: Yellow fish, Barbus marequensis.
Dams are often cited as a source of mosquitoes but these mosquitoes usually come from places around the dam and below the wall, where cattle have left footprints that fill up with water. Empty tins, or holes dug in the ground which have water in them, are places where mosquitoes will usually breed rather than in the dam itself, particularly if a dam is stocked with fish and properly managed.
Exotic fish species are fish that have been introduced into a country and are not indigenous. Some countries of Africa have very limited varieties of good sized, good eating fish occurring naturally, so fish of different species have been introduced from other parts of the world.
In the Republic of South Africa and in Rhodesia, bass, trout and carp have been introduced for dam and stream stocking. In Zambia there are very many different kinds of fish living naturally in the rivers, streams and lakes, and it has not been necessary to introduce exotic species for stocking dams or other waters. There is no point in introducing a new kind of fish to waters where fish that are just as good already occur naturally (Figure 55).
Some small dams dry up completely during the dry season, but even these can be used to grow fish. As soon as a dam has water in it, it should be stocked with Tilapia. When there is only a little water left, the dam is netted and all the fish taken out.
Dams stocked with 20 lb per acre of Tilapia can produce as much as 100 to 150 lb of fish per acre in about six months.
If there are a number of dams in an area, then a small, centrally located fish pond can be used for providing fish for stocking.
The brick tanks and reservoirs used for water storage on farms can also be used for breeding fish for stocking small, nonperennial dams.
In areas where dams are owned by local authorities, simple fish cropping schemes have been initiated. A successful scheme is one whereby the local authority employs fishermen who go from one dam to another netting fish with gill nets and a seine net, and who sell the fish locally. The money obtained is paid to the local authority.
Another less successful scheme is one where the local authority issues a netting license on the basis of one license per dam. The licensee nets on his own account and keeps all the profit. The disadvantage of this scheme is that licenses are often issued for dams that are too small and often unstocked; thus the licensee does not recover the cost of his license. In addition, licensees seldom have the capital for adequate fishing gear, such as a seine net.
By far the most important and damaging predators of fish in ponds are otters, Lutra maculicollis and Aeonyx capensis. These animals have been known to take up to 80 percent of the fish stocked in unprotected ponds.
The only sure way of protecting fish ponds against otters is to put a fence around the ponds.
There are a number of birds that will take fish from ponds, such as cormorants, kingfishers, fish eagles and herons. Cormorants become a nuisance and should be discouraged by every possible means. Ponds that are adjacent to a garden, or near the owner's house where there is some form of activity all day, are less likely to be affected by predatory birds than ponds that are isolated and seldom visited.
Predatory fish sometimes get into fish ponds down the furrow, particularly if the screen at the pond inlet is inefficient or broken. Since, however, these fish are usually small specimens, the damage they do is not very great.
There are some aquatic insects which will kill very small fish, but unless the damage they do is very great, no special precautions are taken against them.
The control of predators in dams is seldom a practical proposition, because of the situation of the dams and their larger size.
In properly managed ponds and dams that are regularly cropped, there should not be any serious or fatal diseases of fish.
Even under natural conditions, in rivers and lakes, most fish species have parasites. However, the fish have “learnt to live” with them and consequently do not suffer greatly, if at all, from the infection. The common parasites of fish in central east Africa do not infect or cause disease in humans.
In badly managed ponds and dams there have been instances of a disease known as black spot. This is caused by the larval stage of a flat worm (Strigeidae) that encysts on the body and fins of aged fish. In extreme cases of infection the cysts erupt as open wounds. Even so, no fish mortality has yet been recorded from this parasite.
Occasionally, infection of T. sparrmanii with a parasite in the snout of the fish has been noted. This parasite is also the larval stage of a flat worm, but again there is no record that it is fatal.
The Tilapia are extremely tough fish and are not known to succumb to endemic diseases. They also have remarkable powers of recovery from wounds. It is not uncommon to find healthy fish with fins missing, mouths distorted, or blind as a result of physical damage caused by bad handling, or even from predator attacks.
One of the most important things that must be watched for is the danger of a disease or parasite being introduced from outside, possibly in exotic fish imported for study or for ornamental ponds and aquariums. All imported fish should be kept in quarantine for several months before they are allowed anywhere near indigenous fish species.
Deaths of fish may and do occur from time to time in fish ponds and dams, not because of diseases of the fish themselves but because of changes in environment.
One known cause of fish mortalities in ponds and dams is poison, usually from vegetation growing near the water. All trees that have seeds in pods should be considered as potential fish poisons, i.e., Acacia, Bauhinia and so on. The seed pods on falling into the water release a substance that is capable of causing the death of fish, even if it is in very low concentrations. The effect of these poisons wears off in a few days. An indication of this type of poisoning is that the fish lose control of their swimming movements, “skittering” on or near the water surface and “gasping”. The water too tends to become clear.
Contamination of the water supply by insecticides and chemicals is another known cause of fish mortalities. Care should be taken to ensure that cattle dips and sprays are not sited so that they can overflow or drain into ponds or dams. In populated areas, detergents draining into streams can also cause fish mortality.
Another cause of fish mortality in ponds is lack of oxygen in the water, particularly at night. This oxygen lack can be caused by overfeeding, or, more often, by dense phytoplankton blooms. Over-feeding results in uneaten foodstuffs decomposing and using up available oxygen in the water. Dense phytoplankton uses up the available oxygen at night, although during the daytime, of course, there is ample oxygen from photosynthesis.
A lack of oxygen is usually indicated by fish lying near the surface of the water and “gasping.” The remedy is to run in fresh water.
Certain minute plant organisms, e.g., Microcystis toxica, if in large concentrations can cause deaths of fish. It has not, however, been recorded from ponds in central east Africa.
Although Tilapia are very tolerant of temperature changes, there have been recorded cases of death occurring as a result of low water temperatures in too shallow ponds particularly when cold water is run into ponds at night. In places where there is a danger of low night temperatures, water should only be run into ponds in the daytime.
As a general rule the lowest lethal temperature, over a period of time, for Tilapia species in central east Africa is about 11°C (52°F) although T. sparrmanii can withstand temperatures a few degrees lower.
It is most worthwhile to engage in fish culture in close association with irrigation, vegetable growing and intensive rearing of poultry and pigs. The costs of building a furrow to the pond are then shared between the pond and the irrigation. Maximum use is made of the by-products and nothing goes to waste. While the small unit of one or two ponds may have its place, the aim should be a number of ponds which can be run as an economic proposition in association with other activities.
Poor waters can be made more productive by the right use of lime, fertilizer and food and the better the management the higher the yields. The mark of a good fish culturist is not how much he spends on foods and fertilizers but the wise use of available resources to get the best possible yields from the ponds. Good economical management results in yields of 1,000 lb to 2,000 lb per acre and may in some cases be even higher.
Where foodstuffs are costly and have to be transported it may be more profitable to grow fish by using only fertilizers and green-stuffs as a food. Careful thought must be given to the price of feeds, the selling time of the fish and the total yield expected.
It is necessary in order to see where improvements can be made and for the efficient running of the ponds to keep accurate figures of crops taken, stockings (date and amount) and costs of the enterprise. A simple record sheet is shown which can serve as a basis for pond records. Changes can be made to suit the individual farm needs. (See page 140.)
Figure 56. Left: Cans and drums for fish transport.
| Large can | Small can | |
| Water | 20 gal | 11 gal |
| Weight with water | 200 lb | 110 lb |
| Fish | 8–10 lb | 4–5 lb |
The two cans of different sizes are made of galvanized iron sheet, 22 or 24 gauge. All
joints are riveted and soldered.
Right: A 44-gal drum.
The three most effective ways of transporting live fish in central Africa are:
In special fish cans or 44-gal drums (Figure 56).
In a special fish tanker, used for large quantities of fish, 300–500 lb.
In polythene bags, used for small quantities of special fish sent by air.
In all methods of transport of Tilapia (Figure 57) there are certain important rules to be observed to ensure success:
The containers must be clean.
The water must be clean.
The fish must be clean.
The water temperature must be as low as possible, but not lower than about 15°C (59°F). Ice can be used to lower the water temperature. It follows, therefore, that the best time of year to transport fish is when the weather is coldest.
The size of fish should be between 3 to 6 in. in length and the best length is 4 to 5 in.
Avoid handling the fish with the hands as much as possible.
If fish are being sent long distances the survival rate can be improved by putting the fish in concrete or brick tanks over-night, so that their guts empty and the fouling of the water during transportation is reduced.
When unloading Tilapia into ponds or dams there is seldom any need to make the temperature of the water in the container the same as the water of the pond or dam. Tilapia are able to withstand temperature differences of 5.6° to 8.4°C or of 10° to 15°F. For differences greater than these it is better to equalize the water temperature in the container with that in the pond or dam.
Figure 57. Method of catching and handling live Tilapia species. A. Make sure the can or drum does not leak. Fill the can or drum to the level with CLEAN water. B. Net the stock pond. Use a net of 1-in. or 1½-in. stretched mesh. C. Wash the fish in the net in the pond. Carry fish from the net in a hand net.
 |  |
 |  |
Figure 57 (concluded). Method of catching and handling live Tilapia sp. D. Weigh the fish in clean bath, without water. Weigh about 5 lb of fish at a time. Take out any kinds of fish that are not wanted. Write down the weight of the fish. E. Put the right amount of fish in the can or drum: large can, 8–10 lb; small can, 4–5 lb; 44-gal drum, 12–15 lb. F. Tie the lid on the can. Attach a label. Send the fish away. Do not leave the can standing in the sun. G. If cans containing fish have to be kept standing for any time, then the water must be aerated. This is done by dipping water out and pouring it back with a tin or cup. When the can is on a lorry or a car, the water is kept aerated by the bumping of the vehicle. On a long journey by road some water may be lost from the cans, so clean water should be put in now and again to keep the cans full.
Not all fish are necessarily as easy to transport as the Tilapia, although the Serranochromis are fairly resistant to handling and can be transported with Tilapia. Certain Haplochromis, however, are more difficult. These species should not be carried in the same container as Tilapia as they tend to die more easily, and by fouling the water cause the deaths of other species present.
In many parts of the world certain chemicals called tranquilizers are used to quiet fish when they are being transported. Tranquilizers have to be used carefully and are not always reliable. They are not necessary for local distribution of Cichlids in central east Africa, where the best form of tranquilizer is cool water.
The preservation of fish means keeping fish acceptable for consumption for some length of time by using the methods needed to prevent deterioration. (See Appendix I.)
Preservation of live fish
The simplest way to keep fish alive is to leave them in a rearing pond, or to place them in a special small storage pond, where care must be taken to ensure a sufficient inflow of fresh water. If only small quantities of fish have to be handled, it is suggested that they be placed in a small floating fish sump, kept in the pond near the inflow of water (Figure 58).
Figure 58. Left: A fish sump floating on the surface of a pond near the intake furrow. Right: A fish sump.
The live fish must be placed in a storage pond or a sump immediately it is caught, though this should be avoided in winter when the water is cold.
Preservation of fresh fish
The process of preservation with regard to fresh fish must start from the moment the fish is taken out of the water. Bacteria that cause deterioration are always present. They are mainly concentrated in the gills and guts where deterioration starts first and from where it quickly spreads through the lymphatic and blood systems throughout the whole body. The first thing to do, therefore, is to remove the gills and the whole inside of the fish. For gutting, the full length of the belly is split open with a sharp knife. Care must be taken during the cleaning process to cover the fish with wet weeds, wet bags or at least to avoid exposing them to the sun.
After being cleaned in this manner, the fish should be kept for about one minute in a cold bath of a solution of 0.2 percent saltpeter (sodium nitrate). This solution is prepared by means of dissolving 28 grams (1 oz) saltpeter in 12½ liters (3 gal) of water (Figure 59).
Naturally, if ice or refrigeration is available fish can be kept fresh for a longer period.
 | Figure 59. A container with prepared saltpeter solution. The container is half filled to avoid spilling when dipping the fish. |
If the fish is disposed of quickly, cleaning is not necessary. Dipping into the saltpeter solution and cooling on ice or by refrigeration, if available, is all that is needed.
Preservation of fish by drying
The preservation of fresh fish is only possible in cases where it reaches the consumer in a short time. The most popular way of preserving fish for a longer time is, in central east Africa, to dry it in the sun.
There are many ways of drying fish:
Drying in the sun when fresh;
Drying in the sun after a preliminary heating/smoking over a fire;
Drying fresh fish by the cold smoke curing method;
Drying in the sun after a preliminary salting.
To get dried fish of good quality it is essential that only fresh fish of an impeccable standard be used. No drying method will improve the quality of a fish which has already partially deteriorated.
The same procedure is employed in preparing fish for drying as that described in the chapter on the preservation of fresh fish with the exception that, when cleaning, the fish is split at the back along the dorsal fin, so that the head is also split into two halves (Figure 60). This is essential because the fish is thickest at the back, and by splitting it in this way drying will take place more evenly over the whole body.
| Figure 60. Fish split along the back. |  |
Drying fresh fish
Fresh fish prepared in the manner described above is spread out to dry in the sun on rocks, grass mats, or screens. No further preliminary preparations are necessary. To ensure even drying, the fish should be turned periodically. As the drying process may take many days, the fish should be gathered up and put into tight heaps each day before sunset. Next morning, after sunrise, they should be spread out again, and the procedure repeated until the fish is thoroughly dry but not brittle. This method of drying is applicable only to small-sized fish. In the case of larger sized fish deterioration may set in before the fish has had a chance to dry properly and other methods of drying have therefore to be applied.
Attention should be paid to the seasonal appearance of certain kinds of flies and beetles which may cause great damage to the fish when drying. They lay eggs in the flesh and heads of the drying fish and the product may be completely ruined by their larvae. Preliminary salting and smoke curing does prevent attacks by insects to some extent.
In air temperatures of over 38°C (100°F) it is advisable to dry the fish in the shade, or hung up on stretched wire or on sticks, as fish lying flat in the hot sun may be baked before they are dried.
Drying by preliminary heat/smoke curing
The prepared fresh fish is heat/smoke cured before being spread out to dry. For heat/smoke curing the fish is placed for 10 minutes on a grid under which a smoking, smoldering fire is kept burning (Figure 61).
 | Figure 61. Heat/smoke curing of fish on a grid. |
Drying by preliminary cold smoke curing
The prepared fresh fish is hung up, or placed on a screen, 6 feet above smoking and gently smoldering logs in a smoking hut. The fish can be kept there until completely dry, in which case further drying in the sun is not necessary. Or the fish can be kept in the smoking hut until it has attained a certain degree of dryness and then set out in the sun until the drying process is complete. Although cold smoke curing may last for days, it has the advantage that insect damage is kept at a minimum (Figure 62).
Drying by preliminary salt curing
This method of drying is somewhat more elaborate. A wooden box, or any container, the bottom of which is holed for drainage, is needed for salting. Crude salt is used for salting, at a ratio of 1 lb of salt to every 4 to 5 lb of fish. First, a layer of salt is spread over the bottom of the box or container. Then a layer of prepared fresh fish is tightly packed on top of it and covered by another layer of salt. Thus alternate layers of fish and salt are tightly packed into the container, finishing with a layer of salt. Care must be taken that the salt is spread evenly between the layers of fish. The container should be kept, wherever possible, in a cool place (Figure 63).
The salt will dissolve in the fluid of the fish and penetrate into the flesh, while the excess fluid will begin to run out through the holes in the bottom of the container. Next day the fish should be taken out of the container and repacked in such a way that the fish previously on the top will be placed on the bottom. No new salt is added.
Figure 62. Reed or grass hut for cold smoking measuring 6 × 6 × 9 ft. In order to have a view of the inside one wall is omitted from the figure.
Figure 63. Dry salting in a wooden box.
Care should be taken, however, to see that no salt stuck to the fish is brushed away and that all the undissolved salt which remains is put back carefully between the layers. It is useful to have two identical containers. In this case relayering is done by lifting the fish layer by layer from the first container and putting them straight into the second. Thereafter, changing top to bottom layers must take place every third day, until no more liquid seeps through the holes and almost all the salt has dissolved. The fish is then ready for drying in the sun.
In very hot weather when the air temperature rises to over approximately 32°C (90°F) the dry salting method may prove too slow, and the fish may deteriorate before the salting process is accomplished. In such conditions the method of wet salting is suggested.
For wet salting a container, such as a bucket or a drum, is half filled with water. Enough crude salt is added to the water so that when as much as possible is dissolved a thin layer of salt remains on the bottom. The fish is then placed in the salt solution and kept there for about 18 hours. Thereafter the fish is spread out for drying in the sun in the usual way.
If desired, the salted fish can be treated by smoke in a smoking hut, which gives it the taste and appearance of smoked fish.
Storing
Fish, if properly dried, can be stored for some length of time. It should be kept tightly packed to prevent it from turning rancid and to protect it from the moisture in the air. The fish must also be protected from insects which eat it and lay their eggs in it, the larvae causing the product to deteriorate.
Use of fish offal
A considerable amount of offal is usually left after the fish are gutted. Such offal should never be thrown away. It should be used for feeding domestic animals, such as pigs and poultry, and the oil should be extracted for human consumption.
The fresh guts, gills, heads and some undesirable kinds of fish can be chopped into small pieces and fed to animals, especially poultry, in a raw state. Some fish, and especially their offal, are, however, rich in fat and too much fat in animal feed is not desirable. It is preferable, therefore, to extract the oil from such offal.
The procedure for the extraction of oil is very simple. All that is needed is a container four times as big as the amount of offal. This is half filled with water which is brought to the boil (Figure 64).
| Figure 64. Boiling of offal for extracting fish oil. |  |
Finely chopped offal to the amount of half the volume of water is then added to the boiling water and kept boiling for 20 minutes. The container is then taken off the fire. When the offal has set and the oil risen to the surface, the oil is skimmed off.
Oil extracted in this manner has a very high nutritional value being rich in Vitamins A and D. It is generally used as cooking oil.
The oil-free residue, when it has cooled, can be fed to animals by mixing it with other animal feeds. Or it can first be poured into a tightly woven cloth bag, the liquid squeezed out and the liquid and the residue then fed separately to animals.
