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close this book SPORE No. 21 - January 1989
View the document Pisciculture : a growth industry?
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Fish from farm ponds

The most widespread technique is rearing in ponds. It is the simplest, the most economic, and probably the best suited to the environment. In Cote d'Ivoire, where this type of pisciculture is taking off in a big way, the ponds seem to make a totally natural addition to the hollows next to the ricefields or just below the little artificial reservoirs built in the last few years for agricultural or pastoral purposes.

These ponds fit in well with the landscape and are well adapted to the existing infra structures, and also to the local resources for fish feeding. Fish farmers collect agricultural waste matter or rubbish, and use it for fertilizing the ponds; as it decomposes the vegetable matter produces organisms which make a fish food of unrivalled cheapness and this method of rearing provides farmed fish at probably the lowest possible cost. But from the point of view of return on investment it is not very viable economically.

It is for this reason that research has been carried out into other more "rewarding" methods. If small-scale or industrial agriculture produces by-products - such as ricebran or cottonseed-cake - within easy reach of the fishponds, then these can be used as food. Fish grow faster and bigger on these processed by-products than on untreated vegetable waste as they have a higher nutritive value. They are cheap, and are well adapted to the nutritional needs of the fish and to the climatic conditions. which is not always true of imported food from Europe, which reacts badly to heat and humidity. In Cote d'Ivoire, for example, fish were fed on cottonseed-cake which was completely infested with weevils. The fish ate it as voraciously as usual and their weight gain was comparable to that of the preceding months when the cake was not contaminated.

Fishrearing in ponds fits in as well with stock-keeping as with crop-growing. Ponds with small huts built on piles over them housing ducks and chickens,(just as in China) are beginning to make their appearance in the African landscape. They produce up to four tonnes of fish/hectare per annum. But people are still very loath to eat fish fed on poultry droppings, though in some areas the taste of tilapia has overcome this reluctance.

More intensive production

If fishponds are the simplest and most appropriate means of rearing, they are nevertheless neither flexible, because of the existing infrastructure, nor economical in terms of water use. The new climatic situation created by the drought years has caused some countries to look to other methods of fish-farming which might be better suited to restricted water supply. In Niger, cages have been set up in the river, and in Cote d'Ivoire and Benin attempts havebeen made to exploit their lagoons by building enclosures.

Trials have been done to make this technique intensive (10 to 100 fish per cubic metre) while at the same time keeping it smallscale. Both cages and enclosures are lightweight constructions made using simple technology and locally-available materials where possible: wooden rafts, bamboo stakes, 30-litre plastic drums for getting the fish out, grilles made out of fishing nets or (imported) plastic. These constructions are easy to handle and can be moved by three or four men when necessary.

This is still a relatively new field and the different phases in the rearing of the fish, although now defined by research, demand certain technical skills on the part of the fish farmer. Not every problem has yet found an answer. Firstly, the financial return on fish produced in this way is small compared to that on fish caught in their natural environment, and the price of fish-food has a big influence on this. The food must be of assured quality, balanced, and carefully measured.

There is an increasing move towards feeding the fish with locally-available by-products, as with the fishpond method, and this would seem to be appropriate in every way. In Niger, for example, the fish in cages are fed mainly on rice-bran and peanut oilcake, and this suits them well. The last weight-month season brought in 500kg per 20 cube m cage. But despite all this, caged or enclosed fish do not thrive as those in the wild or in a large pool: disease is a greater risk because of the density of numbers, and it can bankrupt the fish farmer. In the enclosures in Benin, stock density has been voluntarily reduced (approximately 10 -15 fish per cu m) in order to lessen the likelihood of infectious disease.

In Niger problems peculiar to that country have been encountered. In the cold season (December-February), when water temperature is lower than 20°C (against 35°C in the hot season). the fish failed to grow or reproduce, and sometimes died. When feeding was adjusted more accurately to the water temperature the fish came through the season much better. At present about 50 Niger fishermen have changed back to aquaculture, using some 200 cages which provide them with their main means of income.

In Benin, where 30 or so enclosures have been implanted in Lake Nokoue, the problem is salinity: from 20g per litre in 1984 the salinity of the water has risen to a maximum of 30g per litre in 1988 and such an increase can be crucial to freshwater fish. Research is in progress to find new species of hybrids better suited to salt water but in the short-term, the fishermen are looking to the Porto-Novo lagoon where salinity is lower and where the species of tilapia used is in its element.

Trials are also going on in Cote d'Ivoire, in the Ebrie lagoon, to try and overcome the salinity problem. The first results of these seem to suggest that the problems in rearing tilapia in lagoons are not just caused by salt: it is a complex environment where other characteristics than salinity may disturb the tilapia. What are they? Can they ever be overcome? Research is in hand that may eventually allow the resources of these large expanses of lagoon on the African coast to be fully exploited.

Smallholder fish farming

A productive method of farming tilapia has been widely adopted in the Masasi district in south west Tanzania. The fish can be eaten by the smallholders, sold, or used in exchange for other commodities or services.

Each smallholder fish farmer gets advice and buys stock from a central fivepond demonstration site. This is the base for a Tanzanian fisheries office and a fisherman from Voluntary Service Overseas, who help with the planning, construction, stocking and management of each pond. The integration of the fish farm with current crops and livestock and water supply are the most important considerations.

For a pond to be easy to manage it needs sloping grassed banks that reduce erosion and a screened inlet and outlet to prevent wild tilapia from entering. Because nets are expensive, it is preferable to harvest by hand, so it is necessary to be able to drain the pond completely. Hired workers are paid in fish.

The fish are fed daily on waste products from the smallholding or'shamba': maize or rice bran, chopped pawpaw, cassava and banana leaves. The maize bran floats and, when the fish surface to feed, their size can be assessed. Tilapia breed so rapidly that overcrowding can occur. There are three ways of feeding fish in ponds: with agricultural waste, with duck droppings or pig manure. These waste products encourage the growth of phytoplankton, on which the fish feed as they decompose.

Cow manure is put in the water in a woven basket to promote algae and plankton blooms, on which the young fish feed. Fed in this way, it is possible to harvest the tilapia after three to four months. However, harvest is usually a little later than this as many of the fish ponds are run as a sideline for the farmers who have other livestock to attend to.

News that a pond is ready for harvest spreads quickly and villagers will collect at the pondside. Those fish farmers who have no other livestock will pay for manure with fish.

One aspect of tilapia farming which the project hopes to develop is the integration of duck and chicken production. They would be housed above the water, hat their manure would fall into the pond and feed the algae and plankton.

Using tilapia hybrids that produce all male offspring and sex reversal with testosterone to prevent breeding could produce large, uniform fish for the western market. But at present the more appropriate basic tilapia husbandry makes enough demands on the smallholders'time

The one hundred ponds constructed by villagers with the help of Maliasili and VSO/ODA staff produced well over a tonne of fish per year, and more ponds are planned.

Tilapia, the African carp

At present, tilapia remains the most common "farmed" fish in lagoons: despite the passage of time and despite competition from newly-domesticated species, it still comes top.

To the Africans who eat it stewed or in a sauce, tilapia, Saotherodon or Dreochromis niloticus, commends itself by its hardiness and its qualities as a survivor (90% plus survive in pools). Furthermore, it thrives: it can put on one or two grammes a day if well fed, and its conversion ratio is three kg food into one kg of flesh. Unlike predatory fish, which are cannibals, tilapia eat phytoplankton (microscopic vegetable organisms) and thus is at the beginning of the food chain. And it reproduces in captivity, without outside help - unlike so many other species.

Perhaps it even reproduces a little too well. If one is not careful the pool stocked with tilapia can quickly become overpopulated as the female lays eggs from a very young age and with extreme frequency. This results in large numbers of very small fish, which are virtually impossible to sell in some countries. This problem does not occur in the cage or enclosure rearing techniques where the tiny fish pass through the mesh of the nets and escape.

However, there are techniques which can avoid this problem and grow good-sized marketable tilapia - about 250g. One practical, yet simple, method consists of sexing the tilapia manually and separating out males and females (the males grow almost twice as quickly as the females).

Other methods are more sophisticated, but are also being t aken up. For instance, allmale hybrids can be produced by crossing certain types of tilapia; or the sex of the recently-hatched young fish can be changed by hormonal treatment which is produced chemically and mixed with the feed.

Manual sexing, which is the current technique in pisciculture in country areas, may be simple but it has its drawbacks, the main one being that it is not always totally reliable. A few females will always manage to slip in. Extra precautions have to be taken, therefore, and predators (fish which feed on smaller fish) introduced. One of the most commonly chosen is Hemichromis fasciatus, which is relatively hardy for a predator and which has the advantage of growing very slowly - for the bigger the predator, the bigger the fish it eats, and this can be counter-productive after a while as it decimates those fish intended for the table. Another commonly-used predator, Clarias gariepinus (still called the African catfish) is less useful as it eats not only baby tilapia, but also their food.

Looking to the future

Where will African pisciculture be by the year 2000? "It shouldn't be thought that pisciculture will be the answer to the shortage of animal protein in those countries which are currently forced to import" - this is the opinion of Jerome Lazard, head of the fish and fisheries division at CIRAD-CFTC. "The strength of pisciculture at the moment resides in its small scale and the way it adapts to the environment - but this also constitutes its weakness. By fitting in so well with the peculiarities of each method of agricultural production, it therefore lends itself to being taken over by the operators (peasants, fishermen...). But this can be a two-edged sword: time is needed to introduce a new activity into the heart of existing structures without causing disruption".

Fish-farming is not some factory rearing procedure which can be built up from nothing overnight. In Burkina Faso and the Congo attempts in this direction have met with serious difficulties. Would it be too soon to move from an integrated system to pools "with vacant possession"? Fish farmed on an industrial scale is not yet as competitive as seafish, even though this does have to travel, deep-frozen, 2000km inland. The density of stock means disease is more common. But despite this, it does not mean that this sort of pisciculture should be condemned out of hand. and there are some who would recommend it. Despite the problems it has encountered up till now, it may yet have a role to play.

Already, despite unfavourable opinion from scientists, private companies are paving the way towards fishfarming on an industrial scale. Return is as yet low on big investments, but there are entrepreneurs who think "it will work out in the end". Has it not always been the same? From the gatherers of long ago to the agriculture of today, from village production to agri-business, the story of food and farming has been one of trial and error.


Nash C., 1987. Future economic outlook for aquaculture and related assistance needs, FAO, ADCP/REP/87/25 Rome

CRDI/ IDESSA/PNVD-FAO-MINEFOR. Atelier sur la recherche artisanale du tilapia en Afrique: analyse du differents systemes d'elevage et de leur niveau de developpement. Bois et Forets des Tropiques, CTFT, Nogent/Marne n°216