SECTION III: SYSTEMS AND TECHNIQUES OF AQUACULTURE (contd.)

FERTILIZATION AND FEEDING PRACTICES IN WARM-WATER POND FISH CULTURE IN AFRICA

by

James W. Miller
FAO Fisheries Expert
Central African Republic

Abstract

The use of organic fertilizers, inorganic fertilizers and feeds in warm-water fish culture in Africa is reviewed and examined. Composition of various fertilizers and feeds is presented, as well as advantages and disadvantages where possible. The use of lime is discussed. The use of inorganic fertilizers appears limited in most countries due to high costs and limited availability. However, the possible profit index from fish culture with inorganic fertilizers or feeds appears about the same (5.73 and 6.06 respectively). Use of organic fertilizers, such as manures and compost, appears limited to rural, familial ponds. But associated husbandries such as raising pigs over fish ponds offer a direct system of organic fertilization which is increasing in popularity. The quantity and quality of feed stuffs for use in fish culture appear to be increasing in Africa. Still, the efficiency of most fish cultures - largely monocultures of tilapia-in Africa appears poor. Much more research is needed to develop better methods of tilapia culture involving fertilization or feeding. Polycultures need to be developed, thus, much research needs to be done on evaluation of local species for culture. Efforts in applying modern feed technology, including feed pelleting, offer encouraging results, but more research is required to develop cheap, efficient, nutritionally-balanced rations composed completely of local ingredients.

Résumé

L'utilisation des fertilisants organiques et inorganiques et des aliments en pisciculture en eau chaude en Afrique est revue.

La composition des différents fertilisants et aliments est presentée ainsi que leurs avantages et leurs inconvénients. L'usage du chaulage est discuté. L'utilisation des fertilisants inorganiques, semblent limité dans la plupart des pays de la région ceci étant du aux faibles disponibilités et aux prix élévés. Cependant l'index de profit possible avec une culture avec fertilisant inorganique ou bien avec des aliments semble être le même, respectivement, 5.73 et 6.06. L'utilisation de fertilisants organiques tel que manure et composte ne semble être utilisé que dans les étangs des familles rurales. Mais des élevages associés tels que élevage de porc au dessus des étangs, offrent un systême de fertilisation organique directe. Cette méthode devient populaire.

La quantité, la qualité des produits pourant servir d'aliments pour les élevage de poissons semble augmenté en Afrique. Malgré cela l'efficacité de la plupart des élevages de poissons et principalement de la monoculture de tilapia reste faille.

Des recherches plus importantes doivent être entreprises pour développer de meilleurs méthodes de culture de tilapia utilisant des fertilisants et des aliments. Des élevages en polyculture doivent être essayes et donc beaucoup d'effort de recherches doivent être fait pour évaluer les potentialités des espêces locales.

Les efforts d'application des techniques modernes d'alimentation, comme la fabrication d'aliments sec, donnent des résultats encourageants, mais des recherches supplémentaires doivent être faites pour produire des rations peu couteuses, efficaces et bien equilibrées, à partir de produits locaux.

1. INTRODUCTION

1.1 Background

Expansion of warm-water fish culture on the African continent involving the use of techniques of fertilization and feeding began in the early 1950's. During this period literally thousands of small, subsistence-level fish ponds were constructed in many countries with colonial assistance (Meschkat, 1967). Government breeding centres were responsible for developing suitable fish culture methods and supporting the rural fish pond development programmes. In spite of a flourishing start, fish culture in Africa entered a period of limited activity during the 1960's.

Reasons cited by FAO (1967c) for this disillusionment in fish culture were over-ambitious fish culture programmes and poor efficiency of fishery services, especially in extension work. In at least some countries interest was rapidly lost because farmers had been obliged to build ponds. Meschkat (1967) cited difficulty in controlling overpopulation of the prolific tilapia, the principal fish cultured, as one reason for the declining interest. Vincke (1974a) observed that the causes of decreased interest in fish culture were: 1) lack of welltrained extension personnel specialized in fish culture; 2) lack of basic fish culture techniques adapted to local conditions due to little ground work in Africa; 3) ponds with poor water quality not fertilized nor fed offered discouraging results to many farmers, and 4) construction of many family ponds was poor (undrainable small ponds) and often badly located. Even with profound problems of protein deficiency, traditional food habits and ethnic and socio-economic patterns have often hampered the development of fish culture.

As late as 1967, with only a few exceptions, subsistence fish culture in Africa had not yet been expanded into commercial-scale fish farming, and the use of fertilizers and feeds, up to this time, was mainly limited to government fish culture centres where basic research was beginning.

This review is an effort to present a critical analysis of available information on fertilization and feeding practices in warm-water pond fish culture in Africa, including a discussion of gaps in technical knowledge and suggestions of guidelines for future action. Publications and other sources of information for this paper were limited due to time and location of the author.

1.2 Review of Material Presented at 1966 FAO Symposium on Warm-Water Fish Culture

The 1966 FAO World Symposium on Warm-Water Pond Fish Culture placed African fish culture into perspective up to that time. Many of the conclusions drawn at this conference may still, in general, be in effect for the region. For example, van der Lingen (1967) noted that little critical work had been carried out on the effects of fertilizers on the biological cycle of ponds in Africa; very few investigations had been made on a statistical and scientific basis. FAO (1967a) reported serious doubts concerning the feasibility of artificial feeding in Africa. The absence of a traditional animal husbandry and the poor economic status of most rural farmers were cited as reasons why artificial feeding was not widely accepted. Even though feeding practices had been introduced by extension workers in rural subsistence fish culture, Meschkat (1967) observed that feeding was not done at all or, at least, not regularly. Lemasson and Bard (1968) reached similar conclusions. In subsistence “home-ponds” where feeding was practised it was limited to the most easily available feeds such as cassava leaves, cotton seed, beer wastes, etc. The use of inorganic fertilizers was not recommended in such rural home-ponds due to limited availability and high cost. Meschkat (1967) noted that fish culture is often neglected, for much of the year in many cases, by the subsistence fish farmer in favour of land cultivation. He suggests the lack of development of specialized trades associated with fish culture, as is found in Asia, is a limiting factor in the development of commercial fish farming. Van der Lingen (1967) discussed the use of lime, organic and inorganic fertilizers, as well as green manures in African fish culture, and concluded that further investigation is needed on the effects of fertilizers on all biological phases culminating in fish production.

1.3 Limitations of Past Work

Often results of fertilization and feeding studies conducted at government stations in Africa draw conflicting conclusions. Reports of research on fertilization often lack important information on soil and water chemistry. The African region is very large, and great differences exist in climatic conditions and in the chemistry of soils and water from one area to another, facts which lend themselves to conflicting results. Some studies have been poorly planned. For example, a study to evaluate the effects of fertilization on fish production is rendered useless when “occasional feeding” is permitted; effects of fertilization are masked by feeding in this case. In some cases fertilization and feeding trials have been conducted with new species whose biology and growth characteristics in ponds were not fully known, thus, limiting the value of such studies.

Criticism may be made of feeding studies conducted in very small ponds (0.01–0.04 ha) with extrapolated results expressed on a hectare basis. Exaggerated production figures reported from such studies have never been duplicated in larger ponds, and such results should only be regarded as encouraging and preliminary. Workers should be cautioned in the manner in which they report such findings. To validate findings three repetitions of any study or treatment are desirable.

In general there exists a limited understanding on the effects of fertilization and feeding in culture of tilapia in Africa. Little work has been done with other species. African workers have relied heavily on work conducted in Europe, America and the Far East. Although Bardach et al. (1972) caution against the direct application of such studies in Africa, these studies have stimulated careful research. Examples are fertilizer trials recently carried out in the Ivory Coast at the Fish Culture Research and Training Center of the Centre Technique Forestier Tropical (C.T.F.T.) in Bouake (Lazard, 1973) and feeding trials in the Central African Republic by the FAO Regional Project at Bangui.

1.4 Outlook

In view of current fish culture research activities on the continent, optimism may be forecast for the future of fish culture in Africa, in spite of past fluctuations in interest and the many constraints to its development. Although some twenty years of fish culture programmes have offered only limited encouragement, current projects in several countries offer promise. Efforts in fish culture extension by the United States Peace Corps in West Cameroon have had a significant impact on rural farmers through introduction of mirror carp and feeding practices. New species of fish are being evaluated for culture, and projects of commercial scale are implementing advanced techniques for intensive fish production methods. The FAO has made impressive progress in these areas in Central African countries through work on the fast-growing Clarias lazera and studies on feeds and fertilization. The use of fertilizers and feeds will play a major role in the development of fish culture in the region during the next decade. Although actual rising costs may virtually prohibit the use of inorganic fertilizers in many countries, possibilities remain in the use of organic fertilizers which will become more available with continued development of animal husbandry. High-quality food stuffs for feeding fish are limited in Africa, but development of agriculture in general will bring about production of more by-products suitable for fish feeds. It appears that fish culture can successfully compete with other forms of animal husbandry for these food stuffs.

Results and conclusions of work completed since 1966 on the use of fertilizers and feeds in warm-water fish culture in Africa are briefly reviewed below.

2. LIME

The use of lime in fish ponds in Africa is limited, and workers throughout the continent have reported variable results (van der Lingen, 1967). Similar conflicting findings have been obtained in Europe (Schaperclaus, 1962) and the United States (Swingle, 1947); however, most workers agree that productivity is greater where substantial amounts of calcium are present (Hickling, 1962). Many of the soils and waters in Africa are acid and, thus, deficient in calcium. In such instances application of some form of calcium should be beneficial.

2.1 Benefits of Use of Lime

Foremost among the beneficial effects of lime in fish ponds is: 1) raising the pH of acid water to neutrality, thus, establishing a strong alkaline reserve or pH buffer system and making the water more productive. This serves to increase the effects of application of inorganic fertilizers as noted by Hey (1952). Other beneficial effects include: 2) providing a reserve supply of CO₂; 3) the acceleration of the decomposition of organic matter; 4) the stimulation of base exchange action and bringing about of liberation of absorbed nutrients, such as phosphates, in bottom muds; and 5) serving as a disinfectant. These major forms of lime are available: quicklime or CaO (60–71 percent of CaO), agricultural lime or Ca(OH)₂ (45–54 percent CaO) and ground limestone or CaCO₃ (30–40 percent CaO). The latter is called dolmite when magnesium is present. Other minor sources of calcium include basic slag, calcium cyanamid, calcium sulphate and calcium nitrates.

2.2 Studies on Lime Prior to 1966

Van der Lingen (1967) summarized findings of various workers on the use of lime in Africa up to 1966. He reported that South African workers found the use of lime valuable, noting that Lombard (1959) recommended application of agricultural lime at a rate of 900 kg/ha spread on the dry pond bottom. He commented on work completed in Rhodesia by Mortimer (1961) who recommended 1 675 kg/ha spread on the water at monthly intervals for ponds with soft water. Benefits to fish production through such applications were not presented. Huet (1957) noted that the cost of application of lime was a negative factor in its use in Zaïre. Contrary to other workers' findings, Charpy (1956) found fish production in water with a high lime content to be similar to that in water with a low lime content. In waters of pH 6.8–6.9 in the Ivory Coast the C.T.F.T. (1967) reported fish production up to 664 kg/ha/yr with agricultural lime applied at 500 kg/ha every two months. The use of lime was discontinued, however, as the gains obtained in fish production were offset by the high cost of liming. Similar conclusions on the use of lime were drawn in Madagascar (C.T.F.T., 1966).

In Zambia, Strum (1965–66) conducted studies on effects of phosphates, lime and cut vegetation on fish production in waters of pH 6–7. With an initial application of lime at 1 500 lb/acre (1 800 kg/ha) followed by monthly applications of 250 lb/acre (300 kg/ha), he found few beneficial effects on fish production and observed that lime may precipitate phosphate in increasing the pH. Similar findings were reported by Hepher (1958a and b). Van der Lingen (1967) suggests that the value of liming may be through a variety of interactions and that high applications after the initial dosage may not be required; once soils are rendered neutral the continuous use of lime is at best unnecessary and at worst detrimental.

The use of lime in waters of pH lower than 6.5 appears to increase fish production, although it may not be economical. The use of lime in waters of pH greater than 6.5 appears unnecessary. But few studies have been made on the effects of lime alone on fish production in Africa. In Malagasy Republic in 1965 and 1966, Vincke (personal communication) conducted detailed studies on the effects of lime on zooplankton production, including complete soil and water chemistry analysis. Results were very heterogeneous, and it was concluded that, although lime increased pH, its effects were irregular and temporary (C.T.F.T., 1966). Research has been conducted on the effects of applications of various inorganic fertilizers and lime on the survival of fry of common carp, Heterotis niloticus and other species. Interpretation of results is difficult in such research; poor survival may be due to temperature, handling, density of stocking, parasites or disease or any of a number of other factors and have no relation to the application of a particular mix of fertilizers. Perhaps conflicting results on the use of lime could be clarified with new studies using lime alone accompanied by complete chemical analysis of soil and water. Such information is lacking in reports of many African workers. The following is a brief summary of the limited amount of work completed on the use of lime in Africa after 1967.

2.3 Liberia

At the Suakoko fish station in Liberia in ponds with acid soil and water (pH 4.5–6.0) Vincke (1972) recommended the use of 1 665 kg to 2 225 kg/ha of lime spread over the pond bottom. Results on the effects of such applications on fish production were not available.

2.4 Malagasy Republic

Studies completed in the Malagasy Republic by Vincke (1970a and 1971) on the influence of N:P:C:a on survival of carp fry indicate that nitrogen alone had little effect. The best results, 53.2 percent mean survival, were obtained with a mix of triple superphosphate at 40 kg/ha, agricultural lime at 120 kg/ha and ammonium sulphate at 80 kg/ha applied in equal amounts at the beginning and the middle of a thirty-day growing period starting with three-day-old fry. Another study yielded 96.9 percent mean survival after thirty days with triple superphosphate at 20 kg/ha, agricultural lime at 30 kg/ha and ammonium sulphate at 40 kg/ha. Controls without fertilizers in this study yielded 53.3 percent mean survival, equalling the best results obtained with fertilizer in the first study cited. Each of the treatments in each of these studies had at least two replications but variation within treatment was not presented.

2.5 Other Countries

Although Sivalingam (1974c) and other authors indicate lime is used in fish ponds in Nigeria, they present no information on rates of application, costs or effects on fish production.

For Central East African countries Maar et al. (1966) noted that the amount of lime required depended upon degree of soil acidity. Although they indicated it is difficult to give figures for liming due to high variation of soils and waters, they presented the following information as a rough guide.

1. New ponds:

   1. Clay soils: 1 500 to 2 000 lb of lime per acre (1 680–2 240 kg/ha on the bottom when the pond is dry, lightly worked in if possible

   2. Sandy soils: 1 000 to 1 500 lb of lime per acre (1 120–1 680 kg/ha on the bottom

2. Once a year after draining for cropping:

   1. Clay soils: 1 000 lb of lime per acre (1 120 kg/ha)

   2. Sandy soils: 500 to 1 000 lb of lime per acre (560–1 120 kg/ha) on the bottom

They further recommended the monthly application of lime at 150 to 200 lb/acre (161–224 kg/ha) in small ponds where intensive feeding and manuring is being done, unless the inflowing water is very rich in calcium. They cautioned against the application of lime at the same time phosphate fertilizers were being applied.

3. INORGANIC FERTILIZERS

The application of inorganic fertilizers in fish ponds has been shown to increase fish production substantially in Africa as in Europe, North America and Asia. Studies on the use of fertilizers by African workers have confirmed some of the classic findings of Swingle (1947), Schäperclaus (1962), Hickling (1962) and others, these being that phosphorus has been shown to be the most limiting element in fish ponds, and nitrogen and potassium may or may not be required for fish production. However, fertilizer use has not been perfected enough to give predictable results under all conditions, and recent severe increases in the price of fertilizers may greatly limit their use in Africa. Nevertheless, where agricultural by-products for fish feeds are in limited supply, as in Africa, fertilization provides the second best means for increasing fish production, provided costs are not prohibitive.

Essentially, all fish production is based on plants (especially phytoplankton), directly or indirectly. The use of N:P:K fertilizers by plants in water is similar to that of land plants. Phosphorus has been shown to be the single most limiting fertilizer component in fish production. It is very active and is found in very small amounts in solution.

Nitrogen is the second most important element, although its continued use may not be necessary in ponds receiving nitrogenous fertilizers over several years, especially in the tropics where high rates of nitrogen fixation occur in ponds. The same appears true for potassium. Swingle (1965) demonstrated this in Alabama ponds and found he could reduce fertilizer costs by 70 percent without loss in fish production with applications of phosphorus only in ponds having received complete fertilizers (containing all three basic plant food elements, N:P:K) over several years.

3.1 Factors Influencing Effects of Fertilizers

According to Snow et al. (1964), factors affecting the influence of fertilizers on fish production may be classed as physical, biological and chemical. Physical factors include the depth of the pond, the amount (development) of shoreline, size of the pond, rate of water exchange, turbidity of the water and water temperature. Biological factors include species and type of plant life present, animal forms present and the feeding habits of fish present. Chemical considerations include the elements already present in the water supply, the composition of the bottom mud, pH, amounts of calcium and magnesium and interaction between ions or radicals present.

3.2 Benefits from Use of Fertilizers

In properly constructed, well-managed ponds benefits to be obtained from the use of inorganic fertilizers in fish culture in Africa include: 1) stimulating the growth of natural fish food organisms (plankton); 2) increasing fish production; 3) controlling undesirable rooted aquatic plants and, consequently, 4) controlling or reducing mosquitoes and snails. In Africa where malaria and schistosomiasis are serious health hazards control of mosquitoes and snails is very desirable.

3.3 Past Work

Van der Lingen (1967) and FAO (1967b) summarized the use of inorganic fertilizers up to 1966, stressing the role of pond soils in fertilization. Three types of pond soils were discussed with suggestions on use of fertilizers for each. Peaty soils found in swampy areas are generally very acid and deficient in calcium, magnesium and potassium. The use of lime and magnesium were recommended to combat acidity in such soils. Ponds built in cat clays offer a unique situation. Such soils are unproductive and even toxic for agricultural crops due to a high content of aluminium sulphides and iron. But when limed, flocs of hydroxides form, isolating the soil from the water; consequently, the water is quite productive when fertilized with phosphates. Ponds built in alkaline or marl soils are low in fertility due to precipitation of iron or calcium phosphate and low organic contents. Application of organic manures was recommended for such pond soils. Overall, the use of phosphates was highly recommended with frequent small applications preferred over one large dose. The need for nitrogen fertilizers in the tropics where high levels of nitrogen-fixation occur was questioned. The use of potassium fertilizer in fish ponds may not be necessary as can be determined from analysis of soil and water for nutrient requirements.

Van der Lingen (1967) reported increased fish production up to four times that of natural production with lime and phosphate fertilizers in the Transvaal. Lombard (1959) compared production by this method with production obtained through artificial feeding. Fertilizers used were 19 percent superphosphate applied in annual applications of 185 kg/ha or 225 kg/ha of basic slag. Hey (1952) recommended use of N:P:K fertilizers in the ratio 1:2:1 applied at 224 kg/ha initially and thereafter at approximately monthly intervals to maintain a green-brown colour and transparency of less than 30 cm. This compares with methods used in Alabama by Swingle (1965) who recommended use of 8:8:2 grade N:P:K fertilizer applied at 100 lb/acre (112 kg/ha) as needed to maintain a phytoplankton “bloom” dense enough to limit visibility to a maximum of 45 cm. With this method phosphates were applied at an annual rate of about 81 kg/ha or 9 kg/ha/month between February and September. Maar (van der Lingen, 1967) recommended a similar method in the use of N:P:K fertilizer at a grade of 8:8:4 applied at approximately 220 kg/ha as an initial application and thereafter as suggested by Hey. In making the mixture he used sodium nitrate in soft waters and ammonium sulphate in hard waters.

Van der Lingen (1967) reported the use of basic slag applied at 36 kg/ha at monthly intervals as standard procedure on an experimental farm near Jos, Nigeria.

Two reports on different methods of applying fertilizers were discussed by van der Lingen. In Zambia studies were conducted applying granular double superphosphate (30 percent) by three different methods-spread on the surface, applied in floating perforated cannisters and applied in solution. The concentration of phosphorus after four weeks was considerably higher in ponds receiving phosphorus in solution; application by floating cannisters gave better results than by surface spreading. Results in Rhodesia on phosphate fertilizer applied in hanging sacks in water support this last finding (van der Lingen, 1967).

3.4 Sources of N:P:K Fertilizer Components

Sources of N:P:K fertilizer components are presented in Tables I-III as complied by Snow et al. (1964).

TABLE I
Nitrogen fertilizer sources with chemical formulas, percent nitrogen and other elements.
(from Snow et al., 1964)

Percent Other Elements: ^a 73.0 - P₂O₅
^b 48.0 - P₂O₅
^c 48–52.0 - P₂O₅

TABLE II
Potassium fertilizer sources with chemical formulas, percent K and percent of other elements.
(from Snow et al., 1964)

Percent Other Elements: ^a 14 - N₂

TABLE III
Phosphate fertilizer sources with chemical formulas, percent P₂O₅, percent of other elements, and availability.
(from Snow, et al., 1964)

Percent Other Elements: ^a 17 - N₂;
^b 40 - CaO, 3 - Mg and Mn;
^c 21 - N₂;
^d 11 - N₂;
^e 35 - K₂O

The following is a brief summary of available information on work completed after 1966 on the use of inorganic fertilizers in Africa.

3.5 Gabon

Studies were conducted at the Oyem fish culture research centre during the FAO regional project, 1967–1972, to compare triple superphosphate (45 percent P₂O₅) and basic slag (15 percent P₂O₅) containing 40 percent CaO and 3 percent Mg and Mn. Basic slag (Scories de Thomas) applied every two weeks at 600 kg/ha increased natural fish production 400 kg/ha. These results were better than those obtained with triple superphosphate applied at an equivalent rate. Other results were heterogeneous and no direct relation was found between the amount of fertilizer used and fish production obtained. Studies were handicapped due to seepage from ponds and a low pH of 6.0. Since better results were obtained with basic slag which contains lime, it appears that liming would be beneficial at the Oyem station.

3.6 Ivory Coast

Research in the use of inorganic fertilizers has been conducted at the Centre Technique Forestier Tropical's fish culture training centre in Bouake since the early 1960's. The C.T.F.T. (1967) reported a 100 percent increase in fish production in ponds fertilized with 133.3 kg/ha triple superphosphate and 238 kg/ha of ammonium sulphate applied monthly during a four-month production period. Either of the fertilizers applied alone gave an increased production of 50 percent. However, costs were excessive.

Studies completed during 1970–1971 on the lasting effects of triple superphosphate (45 percent P₂O₅) indicated that single applications of 20, 40, 80 and 120 kg/ha had effects lasting 7, 14, 21 and 25 days, respectively. Further studies on the rate of application of triple superphosphate indicated an optimum dose between 55 and 66 kg/ha/month (C.T.F.T., 1971). Fish production up to 1 750 kg/ha/yr was obtained with triple superphosphate applied at 60 kg/ha/month in ponds stocked with tilapia hybrids at 110/are (100 m²). Results obtained were economically feasible, but this has not been demonstrated in large commercial-size ponds.

Lazard (1973) was inspired by work completed in Malacca by Prowse in which a mean production of 1 462 kg/ha/yr was obtained with application of 25 kg/ha/month of triple superphosphate equal to 11.21 kg P₂O₅/ha/month. They found that up to this rate of application a linear relationship existed between amount of phosphate applied and fish produced. Based on past results from Bouake, Lazard applied triple superphosphate at 60 kg/ha/month in 6 four-are, unlimed ponds of pH 7.0. Three unfertilized control ponds were maintained. The monthly dose was given in two equal applications in baskets suspended in the surface waters of the ponds. Tilapia hybrids were stocked at 1/m² with one Latus niloticus per pond. During the six-month study water quality analyses were regularly determined for alkalinity, pH, phosphates and iron. Results in treated ponds ranged from 1 257 to 2 230 kg/ha/yr whereas results in control ponds ranged from 683–702 kg/ha/yr.

The study was economically feasible. Actual incidence of the cost of fertilizer per kg of fish produced in the study was CFA.F. 18.9(CFA.F. 233 = U.S.$ 1.00) using superphosphate (21 percent P₂O₅) at a cost of CFA.F. 20/kg.

Conclusions drawn from this study were:

1. Alkalinity was not affected by addition of phosphate;

2. When the equivalent of 40 kg triple superphosphate was added presence of phosphates was found in the water for 15 days after application. Phosphates increased as the study continued. Similar results were found with iron;

3. The pH increased during the study, as did phytoplankton growth;

4. The equivalent of 27 kg P₂O₅/ha/month had a highly significant effect on production.

3.7 Liberia

Vincke (1972b) reported the use of 15:15:15 (N:P:K) fertilizer with two applications in the dry season at 25 lb/acre (28 kg/ha). One application was made at the beginning of the dry season in November, and an equal dose was applied in December-January. At a cost of U.S.$ 0.76/lb (U.S.$ 0.167/kg) the annual cost of fertilizer per acre was U.S.$ 3.80 (U.S.$ 9.90/ha/yr). Results of such fertilization were not presented. The use of other fertilizers was discussed for application in ponds where fish were raised in conjunction with rice.

3.8 Malagasy Republic

Inorganic fertilizer trials have been conducted in the Malagasy Republic, often in parallel with studies in Bouake, Ivory Coast. A study was undertaken in 1967 to evaluate the influences of different fertilizer elements (N:P:K:Ca) on fish production. However, according to the C.T.F.T. (1967), effects of fertilization were masked due to feeding permitted during the study. Research was conducted in 1969 on the lasting effects of P and N in unstocked, fertilized ponds. Vincke (1969) reported levels of phosphate varying between 1.5 and 3.0 mg P₂O₅/l in untreated ponds. Two days after application of triple superphosphate at rates of 60, 120, 200 and 300 kg/ha the concentration of P₂O₅ varied from 4.25 to 7.0 mg/l and decreased to 2.0–3.0 mg/l 30 days after treatment. Concentration of P₂O₅ was inconsistent with the level of fertilizer applied. It was concluded that the effects of one application of phosphate lasted three to four weeks, and the best rate of application was 120–150 kg/ha/month.

Application of ammonium sulphate at the same rates as phosphate quoted above resulted in concentration of NH₄ varying between 0.25 and 4.0 mg/l with nitrates reaching a maximum of 2 mg/l. Fifteen days after application no trace of nitrogen was detectable. The most desirable application rate of ammonium sulphate was 150–200 kg/ha/15 days.

This same study was expanded to evaluate the effects of fertilizer treatments on growth of carp. Based on fish production, the treatments in decreasing order of production were 300 kg of triple superphosphate, 200 kg triple superphosphate and 60 kg of ammonium sulphate.

In considering the economics of the study, Vincke (1969) applied the following formula:

Applying this to results of each treatment he found costs too high - the cheapest application of triple superphosphate being 60 kg/ha at a cost of F.MG. 98.75/kg (F.MG. 233 = U.S.$ 1.00) of fish produced and 60 kg of ammonium sulphate at F.MG. 58.81/kg of fish produced.

In 1970 Vincke (1970a) reduced rates of application of triple superphosphate to 20, 40, 80 and 160 kg/ha and ammonium sulphate to 40, 80, 160 and 320 kg/ha. Again, costs were prohibitive at the higher rates of application. Effects of a single application of phosphate fertilizer lasted 15–21 days, and the highest ammonium sulphate application lasted 40 days. Recommended application of triple superphosphate was between 20 and 40 kg/ha given biweekly and ammonium sulfate was between 40 and 80 kg/ha given every two to three weeks. The incidence of the cost of fertilizer per kg of fish produced varied between F.MG. 64.73 and 93 (F.MG. 233 = U.S.$ 1.00).

Later Vincke (1970a and 1971) reported fertilizer trials studying the effects of fertilizers on carp fry survival. He applied triple superphosphate at 40 kg/ha, ammonium sulphate at 80 kg/ha and agricultural lime at 120 kg/ha, singly and in mixes. Combinations of triple superphosphate mixed with lime and triple superphosphate mixed with ammonium sulphate and lime gave the best survival results - ranging from 46 percent to 67 percent. Such studies testing the effects of fertilization on survival of fry include many variables. Poor fry survival in one treatment may be due to parasites or disease, poor initial handling of fry, insect predation and other factors having little to do with effects of fertilization. Therefore, caution should be used in evaluating such studies.

A study to evaluate methods of application of triple superphosphate at 20 kg/ha in carp fry ponds was undertaken in 1972. Two methods were compared-surface broadcasting and application in baskets suspended in the surface waters. Chemical analysis including temperature, pH, alkalinity, iron and phosphate were made regularly throughout the six-month experiment. Results indicated little difference in chemical parameters between the two treatments except for a higher alkalinity which persisted in ponds treated with phosphates in baskets suspended in the surface waters. Comparing the methods of application by broadcast and basket, the incidence of the cost of fertilizer per kg of fish produced was F.MG. 7.85 and 10.30, respectively. The broadcast method also produced significantly larger carp than the basket method. Vincke (1972a) concluded that, although some differences existed in the results obtained, neither method was superior to the other from a production standpoint. These results contradict those obtained in Zambia and Rhodesia (van der Lingen, 1967) and in Alabama by Swingle (1965) who obtained best results by applying fertilizers off platforms 30 cm under water. However, the different feeding habits of the species used and differences in climate probably account for the different findings.

During 1971 and 1972 studies were conducted to determine the most desirable economic mix of N:P:K:Ca fertilizers for use in carp fry production. Results obtained from these studies were heterogeneous but the following conclusions were drawn:

1. Treatments including lime at 30 kg/are/three weeks (3 000 kg/ha/three weeks) gave consistently better results than treatments without lime;

2. Concerning the incidence of the cost of fertilizer per kg of fish produced, a mix of triple superphosphate at 20 kg/ha and agricultural lime at 30 kg/ha applied every three weeks gave the most favourable economic results - F.MG. 67.93/net kg of fish;

3. Ammonium sulphate alone has little effect on fish production;

4. Lime plays an important role in improving production when used in combination with N and P fertilizers; however, it has little influence on production when used alone. Vincke (1972a) called attention to the fact that his conclusions were drawn for conditions in the Malagasy Republic and may not apply elsewhere.

3.9 Nigeria

Van der Lingen (1967) reported the use of basic slag at 36 kg/ha and phosphates at 1 500 kg/ha at an experimental farm near Jos. Sivalingam (1974a and b) indicated fertilizers were used at government fish culture centres but that their use was very limited in private ponds. Although reference to specific fertilizers was not made, Sivalingam (1974c) summarized fish production in fresh and brackish water as indicated in Table IV.

TABLE IV
Summary of fish production in Nigeria, 1974.

Fertilizers used were phosphate, ammonium sulphate and lime. Specific rates were not included.

3.10 South Africa

Bardach et al. (1972) reported a four-fold increase in production of Tilapia mossambica in ponds receiving 185 kg/ha of 19 percent superphosphate in conjunction with lime. Similar results were obtained with basic slag applied at 225/kg/ha. They cited an increase in production of 240 kg/ha over natural production of Tilapia melanopleura in ponds receiving 19 percent superphosphate at 330 kg/ha during a five-month production period.

3.11 Zambia

Strum (1965–1966) reported on fertilizer trials conducted at the fish station near Kitwe. Tests were conducted to evaluate 38 percent superphosphate alone and in combinations with lime and cut grass in tilapia production ponds. Results are summarized in Table V.

From these results and others, Strum concluded application of phosphates in soft water definitely increases fish production. Application of lime offered little benefit and can possibly cause precipitation of phosphates. The use of fresh cut grass offered no benefit in increasing fish production.

Bardach et al. (1972) noted that FAO biologists recommended the use of 50 kg/ha/month of double superphosphate or 100 kg/ha/month of basic slag in polycultures of tilapias and Haplochromis mellandi.

3.12 Other Countries

The use of inorganic fertilizers has been reported in other countries in conjunction with rice-cum-fish culture. Such programmes are presently underway in Ghana and Dahomey. Fertilizers are used in still other countries for which information was unavailable, notably, Zaire, Congo, Malawi and Rwanda. In Central East Africa, Maar et al. (1966) recommended the use of superphosphate at 100/lb/month (56 kg/ha/month). Torrans (1973) reported the use of 100 kg/ha of 45 percent superphosphate applied in bags or baskets suspended in the water to improve “bloom” in ponds in Cameroon. In the United Arab Republic, Wahby (1974) studied the water chemistry of ponds fertilized with superphosphates at 25 kg/ha/month and ammonium nitrate at 25 kg/ha/month. Although effects on fish production were not presented, he observed that both phosphorus and nitrate concentrations returned to a preapplication level seven days after application.

TABLE V
Results in evaluating 38% superphosphate, lime and cut grass applied in tilapia production ponds

4. ORGANIC FERTILIZERS

The use of organic fertilizers in fish culture in Africa appears limited at present, although the combination of animal rearing with fish culture is increasing in popularity. Sources of organic fertilizers for use in fish culture, although limited due to poorly developed animal husbandry practices, include various animal manures mainly from pigs, cattle, chickens and ducks. Slaughterhouse wastes (dried blood, cow stomach contents), cassava peels, compost and brewers' wastes are also useful organic fertilizers. Residues from fabrication of oil from peanuts, palm nut, etc. are also usually available (C.T.F.T., 1972a). Use of such by-products depends mainly upon local availability at a minimal cost and existence of adequate transport facilities. From available information the use of such organic fertilizers appears limited to small, subsistence, family-type ponds and large-scale employment of organic fertilizers in commercial-size ponds is very limited due to unavailability of large quantities of materials.

This section concerns the use of organic fertilizers and waste products applied to ponds from sources apart from fish culture and does not concern the increasingly popular combination with animal rearing, such as pigs or ducks, in enclosures built beside or over fish ponds. Such combinations, long popular in Asian fish culture, have produced up to 10 000 kg/ha/yr of fish with only excrement and waste feed from the animals going into the pond (FAO/UN, 1973c). This technique is the subject of a separate review paper.

4.1 Advantages and Disadvantages in Use of Organic Fertilizers

According to Huet (1970), Snow et al. (1964) and the C.T.F.T. (1972a), the advantages from use of organic fertilizers are:

1. A shorter production cycle is possible than that obtained with inorganic fertilizers, especially for production of zooplankton in fry-rearing ponds;

2. Plant growth (natural fish foods such as phytoplankton) is increased through decomposition of organic materials and subsequent release of carbon dioxide;

3. Organic fertilizers aid in the clearing of heavily silted pond water;

4. Some organic fertilizers serve as a supplemental fish feed;

5. Organic fertilizers exert a favourable action on pond soils.

Disadvantages in the use of organic fertilizers are:

1. Due to the quantities required, they may be a more expensive source of plant nutrients than inorganic fertilizers, depending on the country involved;

2. They may deplete oxygen supply in the water;

3. They may stimulate the growth of undesirable filamentous algae;

4. More labour is required for application of organic fertilizers than for inorganic fertilizers;

5. If applied in excessive quantities organic fertilizers may create conditions favourable to fish diseases and parasites.

In general the application of organic fertilizers to fish ponds stimulates plankton growth and has been shown to increase fish production several times over natural production. Use of such materials in relatively sterile, newly-built ponds is especially beneficial as conditioners of pond soils in increasing organic matter.

Hickling (1962) stated that the benefits obtained from use of organic fertilizers are greatly lessened in old ponds with formed bottom muds. He noted the more practical use of inorganic fertilizers. The application of seven t of cow manure in a one-acre, limed pond (7 840 kg/ha) in Malacca increased fish production two times over untreated ponds. However, the same results were obtained with only 50 lb of triple superphosphate (56 kg/ha). Hickling observes that in countries where soils are very poor in organic matter, the use of manures is better utilized on the soils in farming the land rather than in fish culture. In using pig manures in Germany, Schäperclaus (1962) obtained an extra 30–40 kg of fish/t of manure applied.

In considering organic fertilizers it is customary to ignore all elements except nitrogen due to the low phosphorus and potassium content. Snow et al. (1964) noted the relative unavailability of organic phosphorus and potassium for plant growth from organic fertilizers. A high availability of nitrogen from such fertilizers, however, certainly aids in mineralization of organic matter. The composition of various organic fertilizers for use in Africa is summarized in Table VI, taken from Snow et al. (1964), Hickling (1962) and other sources.

Several authors recommend the combined application of organic and inorganic fertilizers. This technique, although somewhat costly, has advantages for use in fry-rearing ponds where drainings are frequent and only limited time is available for development of an adequate food supply.

TABLE VI
Percent composition of various organic fertilizers for use in fish culture in Africa

4.2 Summary of Work up to 1966

Meschkat (1967) and van der Lingen (1967) summarized the use of organic fertilizers in Africa up to 1966. Meschkat stated that although organic and inorganic fertilizers had been shown to increase tilapia production considerably greater benefits were obtainable with their use in carp ponds. This difference is, in part, explainable by the bottom feeding habits of carp which undoubtedly facilitate mineralization of organic matter in bottom muds, thus, releasing nutrients and increasing productivity. In South Africa Hey (1952) recommended the use of 2 t/ha of horse or cattle manure or 500–1 000 kg/ha of poultry manure. Van der Lingen (1967) noted that in Central Africa, de Bont favoured the use of waste grain, cereals and other by-products over manures. With as much as 10 t/ha of mill sweepings he obtained 5 000–9 000 kg/ha of fish, noting the dual purpose of mill sweepings as food and fertilizer. With manures alone he obtained fish productions of 1 000–2 000 kg/ha. In Central Africa, Maar et al. (1966) recommended the use of pig and poultry manures (duck and chicken) over cattle manures since such large quantities of the latter are required. They recommended weekly application of pig manure at 500–1 000 lb/acre (560–1 680 kg/ha) and 100–200 lb/acre (112–224 kg/ha) of poultry manure.

4.3 Methods and Rates of Application

Due to the slow acting effects of manures and the risk of oxygen deficiency when applied in ponds, most authors recommend applying manures over the pond bottom prior to filling or stacked in piles scattered around the edges of filled ponds. Fortunately, the danger of fish mortalities due to oxygen depletion in Africa is very limited because of the hardiness of most of the fish cultured - tilapia and Clarias lazera. The application of grass as compost in ponds is recommended only in the form of dried hays. Sources and rates of application of various organic fertilizers are variable from country to country.

A brief discussion on the use of organic fertilizers in some of the African countries follows.

4.4 Central African Republic, Gabon, Cameroon and Congo

Results obtained from the FAO Regional Fisheries Project, comprising Central African Republic, Gabon, Cameroon and Congo, indicate that the use of organic fertilizers constitutes one of the best means of increasing fish production in the region. Most of the work on the use of organic fertilizers was conducted at the Oyem Fish Culture Station in Gabon where agricultural by-products suitable for fish feed components are virtually unavailable due to supply and costs.

The C.T.F.T. (1972a) reported on the fermentation of cassava in ponds as a means of increasing fish production. Through fermentation toxic cyanhydrous acid and dissolved salts in bitter cassava are removed making it edible for human consumption and, in the process, fertilizing the pond. Five studies were conducted fermenting 5, 10, 50, 100 and 200 kg/are (500, 1 000, 5 000, 10 000 and 20 000 kg/ha) of cassava tubers for seven days. Results were proportional to the amount of cassava fermented up to 100 kg/are. However, 50 kg/are/week (5 000 kg/ha) was recommended as more practical for villagers. Production of Tilapia nilotica in such ponds reached 3 200 kg/ha/yr and 4 280 kg/ha/yr was obtained in ponds receiving fermentation of 100 kg of cassava. In a practical sense, this technique is ideal for use in small family ponds but impractical for use in large ponds due to the large quantities required.

The use of chicken manures as fertilizer was the subject of other studies in Gabon. The sweepings from chicken houses contained 30–40 percent manure and waste feed, the rest being litter. In a six-month trial, 150 kg of chicken house sweepings were applied monthly per are (15 000 kg/ha) and produced 1 800 kg/ha/yr of Tilapia nilotica. In another trial, using concentrated chicken manure applied at 80 kg/are/month (8 000 kg/ha), a production of 2 330 kg/ha/yr was obtained. The rates of application used in this study are considerably higher than those recommended by other workers such as Maar et al. (1966) who suggest the application of poultry manure at 4.48–8.96 kg/are/month (448–896 kg/ha).

The C.T.F.T. (1972a) reported another study in Gabon on the use of cow stomach contents mixed with blood from a slaughter house. With an initial application of 50 kg/are (5 000 kg/ha) a production of 980 kg/ha/yr was obtained. For the small pond owner who lives near a slaughter house this method would be advantageous. More favourable results were obtained in the Central African Republic where ponds were fertilized and fed with a mix of cow stomach contents, fresh blood and coarse, ground cotton seed in a proportion of 2:1.5:1. Production up to 4 618 kg/ha/yr was obtained in commercial-size ponds. More information on these results is included in the section on feeding.

4.5 Other Countries

Semakula et al. (1967) reported on the use of chicken and cattle manures in Uganda. Nuisance blooms of green algae (Spirogvra and Microcystis) developed, causing limited production. The use of green manures was also tried. A dry pond was planted with beans which were cut when beginning to flower; then the pond was filled. A rapid deficiency of oxygen developed resulting in loss of fish.

Studies reported by Strum (1965–66) in Zambia included the use of fresh cut vegetation in fertilizer trials. The application of such vegetation appeared to have no effect on fish production.

In Kenya, Odero (1974) reported great success in the use of cattle manures in fish culture, but no data were presented.

5. FEEDING PRACTICES

The practice of supplemental feeding of fish in ponds has been in widespread use in Africa since the 1950's. But use of feeds and feed technology has experienced a slow development. With the exception of some government fish culture centres, most feeding has been on an extensive basis in small family ponds. Such feeding has been irregular and limited to a small variety of feed stuffs often of poor nutrient quality. Few efforts have been made to formulate feeds and evaluate them under controlled conditions. Recently, work at the FAO Regional Fish Culture Project in Bangui, Central African Republic, has demonstrated the possibility of obtaining considerable increases in fish production through application of feed formulation innovations and feed processing technology. Still much work remains to be done to develop cheap, readily available and efficient feeds, composed of locally-available components.

The FAO (1967a) expressed serious doubts about the feasibility of artificial feeding of fish in Africa in 1966. At present in some regions in rural Africa feeding still may not be feasible due to lack of feed stuffs, but in most cases some form of feed stuff is available, permitting at least an extensive level of fish culture in small, family-type ponds. However, the situation is changing in populated areas where feed by-products are becoming more available with development of agriculture, and the possibility of commercial-scale fish culture may soon become a reality in at least a few countries.

5.1 Advantages of Supplemental Feeding

Hastings (1968) noted that as natural foods become over-harvested due to intensive stocking or are unavailable due to poor water quality fish will accept artificial feeds as food.

Advantages of supplemental feeding to fish include: 1) faster growth occurs; 2) high densities of stocking are permitted; 3) greater productions are possible; and 4) feeding allows the fish farmer to have regular contact with his fish, permitting early detection of disease problems, etc.

In most cases any level of feeding is beneficial as it supplements natural foods in ponds. This is the case in most subsistence fish cultures in Africa. A more intensive level of fish culture is developing at government fish culture stations in an effort to provide more protein on the continent. New methods being used involve heavy stocking and feeding of fish.

5.2 Factors to Consider in Using Feeds in Fish Culture

From studies conducted at the FAO Regional Fish Culture Training Project in the Central African Republic, Hastings (1973) noted that a combination of several feed stuffs into a ration has greater nutritional value than if the feed stuffs were fed separately. Efforts in composing rations for fish culture in Africa have been almost entirely based upon availability and cost, rather than quality, of feed stuffs. The ingredient comprising the greatest percentage of a ration would be the food stuff found in greatest abundance, and so on. Where an abundance of food stuffs exists, it is, of course, more desirable to compose rations offering a balance of nutritive elements including 25–35 percent protein. Some possible food stuffs, such as palm nut cake, have only a limited nutrient value but can be useful in a mixed ration as a filler or binder.

In using very cheap feed stuffs, such as beer wastes or mixes of various agricultural by-products, economical feed conversions ranging from 3 to 12:1 have been reported. Desirable conversions and high productions have been reported in feeding well-mixed rations composed of several ingredients as discussed further on. In Africa such rations (unpelleted) may be fed dry or moist and broadcast in specific areas of ponds or fed wet in balls. Hastings (1973) noted that low feed conversions were desirable and economical. He suggested the following reasons for the high feed conversions obtained with feeding unpelleted feeds: 1) poor digestibility; 2) poor balance of nutritive elements; and 3) non-ingestion of feeds. Although uneaten feeds act as fertilizers in ponds, this food cycle is indirect, inefficient and may be costly.

Criteria for selection of artificial feeds were listed by Ling (1967) as: 1) acceptability to fish; 2) effectiveness in promoting fish growth; and 3) degree of availability and cheapness. A listing of available feed stuffs and their composition is presented in Table VII.

5.3 Pelleted Feeds

The use of pelleted feeds in fish culture in Africa appears to be limited to the FAO Regional Fish Culture Training Project in the Central African Republic. Although experimental studies at this station have not clearly demonstrated the degree of increased efficiency pelleted feeds yield when compared with unpelleted feeds, many European and American workers agree that pelleted feeds are much more advantageous. Unpelleted feeds may lose much of the nutritious substances present before they are ingested by the fish, and fish may select only the most desirable components of such rations. Pelleting of feeds maximizes the utilization of local ingredients and facilitates formulation of “complete feeds”, containing all nutritive elements necessary for growth. Still, in spite of the advantages of this technology, pelleting of feeds for fish in Africa remains in the experimental stage due to high investment costs, other economic considerations, difficulty in maintaining machinery and a variety of problems uncommon to fully-industrialized countries.

A brief discussion follows on the use of feeds in various countries in Africa.

5.4 Central African Republic

In studies conducted at the FAO Regional Fish Culture Project in Bangui, Hastings (1973) established modern techniques of fish feed technology including feed formulation, stocking of feed elements, grinding, mixing and pelleting. Feeding trials were conducted with Tilapia nilotica and Clarias lazera, using two different rations of 30 percent protein - one with only vegetable protein sources and the other with one quarter of the protein from animal sources. These rations were composed of locally available ingredients, and their composition is presented in Table VIII. Results of two trials in feeding these rations are summarized in Table IX.

Even though a greater production was obtained in feeding the vegetable protein diet, the feed conversion was poorer. But the cost of the animal protein ration is 1.7 times greater than the vegetable protein ration. Animal proteins are costly and limited in Africa. It appears that animal proteins may not be required in rations for intensive culture of tilapias.

TABLE VII
Composition of various feed stuffs for use in fish culture in Africa

TABLE VIII
Composition of two rations used in feeding trials Tilapia nilotica and Clarias lazera

1 Imported products

TABLE IX
Comparison of production results of Tilapia nilotica fed two different rations, 1972

¹ 1 kg of fish sells at CFA.F. 150
² U.S.$ 1.00 = CFA.F. approx.
³ Containing only vegetable protein
⁴ Containing vegetable and animal protein

A study at Bangui on feeding the vegetable protein diet to Clarias lazera stocked at 20 000/ha in a 3.7-are (0.04 ha) pond produced a net production of 421.3 kg during a 201-day feeding trial. Fish production in this pond exceeded 18 000 kg/ha/yr according to the C.T.F.T. (1972). Mean growth per fish per day was 2.9 g, and feed conversion was 3.6. A parallel study feeding the animal protein ration to Clarias was terminated too early in the production period to draw conclusions because of severe pond leakage. Clarias did not adapt to demand feeders as tilapia did, but their rate of growth is, indeed, exceptional.

Results of eight feeding trials with Tilapia nilotica conducted after the above work have not shown similar findings with pelleted feeds. Conducted in ponds ranging in size from 19 to 41 ares stocked with Tilapia nilotica at the same rate, other feeding trials have yielded productions ranging from 1 697 to 5 266 kg/ha/yr (mean 3 486 kg/ha/yr). Feed conversions for these trials ranged from 1.9 to 4.6 (mean 3.45). The less favourable results may be attributed to: 1) seasonal or complete unavailability of various ingredients, especially wheat bran which is no longer imported; 2) discontinuation of use of the vitamin mix; 3) changes in the ration contents lowering the protein to an average of about 25 percent; and 4) breakdowns in pelleting machinery and power supply creating variations in feeding. Since the original work of Hastings, higher prices have increased the cost of the vegetable protein ration components, but with changes in composition the costs remain about the same for the ration.

Four trials conducted in feeding a ration of 66 percent beer wastes and 33 percent of a mix of spoiled feeds of 20 percent protein produced a mean net production of 5 080 kg/ha/yr and a mean feed conversion of 12.7. These trials were conducted in ponds ranging from 31 to 70 ares in area. Cost of this ration is CFA.F.4/kg with an incidence of CFA.F.50.8 of feed cost per kg of fish produced.

Results of three trials in feeding coarse-ground cotton seed yielded a mean production of 4 262 kg/ha/yr with a mean conversion of 8.92. The incidence of feed cost per kg of fish produced was CFA.F. 40.14.

Feed being a wet combination of cow stomach contents, coarse-ground cotton seed meal and fresh blood in a proportion of 2:1.5:1, three other trials yielded a mean net production of 4 309 kg/ha/yr with Tilapia nilotica stocked at 20 000/ha. The incidence of feed cost was CFA.F. 37.6 at a mean feed conversion of 9.4. These trials were conducted in ponds ranging from 31 to 48 ares in area.

5.5 Malagasy Republic

In the Malagasy Republic Vincke (1970) reported on feeding trials with carp using rice bran, corn meal, cassava flour, cooked corn and cooked cassava tubers. Two repetitions of each treatment were included, as well as unfed controls. Carp were stocked at 25/are (2 500/ha) in ponds ranging in area from 80 to 124 m². Fish were fed at 10 percent of the estimated body weight per day during a 90-day production period. Results are presented in Table X. For unaccountable reasons the fish in the control ponds averaged more in weight than fish in fed ponds. Concerning production, the corn treatments gave the most favourable results, followed by cassava flour, cassava tubers and rice bran.

With a kg of fish selling at F.MG. 150 (F.MG. 233 = U.S.$ 1.00) Vincke (1970) considered the incidence of feed cost to be incidental.

5.6 Nigeria

Sivalingam (1970 and 1974) reported on culture of Chrysichthys nigrodigitatus, mullets and tilapias in brackish water ponds. Conversions ranging from 1.5–4.78 were obtained with peanut cake alone as feed. In 1970 a production of 2 100 kg/ha/yr was reported with a conversion of 1.5, using a feed mix of peanut cake, ground corn and cassava gari. The FAO (1973a) reported on production of Chrysichthys stocked at about 5 000/ha in a 20-are (0.2 ha) pond. During a 138-day growth period, fish were fed 2.5 kg/day of a mix of peanut cake, corn, cassava gari and palm oil wastes. A net production of 2 412 kg/ha/yr was produced, the crop consisting of 38 percent catfish and 58 percent tilapias. The cost of feeding peanut cake was reported as becoming prohibitive.

TABLE X
Summary of results of feeding trials in carp production Malagasy Republic, 1970

Other results of feeding trials in Nigeria are included in Table IV.

5.7 Togo

Miller (1969) summarized the use of feeds in tilapia culture in Togo. A 23 percent protein ration composed of spoiled powdered milk (15 percent), millet beer wastes (30 percent), cotton seed meal (30 percent), spoiled corn meal (15 percent) and mill sweepings (10 percent) was fed at a cost of CFA.F. 4.6/kg. The ration was mixed wet; then it was dried before feeding by surface broadcasting. The ration was fed at 3–4 percent of the estimated body weight per day. Production results ranged between 1 400 and 4 700 kg/ha/yr, and conversions ranged between 4.7 and 6.7:1.

5.8 Zambia

Mabaye (1971) conducted a study in Zambia feeding Tilapia mossambica brewers waste and peanut cake in aquariums. He concluded brewers waste was unsuitable as a feed due to fouling in aquariums which resulted in premature termination of his study. In a second study he compared peanut cake with corn meal in rations. He concluded that the combination of peanut cake to corn meal, in a ratio of digestible protein to carbohydrates of 1:2, significantly increases the rate of growth of Tilapia mossambica. The addition of penicillin to the ration as a biostimulant did not produce any significant difference in the rate of growth.

5.9 Other Countries

The feeding of beer wastes in Cameroon was reported by the C.T.F.T. (1972d). A conversion of 12:1 was obtained in trials, but at a cost of CFA.F. 6–7/kg; the incidence of cost of feed was a high CFA.F. 72–84/kg of fish produced. Tondo (1974) reported on feeding carp in Cameroon where a favourable conversion of 1.76 was obtained. Details on feeds used were not present.

In Uganda mirror carp and tilapia hybrids were fed corn at 3–5 percent of the estimated total body weight per day according to Kanyike (1974). Production of 1 200 to 2 300 kg/ha/yr were obtained.

El Bolock and Labib (1967) reported the feeding of cotton seed cake and rice bran in a ratio of 1:2 in the United Arab Republic. Carp were fed at 10 percent estimated total body weight per day and production with fertilization equalled 1 218 kg/ha.

Crass (1969), in South Africa, reported on the feeding of carp off platforms suspended in the water. Other information was not available.