|Region||Average Elevation (m)||Average Rainfall (mm)||Soil||Population (%)||Land (%)||Principal Crops||Quality|
|Imbo||1 100||1 200||Alluvial||.5||.7||Banana, manioc, beans, peanuts, sweet potato, cotton, rice, sugarcane, citrus||Excellent|
|Impara||1 700||1 400||Heavy red basaltic||3.6||6.8||Banana, beans, maize, sorghum, sweet potato, manioc, peanuts, coffee, tea, quinchona||Good|
|Boros of Lake Kivu||1 600||1 200||Shallow, silty-clay||3.9||2.7||Banana, beans, maize, sorghum, sweet potato, manioc, peanuts, coffee||Good to excellent|
|Lava||2 200||1 500||Volcanic||4.1||3.5||Banana, beans, maize, sweet potato, sorghum, peas, potato, pyrethrum, tobacco||Excellent|
|Congo-Nile ridge||2 100||1 600||Acid organic||14.2||17.0||Peas, maize, potato, eleusine, wheat, tea, sun-flower, wood||Average|
|Buberuka||2 000||1 200||Laterised||9.2||7.0||Banana, beans, sorghum, sweet potato, maize, potato, peas, wheat, barley||Good|
|Central plateau||1 700||1 200||Organic (various)||21.5||13.2||Beans, sorghum, maize, sweet potato, banana, taro, yam, coffee, soybean||Good|
|Dorsale granitic||1 500||1 100||Light, gravel||15.4||6.8||Banana, beans, sorghum, maize, sweet potato, yam, taro, peanuts, manloo, coffee, livestock||Average|
|Mayaga||1 450||1 050||Clay from schists||13.3||14.1||coffee, beans, sorghum, maize, banana, sweet potato, manioc, peanuts, soybean||Very good|
|Bugesera||1 400||900||Strongly altered clays||1.9||5.3||Beans, sorghum, maize, bananas, sweet potato, manioc, peanuts, livestock||Poor|
|Eastern plateau||1 500||950||Laterised||9.1||13.4||Beans, sorghum, maize, bananas, sweet potato, manioc, peanuts, coffee||Average N Good S|
|Eastern savanna||1 400||850||Old soils, variable texture||3.4||19.6||Manioc, peanuts, beans, sorghum, maize, sweet potato, livestock, National Park||Very good|
Source: Morris, 1979
(in metric tons)
|63 g/day||50 g/day||100 g/week||50 g/week|
|1973||Butare||594 836||13 700||10 700||3 000||1 500|
|Gitarama||524 830||12 100||9 400||2 800||1 400|
|Ruhengeri||505 806||11 600||9 100||2 600||1 300|
|Kigali||460 281||10 600||8 300||2 400||1 200|
|Gisenyi||406 710||9 400||7 300||2 200||1 100|
|Byumba||405 075||9 300||7 300||2 200||1 100|
|Gikongoro||344 480||7 900||6 200||1 800||900|
|Cyangugu||295 038||6 800||5 300||1 600||800|
|Kibungo||271 068||6 200||4 900||1 400||700|
|Kibuye||250 476||5 800||4 500||1 400||700|
|Rwanda||4 058 600||93 400||73 000||21 400||10 700|
|1980||Butare||721 687||16 600||13 000||3 800||1 900|
|Gitarama||636 752||14 600||11 500||3 400||1 700|
|Ruhengeri||613 671||14 100||11 000||3 200||1 600|
|Kigali||558 438||12 800||10 100||3 000||1 500|
|Gisenyi||493 443||11 300||8 900||2 600||1 300|
|Byumba||491 459||11 300||8 800||2 600||1 300|
|Gikongoro||417 942||9 600||7 300||2 200||1 100|
|Cyangugu||357 956||8 200||6 400||1 800||900|
|Kibungo||328 874||7 600||5 900||1 800||900|
|Kibuye||303 891||7 000||5 500||1 600||800|
|Rwanda||4 924 113||113 100||88 600||26 000||13 000|
Source: Reizer, 1975
Peat consists of organic black deposits composed of the remaining parts of plants, partially decomposed, and accumulated due to bad drainage conditions which inhibit their decomposition. The natural vegetation cover consists of hydrophilic plants and mosses. Peat is acid and deficient in minerals and nitrogen, but has a high carbon content.
Meyer, quoted by Van Wambeke (1961), has studied the reclamation of peaty soils. His main conclusions are as follows:
(i) In the large marshes, where peat up to several metres, sometimes even more than 10 m, is present, reclamation presents severe technical and economic problems, including the irreversible settling (compression) which occurs during drying.
Except for peaty soils enriched locally by volcanic ashes in North Rwanda, the peats are inert, of poor quality, and with a very low mineralisation1 capacity and a C/N ratio of between 20 and 30. Such soils are of no interest for agriculture or fish farming, because of their very low mineral content. This is especially true for the swamps situated at high and medium-high altitudes.
(ii) With regard to the swamps with a peaty layer limited to a depth of 1 to 2 m, or where settling has already occurred, the problems differ according to the region:
In the high altitude swamps surrounded by poor grasslands the soils are cold (11 to 15°C) and very poor. They are generally covered by a vegetation composed of Miscanthidium violaceum. The only economical method of bringing about the rapid mineralisation of these peats is the ‘veenbrandkultuur’, i.e., calcination by fire.
Fertilizing with manure gives good results; liming has irregular effects.
In the swamps of medium altitude, incineration does not seem necessary. However, the yields decrease rapidly 18 months after clearing. Trials have shown positive results with the use of manure.
In regions of low altitude, the depth of peat is between 70 and 80 cm; the loss after calcination, 50 to 65 percent. Trials carried out in the Luguma Swamp have clearly demonstrated that skillful regulation of the water level, thorough incineration of all aerial vegetation and rhizomes and good cultural practices, can make these organic soils productive.
The histosoils (or organic and peat soils) of the volcanic zones are more fertile.
When peaty soils have to be reclaimed for fish farming, the drainage has to be done slowly and progressively in order to avoid irreversible and undesirable changes in the structure and water relations. The water table may not be lowered more than 0.80 to 1.00 m below ground surface.
When fibrous peat occurs, the incineration of the superficial layers is recommended before or during drainage. These fibrous materials will be transformed into ash, and when mixed with the other layers the acidity will be slightly reduced.
1 Mineralisation: the change from the organic state to the mineral state is, for example, the case in the nitrogen cycle, when nitrogenous organic material is transformed into ammonia
The correction of excessive acidity by liming facilitates the humification of the organic matter and nitrification. Nitrogen deficiency can be corrected by application of fertilizers. This, combined with liming, is the best way to ensure fertility, but due to the high costs of fertilizers in Rwanda, it is not certain that such treatment would be financially viable.
When contemplating fish farming, it is necessary to carry out a complete soil survey, including soil and water analysis, to establish the need for liming and fertilization of the ponds.
See also Annex 9.
The following combinations are recommended for trial:
i. Tilapia nilotica (phytoplankton feeders): 2 fingerlings/m2 (200 fingerlings/are) + 1 fingerling/m2 (100/are) of T. rendalli (herbivore) + 1 fingerling/m2 (100/are) of T. macrochir (plankton eater and browser);
or ii. T. nilotica: 200 fingerlings/are + Clarias lazera or C. mossambica = 100 fingerlings/are;
or iii. T. nilotica: 200 fingerlings/are + T. rendalli = 100 fingerlings/are
To all these combinations, one should add about 10 Haplochromis mellandi or Astatoreochromis alluaudi fingerlings/are to control snail populations.
Pigs are reared in pens built over the ponds on piles at a density of 100 pigs/ha (1 pig/are). Normally one sow produces three broods of 6 to 8 piglets each in two years. Thus, one can sell an average of 8 to 10 pigs/year/sow in reproduction. The piglets are weaned at two months (weight between 12 and 15 kg) and are ready for fattening. Castration has to be done at one month. With proper feeding the average weight of market pigs is 70 to 72 kg after six months and 85 kg at seven months.
In ponds stocked with Tilapia nilotica at a rate of 2 fingerlings/m2, the average production of fish can reach between 8 000 and 10 000 kg/ha/year and 6 000 to 9 000 kg of pigs (on the hoof) per ha/year (Vincke, 1976).
Ducks are reared in pens over the ponds at a density of 1 000 to 1 500 ducklings/ha (10 to 15/are). Peking and Moscovy ducks are generally raised in Africa. The shelter, where ducks are fed and spend the night, is built over the pond on poles. The floor is made of lattice work to permit droppings and feed wastes to fall into the water. Under good conditions ducks reach 2 kg after 8 to 9 weeks.
Ponds are stocked with fish at the usual rate of 2 to 3 fingerlings/m2 and production can reach 2 500 to 4 500 kg fish/ha/year and 1 500 kg of duck per ha/year.
For large-scale fish-cum-duck culture, a well-operated breeding and duckling distribution centre is needed. The production of ducklings is, of course, dependent upon the maintenance of an adequate brood stock (1 male to 4–6 females) of a selected strain. During one laying season and under good conditions a Peking duck will lay 120 to 160 eggs. During peak production, two eggs are laid every three days. One female duck will produce 70 to 80 one-day-old ducklings during a laying period of eight months under suitable conditions (Woynarovich, 1979).
The list of species that seems suitable for culture in Rwanda includes the following: Tilapia nilotica, T. rendalli (or T. melanopleura), T. macrochir, Clarias lazera, C. mossambica, Haplochromis mellandi, Astatoreochromis alluaudi and, eventually, common carp, grass carp and silver carp. The breeding stations should therefore be equipped to make available fingerlings of some or all of these species.
Small ponds (100 to 400 m2) which can be drained quickly and easily are most suitable.
(a) Tilapia nilotica
Fingerling production of T. nilotica (natural spawning in ponds) is relatively easy and can be carried out in all breeding stations in the country. Those fish destined to become broodstock should be reared at a stocking rate of 2 fingerlings/m2. Tilapia nilotica broodfishes should be stocked in spawning ponds of 1 to 4 ares (= 100 to 400 m2 at a density of 14 females and 6 males/are, or 20 broodfishes per 100 m2. Average individual weight of females will be around 150 g and for the males between 150 and 200 g.
Under Rwandan conditions each T. nilotica female might be expected to spawn about five times a year with an average of perhaps 400 fry per spawning. Each female would thus produce perhaps 2 000 fry/year. Assuming a mortality rate of 10 percent during a two-month rearing period, fingerling production of one female might be 1 800 one-month-old fingerlings per female and per year.
Spawning ponds should be fertilized using manure (3 to 5 kg/are every two weeks) or well decomposed compost (20 to 30 kg/are/month).
When harvesting the fingerlings, the spawning ponds should be drained the first time after three months and every one or two months afterwards, except in the cold season.
The small fingerlings should be stocked in fertilized growing ponds until big enough to be transferred to production ponds (8 to 10 g). The following fertilization can be applied:
manure: 5 kg/are every two weeks, or
compost: 20 to 30 kg/are/month
If inorganic (chemical) fertilizers are available at competitive prices, one could apply the following monthly: superphosphate: 0.400 kg/are + ammonia sulphate: 0.200 to 0.400 kg/are or urea: 0.100 to 0.200 kg/are + agricultural lime: 1 kg/are.
Stocking densities in growing ponds should be 500 fingerlings/are (or 5 fingerlings/m2). Fingerlings will stay about two months in the growing ponds and should be fed daily. Some diets are described in Annex 8 of this report.
(b) Tilapia macrochir and T. rendalli (T. melanopleura)
Reproduction of these two species has to be done in the same way as for T. nilotica.
Tilapia macrochir is likely to spawn 4 to 5 times a year with an average of perhaps 500 fry per spawn. Tilapia rendalli is more prolific than the microphagous and planctonophagous T. macrochir and T. nilotica and may spawn 5 to 7 times a year with an average of perhaps 2 000 fingerlings/spawn.
(c) Clarias lazera and C. mossambica
If the various species of Clarias do not spawn naturally in ponds, induced spawning should be tried using hypophysis and desoxycorticosterone acetate.
(d) Haplochromis mellandi and Astatoreochromis alluaudi
For reproduction, these species have to be kept in separate spawning ponds to avoid cannibalism. Stocking rates should be around 20 adults (10 males and 10 females) per are.
The deliberate feeding of fish benefits growth by supplementing the natural food present in the ponds. The feasibility of supplementary fish feeding in Rwanda depends, however, on the availability of cheap foodstuffs and agricultural by-products with a sufficiently high food conversion rate (CR).
Many of the wastes and by-products potentially suitable as feed are grown and processed in the vicinity of towns such as Gisenyi, Ruhengeri, Kigali and Butare, far away from most villages.
Diets for fish might be prepared using locally available feed stuffs which can be surface broadcast. Fish farms might, however, have to be equipped with grinders to allow the grinding of feed stuffs such as maize, cotton seed, etc., for preparing diets for fish.
Availability and use of wastes and by-products
The following agro-industrial by-products are available: draff (brewery waste), brewery yeast, draff from banana beer and sorghum beer, slaughter waste (blood, stomach contents and bones), rice bran and rice polishings, wheat bran and regrindings, sugar cane waste and molasses, household scraps, cassava waste, soybean cake, maize (grains, meal and bran) and coffee pulp.
Draff (beer waste): is produced as a by-product in the brewery industry at Gisenyi. The present production is 1 400 t/year approximately, and draff can be obtained free of charge. A new brewery will be established soon at Kigali. The conversion rate of draff, properly used, is 12:1 (12 kg draff is needed to obtain 1 kg fish). Up to 20 percent of draff can be used in fish feed, and up to 15 percent can be fed to pigs and ducks if associated animal husbandries and fish farming is envisaged. Tilapia nilotica stocked at a rate of 2 fingerlings/m2 and fed only with wet draff supplied bi-weekly at a rate of two-thirds of estimated weight of fish population in the pond have been known to yield as much as 3 500 to 4 000 kg fish/ha/year.
Brewer's yeast: is an excellent source of protein of high nutritive value and digestibility. In poultry and pig rations it is generally included at levels of 2 to 5 percent (Göhl, 1975). Usually available as slurry, it has to be dried or cooked to de-activate the yeast cells. The brewery at Gisenyi produces 200 000 litres approximately of yeast (slurry) per annum, available free of charge. The total production is at present discharged into Lake Kivu.
Draff from banana beer: according to Morris (1979), the total banana production of Rwanda was 1 896 253 tons in 1978, at an average price of Rw.F. 700/kg. Between 36 and 100 percent (average 76.9 percent) of the banana production is utilized for the preparation of banana beer (the average consumption of banana beer is 281 kg/person/year (Morris, 1979)). One needs 2.5 to 3 kg of bananas to obtain 1 litre of beer. Banana beer is prepared in almost all villages, all the year round. About 987 000 000 tons of banana draff is available annually in the country, with a CR of 10:1 (10 kg of draff needed to produce 1 kg of fish). A 200 litre petrol drum, containing about 180 kg draff of locally made beer (banana or sorghum beer) can be bought in Butare for Rw.F. 300, and in Kigembe for Rw.F. 400 (between Rw.F. 1.67 and 2.22/kg draff).
Draff from sorghum beer: the sorghum production reached 163 776 tons in 1977 (Morris, 1979). When preparing beer 84.7 percent of the harvest is used (1 kg sorghum = 2 litres beer). The annual production of sorghum beer draff is about 20 800 tons, with a CR of 10:1. Draff of sorghum beer is available all the year round in almost all villages at little or no charge.
Slaughterhouse wastes: sheep, goats and cattle are presently sold in 60 traditional markets. They are slaughtered in three abattoirs (Kigali, Butare and Rusumo), 28 slaughter houses and 276 slaughter places (Morris, 1979). The waste is most often discharged into rivers. Slaughterhouse wastes include entire carcases of animals that have died from diseases; carcases or parts of carcases that do not pass inspection; fresh blood; inedible parts of the digestive tract; reproductive organs and bones and other trimmings not regarded as edible. Normally, in Rwanda, only blood, stomach contents and bones are available.
It is possible to utilize offal to feed fish, pigs and poultry. In diets based on cereal grains and other plant products, it is difficult to avoid a deficiency in essential amino acids and in some vitamins, and slaughterhouse waste can supply these amino acids and vitamins. Even when used in small amounts they vastly improve the nutritive value of the entire fish feed diet (Göhl, 1975).
Blood meal: contains only small amounts of minerals but is very rich in protein. However, it is of a rather inferior amino acid composition. The digestibility of raw blood is very high.
Approximately 390 000 kg of raw blood is available annually in Rwanda. This quantity, if recovered, could be used as food for fish, pigs and poultry. Blood meal can easily be produced on a semi-commercial scale. The blood is collected at the abattoir and boiled very slowly in a large pot over an open fire until coagulated and the water evaporated. Continuous stirring is necessary. When coagulated, the blood is then spread onto a concrete floor or galvanized sheets, dried in the sun and then cooled off and dried completely in a well-ventilated shed. When completely dry, the blood meal is scraped off with a shovel and milled to obtain a black meal. According to Göhl (1975), 1 000 kg of liveweight carcass yields about 6 kg of blood meal.
Another way to utilize blood is to absorb it in wheat middlings, rice bran or citrus meal and then spread it out on trays heated from below or dried in the sun. The process may be repeated several times. In this way, the low protein vegetable matter is enriched with protein.
Blood can also be coagulated by the addition of 1 percent of unslaked or 3 percent of slaked lime and the coagulate then dried. Many minerals and 10 to 15 percent of the dry matter are lost if the coagulate is used rather than the whole blood for production of blood meal. Blood meal made from whole blood will contain more isoleucine, one of the essential amino acids (Göhl, 1975).
Raw blood can be preserved by the addition of 0.7 percent formic acid or sulphuric acid. Blood treated in this way may be stored for about one week. If 0.5 percent potassium metabisulphite is added to sulphuric acid treated blood, it may be kept for a few months before feeding (Göhl, 1975).
Fresh blood can be used to feed fish (weekly application of 5 to 10 litres/are), but it is generally mixed with stomach contents or with bran.
Feeding trials carried out by FAO in the Central African Republic have shown the usefulness of locally produced blood meal in diets for Tilapia nilotica and Clarias lazera. Using a ration composed of 15 percent draff, 20 percent wheat bran, 15 percent rice bran, 30 percent cotton seed cake, 7.75 percent sesame cake, 5 percent fish meal, 5 percent blood meal, 2 percent bone meal and 0.25 percent vitamin mix, with T. nilotica at a stocking density of 20 000 fingerlings/ha, the net production was 6 180 kg/ha/year, with a CR of 1.63 (Miller, 1976). Protein content of the feed was 35.72 percent. A wet combination of cow stomach contents, coarse-ground cotton seed meal and fresh blood in a proportion of 2:1.5:1, yielded a mean net production of 4 309 kg/ha/year with T. nilotica stocked at 20 000 fingerlings/ha. The costs per kg were CFA.F. 37.6 (= U.S.$ 0.16/kg) and a mean feed conversion of 9.4 was achieved in ponds ranging from 31 to 48 ares in area (Miller, 1976).
Stomach contents: undigested feeds present in the rumen of cattle at slaughter amount to about 20 to 22 kg for a 240 kg animal starved normally before slaughter and presents a large disposal problem for abattoirs. This material is usually washed into rivers or piled and allowed to decompose. Rumen content contains not only the vitamins present in the feed ingested before slaughter, but is enriched with B vitamins from the rumen flora (Göhl, 1975). The composition of fresh rumen contents is as follows: carbohydrates, 36.2 percent; fats, 1.0 percent; total protein, 11.6 percent; and fibre, 37.8 percent (Miller, 1976).
Several hundred tons of stomach contents are available annually in Rwanda and this material, not yet utilized, can be collected and used as feed for fish, at almost next to nothing for the farmer. Transport costs however, are Rw.F. 45/ton/km. Stomach contents can also be used to prepare compost, mixed with grasses and farm wastes.
The rumen contents can be preserved by the addition of sulphuric acid to reach a pH of 3.0, by ensiling together with molasses, or by drying, either in the sun or on trays heated from underneath. If used for feeding, it is important the material is dried immediately. Rumen content silage is palatable to pigs and they can consume up to 0.5 kg per day when they have become accustomed to it. It has also been used mixed with blood in poultry diets (Göhl, 1975).
In fish farming, stomach contents can be mixed with rice bran, wheat bran, draff, blood, etc.
Bone meal: is used as a source of phosphorous and calcium in fish diets. It also provides trace elements. There are different types of bone meal, according to the processing: green bone meal, steamed bone meal, raw bone meal, calcined bone meal, etc. With simple equipment, bones can be processed either into raw bone meal or calcined bone meal; steamed bone meal requires more expensive equipment.
Calcined bone meal or bone ash is the only recommendable method of utilizing bones. It is made by piling the bones on a metal frame and burning them. Burning sterilizes the bones and deprives them of all organic matter. The charcoal-like bone ash is friable and can easily be pulverized (Göhl, 1975).
Calcined bone meal is rich in calcium (34 percent Ca of dry matter) and phosphorous (16 percent P of dry matter). (Göhl, 1975.). Bone meal is added up to 5 percent in diets for fish. Bones are in plentiful supply in Rwanda, in the abattoirs and slaughterhouses, generally free of charge.
By-products of rice-milling: threshed rice or paddy, or rough rice, has to be processed to free the paddy from the hull, germ and bran. In many countries this process is carried out in a one-stage mill. The by-product from these mills is a mixture of hulls and bran. In Rwanda, rice bran and rice polishings are available.
Rice bran: represents between 2 and 4 percent of the weight of paddy. In 1975, 2 480 tons of paddy were produced in Rwanda, giving about 70 tons of rice bran. Irrigated rice is produced in Rwanda in Kabuyé (10 km from Kigali) and in the prefectures Cyangugu, Butare and Gitarama. Rice is harvested in August/September and February/March. Husking is done in Butare and Kigali in September and March. Rice bran yields a CR of 4.5 and up to 20 percent can be used in fish feeds at a cost of Rw.F. 2 000/ton. For pigs, rice bran should not exceed 30 to 40 percent of the total ration to avoid soft pork. Up to 25 percent can be included in rations for poultry and double that amount has successfully been used in experiments (Göhl, 1975).
Rice polishings (‘farine basse’): represent about 6 percent of the paddy weight. About 150 tons of rice polishings were available in Rwanda in 1975, at a cost of Rw.F. 2 000/ton. The CR of rice polishings is between 3 and 3.5 and up to 35 percent can be used in fish feeds.
By-products of wheat milling: the wheat grain (or endosperm) is covered with two kinds of fibrous coatings: the coarsest outer one is called bran and under this one a less fibrous aleurone layer (albumen of cereals). During milling the starchy endosperm is separate from the other part of the grain.
Whole wheat after milling yields between 70 and 80 percent white flour and 20 to 30 percent offal consisting of coarse bran, fine bran (aleurone) and germ. The waste consists generally of 2.5 percent of coarse bran, 40 percent of fine bran and 57.5 percent remillings or regrindings (‘remoulages’).
In the Ruhengeri area 2 300 tons of wheat were produced in 1975, leaving about 460 tons of sharps (‘issues de blé’), of which 190 tons were bran and 260 tons, remillings.
Wheat bran: is excellent for fish as well as for pigs and poultry. There is no sharp difference between fine bran and coarse bran and these two by-products are generally mixed. The bran fractions contain most of the vitamins and protein of the wheat grain. The protein content of bran is between 14.5 (Hastings, 1973), and 16.9 percent (Göhl, 1975). Up to 35 percent of wheat bran can be used in fish diets, up to 30 percent in pig diets and up to 15 percent in poultry diets. Wheat bran costs Rw.F. 2 000/ton in Ruhengeri.
Remillings: are the most common by-product from the flour mills, and up to 45 percent can be used for fattening pigs. Up to 10 percent can be used for poultry and up to 20 percent can be utilized in fish feeds. Remillings contain between 15 and 19 percent protein. The cost per ton in Ruhengeri is Rw.F. 2 000 to 2 500.
Sugar-cane wastes: about 14 000 t sugar-cane was produced in 1975 in the Kabuye area. The by-products of the sugar-cane industry are bagasse, molasses and filter presscake.
Bagasse: is the cane waste after it has passed through the crusher where sugar sap is extracted. It represents about 15 percent of the whole sugar-cane plant. An average of 60 percent of the bagasse produced is generally used as fuel in the sugar mills.
There are two kinds of bagasse fibres: (i) fine, strong and flexible fibres that are suitable for the manufacture of high-grade pulp and paper, and (ii) short fibres or pithy material (bagasse pulp), which are used as animal feed.
The bagasse production in Rwanda is about 2 100 tons/year. Bagasse or portions of bagasse can be used as roughage for pigs and cattle, or as a carrier for molasses. Bagasse and bagasse pith are good carriers of molasses (four parts bagasse pith and ten parts molasses cane). Bagasse can also be used for compost.
Molasses: is a liquid by-product (80 percent dry matter) containing sugar and nonprotein nitrogen; about 2.5 percent of the whole sugar-cane plant. About 350 tons of molasses are presently available in Rwanda. There are different ways in which molasses can be utilized (Göhl, 1975):
In dry feeds: molasses have to be absorbed to simplify their transport and handling. Used as a binding product, molasses can replace other more expensive carbohydrates in feeds. Percentages of molasses absorbed by some feed ingredients are as follows: wheat middlings, 19 percent; maize meal, 15 percent; draff, 9 percent. Up to 15 percent of molasses can be fed to pigs and to poultry, and 10 to 15 percent can be included in fish diets. The maximum amount of molasses used is often determined by the absorbability of molasses by the other ingredients in the diet.
Trials undertaken in the Ivory Coast, with 30 g fingerlings of Tilapia nilotica (stocking density: 1.3/m2), feeding a mixture of 60 percent molasses and 40 percent rice bran have given the following results: yield: 3 649 kg fish/ha/year; average daily growth increment: 0.78 g/fish/day; CR = 8 (Lazard, 1980).
In silage making: molasses are quickly fermented and, at a 5 percent level, sometimes added to grass during the ensiling process to preserve the nutrient value and increase palatability.
Filter press cake (‘tourteaux de filtration’): represents about 2.5 percent of the whole of the sugar-cane (as it stands before harvesting). This product is obtained when the chopped cane is pressed and the sugar is extracted with water. Filter press cake contains many of the impurities of the sugar-cane juice and in organic compounds, mainly calcium sulphate and calcium phosphate. The protein content is between 10 and 15 percent (Göhl, 1975).
Filter press cake is generally used as a fertilizer for sugar-cane cultivation but it can also be used as a fertilizer in ponds, and to feed fish when mixed with bran or draff.
Maize and by-products: In 1977, 77 166 tons of maize was produced in Rwanda (Morris, 1979).
Maize (grain): is a staple food for the population and its possible use as a fish feed is questionable from the socio-economic point of view. The majority of the maize milling capacity is concentrated in centres and the cost of transport to remote areas is high. If used, and to avoid prohibitive costs, maize should be milled at the fish farms using a commercial hammer-mill. Maize (grains) costs Rw.F. 10 000/ton.
Maize meal: is available in almost all the prefectures and costs about Rw.F. 17 000/ton. Maize meal levels of 15 to 30 percent are used in fish feeds and 15 to 70 percent in pig and duck feeds. In fish culture the CR of maize meal is between 3.5 to 3.9 percent.
Maize bran: is available in some villages, but in small quantities. The optimum level in pig rations is between 20 to 25 percent and about 30 percent in fish diets. Maize bran costs Rw.F. 2 000/ton and the CR is between 4.5 and 5.5 percent.
Groundnuts: between 12 and 14 000 tons (in hulls) were produced in 1975, mainly in the Cyangugu, Kibuye, Gisenyi, Gitarama and Kigali prefectures, as well as in the eastern plateau and eastern savanna. According to Morris (1979), some peanuts, perhaps 50 percent of the supply, are available for oil extraction.
Groundnut press-cake is available in only very small quantities and prices fluctuate from year to year. Shelled weight of peanuts is 70 percent of the weight in the shell. Oil is 50 percent of the shelled weight and the other 50 percent is press-cake (Morris, 1979). The groundnut press-cake content may be 30 to 45 percent in fish feed, 23 to 27 percent in pig feed and 5 to 7 percent in duck feed. Groundnut press-cake contains 53.5 percent protein.
Soybean: the production for 1975 was 2 700 tons, mainly produced for human consumption in the Kibuye (Gitesi), Cyangugu (Bugarema) and Kibungo (Kayonza) prefectures. Soya is mainly grown between 1 400 and 1 800 m altitude.
Soybeans are the richest by far in protein of all the common seeds used in feeds. Soya seeds have a low oil content (maximum 20 percent). Beans are 72 percent of the pod weight. When pressed the oil cake represents about 80 to 82 percent of the seeds and 18 to 20 percent is oil.
Locally-produced soybeans sell at Rw.F. 25 000/ton and imported soya is processed in Kigali. In 1975, 15 300 tons of soybeans were pressed, producing about 10 000 tons of soya oil-cake.
Coffee by-products: the coffee production (‘café marchand’) in Rwanda was 24 385 tons in 1975. The by-products of coffee are pulp and coffee hulls.
Coffee pulp: represents about 26 percent of the whole coffee fruit (‘cherry’ or ‘cerise de café’). The coffee fruit can be processed either by the simple dry method or by the more advanced wet method to liberate the seeds (‘coffee beans’) from the fleshy wet pulp. Large quantities of coffee pulp (about 10 000 tons/year) are available in Rwanda, free of charge. Coffee pulp can be used as a roughage for cattle and for pigs and also as fish feed, after drying. Wet pulp should be dried immediately (in the sun, as described for brewer's yeast), as it spoils very quickly. Coffee pulp contains between 7 and 9 percent protein (Mongodin, 1977).
Up to 16 percent dehydrated coffee pulp can be included in pig rations (Göhl, 1975), and up to 25 percent in fish diets.
Coffee hulls (‘parches de café’): are obtained during the decortication process of the coffee beans, and represent 15 percent of the ‘café parche’. About 3 000 tons of coffee hulls are available in Rwanda, free of charge. The protein content of coffee hulls is between 6 and 12 percent. Coffee hulls have to be mixed in diets and can be used up to 20 percent. If used as a single feed, CR of coffee hulls is 40 (Lazard, 1980).
Cassava waste: In 1977, 414 326 tons of cassava were produced in Rwanda, at a value (market price) of Rw.F. 8 000/ton. The average consumption of manioc (Cyangugu Prefecture) is about 113.2 kg/per caput/year (Morris, 1979).
Cassava tubers or roots have a poor protein content (about 3.6 percent), but protein content in the peel and in the external parts of the root is relatively high. By retting cassava, a necessary practice to liberate the hydrocyanic acid from the tubers, some of the nutrients are dissolved in the water.
Peeled cassava (‘manioc pelé’), after retting, represents about 68 percent of the fresh tubers. Offals are about 32 percent of the fresh roots. ‘Cossettes’ are 33 percent and flour, 31 percent of the fresh root weight (Morris, 1979).
Hydrocyanic acid can cause fish mortality if too much cassava is retted in a small water area. According to FAO trials set up in the Central African Republic (CTFT, 1972), the fish mortality (Tilapia nilotica) is as follows:
peelings of 10 kg raw cassava tubers in 100 litres of water: total fish mortality occurs after 24 hours (density not stated);
peelings of 5 kg raw cassava tubers in 100 litres of water: high mortality occurs after 48 hours;
peelings of 1 and 2 kg raw cassava tubers in 100 litres of water: no mortality occurs.
Trials on cassava retting in fish ponds were undertaken in Gabon with the following results (CTFT, 1972):
|10 kg raw cassava tubers per are/week||2 400 kg fish per ha/year|
|100 kg " "||4 280 " "|
|200 kg " "||4 000 " "|
One should note that retting large quantities of cassava tubers to obtain only a few kilogrammes of fish can still be economical. Since retting bitter cassava is absolutely necessary before consumption, it is generally done in brooks and rivers instead of ponds.
As cassava is a staple food in almost the whole country, retting cassava tubers is carried out in many villages. It can also be carried out in fish ponds, using approximately 100 kg tubers per are/week. With this method, the average yield can reach between 3 000 and 4 000 kg fish per ha/year.
Household scraps: are very nutritious, but are not always collected and utilized as fish feeds. Pot scrapings, vegetable wastes and fruits (Mango, papaya, etc.), cassava offal, rice, maize, etc., are available daily in all families and can be collected as fish feed. Depending upon the composition of the scraps, CR is between 8 and 20.
Wastes from markets, restaurants, hospital and boarding-schools: are now used as fish feed at the Kigembe fish farm. They are collected, free of charge, mostly in Butare, and transported (19 km) to the station.
The cost of these ingredients delivered at Kigembe is about Rw.F. 0.85/kg. The CR of these wastes is between 6 and 25 (6 to 25 kg wastes, depending on their nature and average composition, needed to produce 1 kg fish).
Wastes from markets, because of their nature (leaves, stalks, bunches of bananas, spoiled fruits, sweepings, etc.), are sometimes better for composting than for direct feeding in ponds.
A. Diets with 25% Protein (kg)
|Ingredients||Percentage Compositions of Various Compounded Feeds|
|Brewery waste, dry||-||28||-||-||-||9||-||-||-||-||9||-||20||-|
|Brewery waste, wet||-||-||80||-||-||-||37||-||-||-||-||36||-||81|
|Brewery waste, dry||-||28||-||-||-||9||-||-||-||-||9||-||20||-|
|Brewery waste, wet||-||-||80||-||-||-||37||-||-||-||-||36||-||81|
1 It is doubtful whether the use of ‘premix’, a prefabricated mixture of vitamins, is feasible for rural fish farmers. Its use should, therefore, be considered optional.
Source: K.W. Chow (pers.comm., 1980)
When using chemical (inorganic) fertilizers, such as superphosphate, triple superphosphate, ammonium and urea, it is recommended to apply these fertilizers every two weeks (Miller, 1976).
While awaiting the results of new trials to be undertaken at the Kigembe Centre, the following rates of application of inorganic fertilizers are recommended:
Superphosphate (18% p2O5): 0.300–0.400 kg/are, fortnightly
Triple superphosphate (45% P2O5): 0.150 kg/are, fortnightly
Ammonium sulphate (20% N): 0.200–0.300 kg/are, fortnightly
Urea (46% N): 0.100–0.200 kg/are, fortnightly
Using only superphosphate and ammonium sulphate at the above rates, the cost of fertilization, including application, will be about Rw.F. 980 per are/year or Rw.F. 98 000 per ha/year.
Liming is indispensable when the pH of the water is too low (below 6.0–6.5). The best water for fish cultivation is that with a pH between 7.0 and 8.0. As already explained, marshy and peaty water are too acid.
The nitrification of ammonium compounds into nitrites and nitrates demands the presence of sufficient quantities of lime.
The principal fertilizers containing lime useful for liming ponds are: powdered limestone, marl, quicklime, caustic lime and calcium cyanamide. At present, only powdered limestone is available at Rubona and costs Rw.F. 16/kg.
For the purpose of controlling the acidity of the water, one can use powdered limestone at the following rates of application:
in new ponds with acid water (pH between 4.0 and 6.5): 15–20 kg/are (1 500–2 000 kg/ha) on the bottom when the pond is dry. After spreading out, powdered limestone has to be lightly worked in and the pond can be filled. The cost of such an application is estimated to be Rw.F. 240–300 per application and per are.
other ponds: monthly application of 1.5 to 2 kg/are, at a cost of Rw.F. 288–384 per are/year (Rw.F. 28 800–38 400 per ha/year).
Relatively high production can be obtained combining organic fertilization of the ponds and supplying supplemental feed. The following is a brief summary of the availability and application of various manures:
Cow manure: is relatively easy to obtain in the country. One cow produces annually about 16 tons of manure, which can be used to fertilize a 1-ha pond at a rate of 300 kg manure/ha/week (or 3 kg/are/week).
Horse manure: may also be used, but is often not available in large quantities. Recommended application rate: 20 to 30 kg/are, monthly.
Pig manure: raising of pigs in pens and beside or over fish ponds, permits continual organic fertilization of the ponds and appears to work very well with Tilapia nilotica as well as other tilapia species, and common carp.
Poultry manure: in Central East Africa, Maar et al., (1966) recommended the use of poultry manures at a weekly application rate of 120–220 kg/ha (6 240–11 440 kg/ha/year). The manure produced in a year by 100 chickens is about 1 900 kg. In tilapia culture (T. nilotica, two fingerlings/m2) with artificial feeding, the application of poultry manure at an initial rate of 2 500 kg/ha, followed by monthly applications of 1 000 kg/ha (12 000 kg/ha/year) gives an additional production of about 1.5 tons tilapia/ha/year. This manure can only be used if there are poultry farms near the ponds.
The composition of some manures is presented in Table A.
Composition of Various Manures
|N (%)||P2O5 (%)||K2O (%)||CaO (%)|
When manures are not steadily available one can utilize compost for the fertilization of the ponds, as is practised in rural ponds in the Central African Republic. Natural productivity in ponds in Central Africa is around 200 kg fish per ha/year. In monoculture of T. nilotica stocked with 2 fingerlings/m2, the average production from ponds where compost is used is 1 500 kg fish/ha/year. The compost is stacked underwater in a 1 m3 pile in the corner of the filled pond, with weekly doses of 9–10 kg organic matter (grasses, spoiled fruits, wastes from soaking cassava and some cattle or chicken manure) then being added to the pile. To collect, transport and pile the organic matter for composting a 100 m2 pond, the farmer may spend an average of 28 hours a year.
With aerobic prepared compost, production can reach 3 000 kg of fish/ha/year, with an application rate of 20–30 tons compost per ha/year (C.T.F.T., 1972).
The fertility of compost depends broadly on the mineral content of the used grasses and organic matters to prepare the compost, and the method of preparation (aerobic or anaerobic methods). Organic matters, stacked underwater in piles scattered around the edges of filled ponds, generally produce relatively low fertility, because decomposition is anaerobic and slow. Decomposition (rotting) of organic matters in compost piles (aerobic conditions) is more rapid and more complete, giving a richer fertilizer than the anaerobic prepared compost.
Preparation of compost under aerobic conditions is easy. A trench of about 1.20 m wide and 0.50 m deep is dug. The length of the trench depends on the quantity of compost needed. To obtain good fermentation, it is necessary to apply alternatively a layer of fresh fodder, rich in nitrogen and then a layer of dried organic matter. Fresh fodder can be composed of all kinds of organic wastes (spoiled fruits, vegetable wastes, garbage, household refuse, sweepings, etc.), but no woody material. The dried organic matter is made from grass and is arranged in piles of 20–30 cm thick layers in the trench to a height of 1.50 m. The layers should be compressed slightly and, if available, some manure or ash (rich in minerals) can be added between the layers. Coarse materials should be chopped before piling.
Between 5 and 7 tons of organic matter is needed to prepare a 9 m3 compost pile. One of the best composts is prepared with a mixture of green fodder and household refuse, garbage from towns and night soil. When the pile is made up, water has to be sprayed on it to initiate the fermentation process (about 30 litres water/day is needed for a 9 m3 pile, except during the rainy season). Approximately one month after completing the pile it is necessary to mix and turn over the compost and then place it in another trench. Only during the dry season should watering be continued. Decomposition is complete about two months after the turning over of the pile. Thus, compost can be prepared every three months, giving each time about 2 800 kg compost for a 9 m3 pile. The cost of preparing such compost is estimated at Rw.F. 400/ton. At doses of 20–30 tons/ha/year, composting of ponds costs between Rw.F. 8 000 and 12 000/ha/year.
The best fodders are made from leguminous plants rich in protein and minerals, such as aerial portions of peanut (Arachis hypogaea), Calapogonium muconoïdes, Crotolaria mucronata, Dolichos lablab, Soya, Leucaena glauca, Pueraria thunbergiana (Kudzu), Mucuna utilis (Velvet bean), Stylosantes sp., Vicia sativa and Voandzeia subterranea.
Grass has to be cut from natural (or artificial) grasslands around the fish farm if the cuttings from grasses on the dikes of the ponds are not sufficient to make up the compost piles. Common grasses, such as Brachiaria ruziziensis, Chloris gayana, Cynodon dactylon, Hypparrhenia rufa, Imperata cylindrica, Loudetia arundinacea, Paspalum spp., Pennisetum glaucum and P. purpuream are very suitable for making compost. Also, aquatic grasses growing along rivers, in swamps and in ponds are suitable, such as Echinochloa pyramidalis, E. staginina and Leersia hexandra, containing between 5.8 and 11 percent crude protein (CP) and between 8.6 and 16 percent ash (Göhl, 1975).
If only grasses and a few organic matters are available, artificial manure can be used to fertilize the ponds. The preparation of artificial manure is roughly the same as that for compost, but chemical nitrogen fertilizer (generally urea) is added to the grasses and organic matter during the preparation of the manure. Artificial manure of good quality is as rich as farmyard manure and one ton contains approximately 150–180 kg organic matter, 4.5–5.4 kg nitrogen, 2.0–2.5 kg phosphoric acid, 6–7 kg potassium and 4–5 kg of calcium, depending on the mineral content of the grasses and organic matter used to prepare the artificial manure, the fertilizers used and the methods of preparation.
The following method of preparation of artificial manure was suggested during 1972–73 at the Agriculture Section of the Institut Technique Agricole du Burundi (ITAB) (De Valck, pers.comm., 1978):
In a trench of 4 × 4 m and 1.75 m deep (28 m3) fresh chopped fodder is placed in 20–30 cm thick, not compressed, layers. Between each layer urea should be sprayed (46 percent N). To fill the 28 m3 trench, about 17 tons of green organic matter is needed, together with 8 kg of urea. The pit, after filling, has to be covered by earth and water and sprayed (about 60–70 litres/day), except during the rainy season. After one month the trench has to be emptied for aeration of the manure. The manure has to be turned over and replaced in the same pit for one more month. Generally after two months, 9 tons of manure is ready for use. Application rate of artificial manure in ponds is between 20 and 30 tons/ha/year at a cost of Rw.F. 7 500–11 300/ha/year.