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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
close this folderOrganic residues in aquaculture
View the document(introductory text...)
View the documentIntroduction
View the documentThe range of production in aquaculture
View the documentThe value of organic wastes
View the documentDirect feeding
View the documentConcluding remarks
View the documentReferences
View the documentDiscussion summary

Direct feeding

Feeding types among fishes range from predatory gulpers to sifters of organic materials in mud, to zooplankton feeders, and to herbivores that eat algae or even leafy plants. As already intimated, the rationale of polyculture is the selection of compatible species with different feeding patterns. In addition, because fish learn to feed on almost anything, it is relatively easy to develop pelleted food for fish culture, dietary quality considerations aside. At the same time, such catholic feeding habits permit the use of plant materials, especially cheap or nearly valueless crop residues such as bran, etc. Table 3 (22) illustrates this, as does the practice of building very wide pond margins to the fish ponds in China for cultivating grasses where leafy plant-feeding grass carp (Ctenophryngodon idella) comprise about 20 per cent of the stock in the pond (12).

TABLE 3. Proximate Composition of Feedstuffs Used in Fish Culture

  %
Carbohydrates
%
Fats
Total
protein
%
Fibre
Baobab press cake 76.7 0.8 2.2 6.8
Beer waste 46.4 7.8 22.8 18.8
Cabbage leaves 4.8 0.1 1.7 1.2
Cassava flour, dry 83.2 0.5 1.6 1.7
Cassava leaves 14.3 1.0 7.0 4.0
Cassava tubers 34.6 0.2 1.2 1.1
Cocoa hulls 57.5 0.8 8.7 23.7
Coffee hulls 33.5 7.2 12.2 39.0
Corn, cooked 79.2 4.8 8.0 1.9
Corn bran 64.4 8.6 12.2 2.8
Corn flour 71.5 3.8 9.3 1.9
Corn grain 81.3 4.6 10.3 2.3
Corn leaves and stalks, dry 46.6 1.6 5.9 30.9
Cotton seed cake 38.5 7.4 47.3 9.6
Cotton seed 29.6 18.8 22.8 24.1
Cow stomach, dried 37.6 1.9 16.7 28.2
Cow stomach, fresh 36.2 1.0 11.6 37.8
Kale 6.1 0.8 3.5 1.6
Lettuce 3.7 0.2 1.2 0.6
Millet 81.0 2.8 9.0 3.0
Mill sweepings 58.0 14.0 12.5 7.5
Napier grass 1.0 0.2 2.6 1.1
Palm nut press cake 53.0 8.9 19.9 14.0
Peanut press cake 27.3 7.6 53.5 6.2
Peanut shells, ground 46.3 1.0 4.0 46.7
Plantain banana, whole 79.2 1.8 6.5 5.3
Potatoes 19.7 0.1 2.1 0.9
Pumpkin 4.7 0.1 1.0 0.8
Rice 77.7 2.2 7.4 0.4
Rice bran 56.9 3.8 0.7 22.6
Sorghum 81.0 2.8 9.0 3.0
Soybeans, ground 31.4 15.7 33.7 5.5
Spinach 4.5 0.2 2.1 0.8
Sugar-cane fibre 55.4 0.6 1.3 40.0
Sweet potatoes 27.5 0.2 1.6 1.0
Wheat bran 59.7 3.8 4.5 14.5
Yam 25.6 0.1 1.5 0.9
Blood, fresh 36.2 1.0 11.6 0.0
Blood meal - 1.0 76.6 0.0
Smoked, salted fish waste (local) - - 35.8 -

Source: Bardach 122).

All sorts of other wastes, even sludge, are fed to fish (23 - 25) with very low conversion efficiencies, to be sure, but presumably favouring cheap production costs just the same (Table 4).

TABLE 4. Yields of Fish for Various Residues Used in China

Residue

or

feed

Residue

or feed

quantity

Fish yield Estimated

conversion

efficiency

(kg yield/kg

feed x 100)

Grass or vegetable tops 60 - 70 kg 1 kg grass carp 1.4 - 1.7%
Snails and clams 50 kg 1 kg black carp 2.0%
"Fertile water": 77% bean curd

residue; 23%

residue of fermented products

100 kg 1 kg silver carp 1,0%
Animal manure bighead carp 25 kg 0.5 kg silver carp 2.0%

Based on information given to mission members; after Tapiador (12); conversion efficiencies are our estimates

Carnivores make up a certain portion of the polyculture components; in fact, various traditional aquaculture schemes incorporate a few voracious predators, albeit under intensively supervised management conditions, for example, pike in common carp ponds and catfish (Silurus glands) in polyculture carp ponds (1) and (A. Ruttkay, persona) communication, 1978). Sometimes pure carnivore culture is practiced depending on the availability of the so-called trash fish; that is, species that are too small to be eaten directly or not acceptable as table fare. The culture of groupers in various parts of the Pacific and of yellow tail in the Inland Sea of Japan are based on the availability of this kind of high-protein feed; it is mentioned here because one sometimes hears the argument that such practices are ecologically unsound. They may appear so at first glance, but these comments usually do not take into consideration that aquaculture is pursued to gain a livelihood, providing its practitioner with income first and foremost. It usually also supplies fish for the table, but hardly as its prime purpose. The rearing of carnivores relying on "waste" species, or for that matter on slaughterhouse wastes and/or blood meal, can be a sound practice, even from the ecological vantage point.