Aspects of protein utilization by fish

Abstract

Most animals which have been domesticated as farm animals are either omnivorous or herbivorous. By contrast most fish are carnivorous and many which are farmed, or are considered potential species for farming, have a high dietary protein require- ment. As food proteins are expensive, fish farming has tended to concentrate on esteemed species with a high market value. In general, three types of feeding regimen have been adopted, namely: (I) a pelleted ration containing a sufficiency of known nutrients; (2) trash fish (i.e. fish of little commercial value used as food); (3) a natural food chain which includes invertebrate herbivores as a component of the system. Natural food chains such as those employed in the farming of carp may proceed at different levels: (I) non-intensive with low stocking density, fertilization of the water with compounds containing nitrogen or phosphorus to stimulate a food chain, and no supplemental feeding ; (2) semi-intensive with medium stocking density, supple- mental feeding with maize, wheat or barley, and water fertilization only if the excretory products of the fish are inadequate to support a food chain; (3) intensive with high stocking density, feeding of a pelleted ration of relatively high protein content and no fertilization of pond water. At all levels of intensity, polyculture techniques (stocking together of fish utilizing different types of natural food) give superior results. Thus, for instance, carp, tilapia and mullet might be grown together.