Short communication: Assimilation efficiency in two herbivores, Oreochromis niloticus and larvae of Imbrasia belina: a comparison

The abilities of two herbivorous animals (Oreochromis niloticus and the larva of Imbrasia belina) to digest and absorb nutrients (Assimilation efficiency) from their guts were studied. Oreochromis niloticus mainly feeds on phytoplankton and the larvae of I. belina feeds on leaves of Mophane (Colophospermum mophane) and Morula (Sclerocarya birrea) trees. The amount of organic matter in the diet of fish (100-600 mg/g D.W.) and assimilation efficiency (8-43%) were variable and an increase in the level of organic matter in the diet of fish resulted in an increase in assimilation efficiency. The organic matter in the diet of O. niloticus can only be increased when the fish ingests more algae and this improved lyses of algal cells. The organic content in the diet of the larvae was consistently high (>900 mg/g D.W.) but assimilation efficiency was not always high. The highest assimilation efficiency for the larvae was 36 ± 3.3% and the lowest was 13.2 ± 3.2%. In this study, it has been shown that the amount of organic matter in the diet and larval age are factors that could limit assimilation efficiency in fish and larvae, respectively. The proportion of cellulose material, indigestible organic matter, in the food is another constraint for both animals. As a result, both animals have only achieved about 40% maximum efficiency. Thus, more studies to understand how these and other factors affect assimilation efficiency are essential to improve production of these animals in aquaculture and larviculture. Key words/phrases: Assimilation efficiency, Imbrasia belina, lepidoptera, Oreochromis niloticus, saturniidae SINET: Ethiop. J. Sci Vol.26(1) 2003: 73-7