Mineral status of African catfish (Clarias gariepinus) fed diets containing graded levels of soybean or cottonseed meals

In order to assess the effect of increasing levels of dietary soybean meal (SBM) or cottonseed meal (CSM) on growth and body mineral composition of juvenile African catfish, five isonitrogenous (39% crude protein) and isocaloric (13 kJ g, digestible energy) diets containing various levels of soybean meal (SBM30 and SBM60) or cottonseed meal (CSM30 and CSM60) as partial replacement of fish meal (Control) were fed to triplicate groups of 50 fish (initial mean weight: 10.3 g) in each tank (0.9 m). Over an 8-week feeding period, significant differences (P <0.05) were observed on growth, body nutrient and mineral composition between fish fed the experimental diets. Fish fed 600 g kg SBM- or CSM-based diets had reduced growth compared to those fed a diet containing 300 g kg CSM or the control diet. Survival, feed utilization and hepatosomatic index were not significantly affected by the inclusion level of SBM or CSM in the diets. Fat content was higher in carcass and fillet of fish fed CSM-based diets than those fed SBM- or fish meal-based diets. Body mineral composition in response to dietary treatment revealed a reduction in carcass Ca and P content with the increasing levels of SBM and CSM in the diets while Mg, K, Fe, Zn and Mn content in carcass did not show any marked change (P > 0.05). However, fish fed SBM- or CSM-based diets have reduced Zn in the fillet than those fed the control diet (P <0.05). Moreover, significant correlations were found between body mineral composition and dietary SBM, CSM or phytic acid level, respectively. This study showed that as well as growth is concerned, SBM and CSM can replace fish meal as a source of protein in compound feed for African catfish up to 300 g kg. However, in regard to body mineral composition, the inclusion level of these ingredients in the diets should be less than 300 g kg and this may be mainly because of the presence of phytic acid in the feed ingredients used.