EVALUATION OF PROCESSED OILSEED MEALS IN THE DIET OF NILE TILAPIA Oreochromis niloticus

NelsonW. Agbo^*and Stephen Amisah
Department of Fisheries and Watershed Management, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

Despite the fact that most plant ingredients (oilseed meals) are readily available at lower costs than fish meal, their use within aquafeeds is usually restricted by relatively low protein content, unbalanced essential amino acid profile, high levels of fibre and starch, especially non-soluble carbohydrates) and the presence of one or more endogenous antinutritional factors (ANFs). To improve the nutritive value of plant products, ingredients have been modified by chemical, mechanical and biological methods to remove antinutrients and/or fractions of low nutritive value which finally results in fairly good or high-protein plant products. This study evaluated the effect of processing of some oilseed meals (OSMs) namely; soybean meal (SBM), cottonseed meal (CSM) and groundnut meal (GNM) on their nutritional value and also on growth performance and cost-effectiveness when OSM-based diets were fed to Nile tilapia (Oreochromis niloticus).

These OSMs were detoxified by heat processing (autoclaving) and/or addition of phytase and ferrous sulphate to reduce levels of important ANFs in them. Seven isonitrogenous (320g.kg^-1) and isoenergetic (19.0kJ.g^-1) diets were formulated using equal mixtures (Q) of the OSMs as protein sources. The control diet was prepared with fish meal (FM) as source of protein while FM was substituted with 50% Q of the meals in the plant-based diets.

The results indicated that heat processing of the OSMs was very effective in reducing the trypsin inhibitors in SBM, CSM and GNM by 78.6%, 75.2% and 78.0% respectively but not the other ANFs and proximate composition (Table 1). Based on the growth performance and nutrient utilization Diet 2 (50% Q of processed OSMs) and Diet 5 (50% Q of unprocessed OSMs with phytase and ferrous sulphate supplementation) were better than the control diet. However, in terms of cost-effectiveness only Diet 2 was superior to the

control diet, meaning that simple heat processing alone could improve their utilization and cost-effectiveness (Table 2).