Partial use of groundnut cake as an alternative protein source to fish meal in diets of juvenile nile tilapia (Oreochromis niloticus).

In this study, the effects of diets prepared using groundnut cake (GNC) instead of fish meal on growth performance, fillet composition, amino acid profile, fatty acids, digestive enzymes and histological parameters in juvenile Nile tilapia (Oreochromis niloticus) were investigated. In the experiment, which lasted 80 days and in which the average water temperature was 27 ± 1 °C, 30 tilapia with an average weight of 9.85 g were stocked in each 450-L tank. Experimental groups were planned as follows: control (0% GNC), GNC10 (10% GNC), GNC20 (20% GNC), GNC30 (30% GNC), and GNC40 (40% GNC), each with three replicates. Growth performance was maintained up to the 20% inclusion level, with final weight, weight gain and specific growth rate in the GNC20 group comparable to the control (p > 0.05), whereas marked reductions occurred at 30% and particularly 40% inclusion (p < 0.05). Feed conversion ratio and protein efficiency ratio followed the same pattern, and survival was 100% in all groups. The ratio of essential amino acids to non-essential amino acids in muscle was highest in the GNC20 group (0.84 ± 0.01) (p < 0.05). In muscle, Ʃn3, Ʃn6 and the n3/n6 ratio did not differ significantly among groups (p > 0.05), whereas docosahexaenoic acid decreased and total monounsaturated fatty acids increased at the highest inclusion level (p < 0.05). Digestive enzyme activities responded in a tissue-specific manner: hepatic amylase and lipase peaked at the 10% inclusion level and declined thereafter, whereas intestinal protease increased at the 30% and 40% levels; hepatic protease was unaffected (p > 0.05). Histological examination revealed no pathological alterations in muscle tissue, and hepatic vacuole parameters did not differ significantly among groups (p > 0.05), although liver crude fat content increased with dietary GNC (p < 0.05). In the intestine, overall size parameters were significantly reduced in all GNC groups, while villus number, villus length and villus-to-perimeter ratio were unaffected (p > 0.05). Under the conditions of the present study, fish meal can be replaced with up to 20% GNC in juvenile Nile tilapia diets without impairing growth performance, feed utilisation or tissue integrity.