From waste to feed: Dietary utilisation of bacterial protein from fermentation of agricultural wastes in African catfish (Clarias gariepinus) production and health

A feeding trial was conducted to evaluate the effects of replacing fish meal (FM) with bacterial protein (BP) in African catfish (Clarias gariepinus) diets. Four iso‑nitrogenous (369 g kg⁻¹) and isolipidic (142 g kg⁻¹) diets were formulated to replace graded levels (0%, 30%, 60% and 100%) of FM protein resulting in a dietary inclusion level of 0, 27.90, 55.70 and 93.00 g kg⁻¹ BP. Test diets were fed to the catfish (initial weight 18.17 ± 0.25 g fish⁻¹, n = 20) in three replicate tanks. After 56 days of feeding, catfish fed with 30% BP diet had outperformed (P < 0.05) fish that were fed with the control diet (100% FM) in mean weight gain (MWG), percentage weight gain (PWG), specific growth rate (SGR) and metabolic growth rate (MGR). However, the growth response (MWG, PWG, SGR, and MGR) from diets containing 60% and 100% BP did not differ significantly to the dietary control. The whole-body protein (+8%) and lipid (+12%) contents of the catfish fed 30% BP diet were higher (P < 0.05) than no BP inclusion dietary group. The replacement of FM with BP in the catfish diets did not statistically affect the haematological status (P > 0.05). While histological analysis of the catfish mid-intestine showed intact epithelial barriers with extensive mucosal folds extending into the lumen. The intestinal perimeter ratio of fish fed with 30% BP diet was higher (+32%) than those of the dietary control group (P < 0.05), but not differ from 100% BP-fed diet (P > 0.05). Indication of the liver health status was measured through serum aspartate transaminase, alanine transaminase, and alkaline phosphatase activities, and hepatocyte density, which remains statistically unchanged between the dietary groups (P > 0.05). Overall, the results show that BP can replace FM wholly or partly in African catfish (C. gariepinus) diet, without compromising growth performance, haemato-biochemistry, intestinal integrity, or liver functionality.