Approaches to optimizing dietary protein to energy ratio for African catfish Clarias gariepinus (Burchell, 1822)

An 8‐week feeding trial was conducted in a recycling water system at 28 ± 1 °C to investigate protein to energy ratio (P/E ratio) in African catfish Clarias gariepinus (10.9 ± 0.04 g). Six fishmeal‐based diets of two protein levels (330 and 430 g kg −1 ), each with three lipid levels (40, 80 and 120 g kg −1 ) resulted in P/E ratios ranging from 15.5 to 21.3 mg protein kJ −1 gross energy (GE) were fed to 20 fish (per 30‐L tank) in triplicate. Fish were fed 50 g kg −1 of their body weight per day adjusted fortnightly. Significantly higher ( P  < 0.05) growth rates and feed conversion efficiency were evident in fish fed with higher protein diet. The highest growth rate was found by fish fed 430 g kg −1 protein, 21.2 kJ −1 GE with a P/E ratio of 20.5 mg protein kJ −1 GE. Significantly indifferent ( P  > 0.05) values of protein utilization were found in‐between the both (higher and lower) protein diets. Higher lipid deposition ( P  < 0.05) in whole body and liver was observed with increasing dietary lipid level at each protein diet and as higher ( P  < 0.05) for the lower protein diets. Liver glycogen tended to decrease with increasing gross energy at each protein diet and higher protein diet showed comparatively lower values ( P  > 0.05). Digestive enzyme activities (protease and lipase) and histological examination of intestine and liver of fish fed varying P/E diets found no significant differences in response to experimental diets. The study reveals that African catfish C. gariepinus performed best the diet containing 430 g kg −1 , 21.2 kJ g −1 and 20.5 mg protein kJ g −1 GE protein, gross energy and P/E ratio, respectively.