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 degrees 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.