Energy utilisation efficiencies of digestible protein, fat and carbohydrates for African catfish (Clarias gariepinus)

Abstract

In this study, the effect of dietary macronutrient composition on the energy utilisation efficiency for growth using the digestible energy (DE) approach was evaluated for African catfish (Clarias gariepinus). Furthermore, the energy utilisation efficiencies of digestible protein, fat and carbohydrates for growth were estimated using the net energy (NE) approach. The experiment had a 4 × 2 factorial design. C. gariepinus (71.6 g) were fed one of four diets, each at two feeding levels (12 vs 22 g.kg−0.8.d−1), for 30 days. Diets were formulated with the aim to create large contrasts in the digestible protein (dCP), fat (dFat) and carbohydrate (dCarb) content among the four diets. These contrasts in dietary composition and feeding levels enabled multiple regression analysis of energy retention (RE) as a function of dCP, dFat and dCarb intake. Using the DE approach, the dietary macronutrient content affected the energy utilisation efficiency (kgDE) of C. gariepinus. Increasing the dietary carbohydrate content reduced the kgDE from 93.5% to 78.5% in low starch diets compared to high starch diets. Thus the relationship between DE and RE is affected by the dietary macronutrient composition. With the NE approach, energy utilisation efficiencies of digestible protein, fat and carbohydrates for growth of C. gariepinus were estimated at 86%, 95% and 59%, respectively. Results of the present study indicated the probability of biases in feed evaluation and formulation when using the DE approach. Thus the NE approach is advisable as means for energy evaluation of feed/ingredients for C. gariepinus.