Digestibility of nutrients and energy in diets for the African catfish Clarias gariepinus (Burchell 1822)

A purified diet, the raw material zein, and two diets composed of complex foodstuffs (fishmeal, soy, wheat) were tested for eight months in the African catfish Clarias gariepinus (Burchell 1822) to determine the in vivo Apparent Digestibility Coefficients (ADC) for dry matter, crude protein, lipid, carbohydrates, ash, energy, and amino acids. Feces were collected by sedimentation and digestibility coefficients were calculated using chromium oxide as an external indicator. Average ADCs ranged 54-96%. The ADC of crude protein (80-90%) was similar to previously recorded ADCs. Ash digestibility (54-89%) varied significantly between diets, probably as the result of the reduced bioavailability of minerals and trace elements in the constituent raw materials. ADC for individual amino acids ranged 82-99%. Zein, as an experimental feed ingredient, had an acceptable ADC for both gross nutrients and amino acids. When the nutrient level in the test ingredient differed greatly from that in the reference diet, calculation of ADC was based on relative nutrient contributions. Results are discussed in relation to the nature of the dietary ingredients and their suitability for related experimental nutritional work.