Growth rate,feed utilization and energy metabolism of the African catfish,Clarias gariepinus (Burchell, 1822), as affected by dietary protein and energy content

Three feeding experiments were conducted in open circuit balance respirometers, to determine the effect of dietary protein level on growth rate, feed utilization and energy metabolism of Clarias gariepinus (Burchell). The feeding level was 2% of the fresh body weight per day. Three energy levels, 8.4, 12.6 and 16.8 kJ calculated metabolizable energy (ME) per gram of feed, were used, while crude protein levels in the diets were 20, 25, 30, 35 and 40%.Growth rate, heat production, metabolizability (ME as percentage of gross energy intake) and protein gain were maximal at the intermediate energy level. Digested protein per gram of growth was lowest at this energy level (determined ME = 13 kJ/g). Growth rate, metabolizability and protein gain increased as protein intake increased. There was no effect of the different protein levels on heat production. The efficiency of protein gain (% of the digestible protein intake) was highest (45–49%) at the intermediate energy level. Efficiency of protein gain (% of digestible intake) decreased slightly when protein intake increased. ME intake per gram of growth was minimal at the 8.4 kJ energy level and decreased at higher protein intake levels.At the highest energy level, growth rate was reduced compared to the intermediate energy level, but efficiency of energy gain, retention of fat and energy were highest. Much of the dietary fat was deposited as lipid reserves. After 4 weeks the growth rate, digestibility, metabolizability, and efficiency of protein- and energy gain (% of digestible or metabolizable intake respectively) were strongly reduced at this energy level.