Food utilization by red tilapia — Effects of diet composition, feeding level and temperature on utilization efficiencies for maintenance and growth

Abstract

Routine metabolism and utilization of food were determined for red tilapia. Two experiments were performed, each in 24 tanks of 450 l, covered to prevent photosynthesis and the development of natural food. The average temperatures during the experiments were 24.3 and 20.9°C. Routine metabolism was determined by starving two groups of fish of average body weights 15.2 and 79.7 g in the first experiment and 18 and 58.3 g in the second, for 4 weeks. Energy equivalents were calculated by means of proximate analyses. Weight loss was highest in moisture, followed by protein and lipid. Specific routine metabolism for a 1 g fish was 36.7 cal/day at the higher temperature and 25.4 cal/day at the lower temperature.

Maintenance metabolism was determined by feeding the fish three diets of varying protein contents — 43.9% (high protein = HP), 28.7% (medium protein = MP), and 13.1% (low protein = LP), at three levels — 0.5, 1 and 3% of wet body weight per day. The higher the protein content in the diet, the more water and protein but less lipid was saved from being metabolized. No differences in the efficiency of utilization of the diets for maintenance were observed. The specific maintenance level for fish of 1 g was about 73 cal/day of metabolizable energy at 24.3°C, and about 51 cal/day at 20.9°C. A considerable difference was observed in the efficiency of food utilization for growth. The high protein diet (HP) was more efficient than MP and LP diets at the higher temperature. At the lower temperature the efficiency of the HP diet decreased while that of the LP and MP diets increased.