Effects of Protein and Lipid Levels in Extruded Pellets on the Growth and Body Composition of the Olive Flounder Paralichthys olivaceus during the Summer and Whiter Seasons

Feeding trials were performed at two different water temperatures (summer and winter seasons) to identify suitable protein and lipid (energy) levels to be used in formulating extruded pellets for olive flounder. Experiments were conducted to determine the effects of protein and lipid levels in extruded pellets on the growth and body composition of the flounder in both feeding trials. Six experimental diets were prepared containing three protein levels (46%, 51%, and 56%) and two lipid levels (10% and 17%). In the first experiment, during the summer season ($22{\pm}2.2^{\circ}C$), a triplicate group of fish (initial weight, 114 g) were fed to satiation one of the six diets for 11 weeks. The highest weight gain was observed in fish fed the 56/17 (% protein/% lipid) diet, but this weight gain was not significantly different from that of fish fed the other diets, except for those fed the 46/10 diet. The feed efficiency and protein efficiency ratio of fish fed the 17% lipid diets were higher than those of fish fed the 10% lipid diets at each protein level. In the second experiment, during the winter season ($13{\pm}1.5^{\circ}C$), a triplicate group of fish (initial weight, 107 g) were fed to satiation one of the six diets for 9 weeks. Weight gain was not significantly different among all groups. The feed efficiency and protein efficiency ratio tended to increase with increasing dietary lipid level at each protein level. The whole-body crude lipid content of the of fish fed the 17% lipid diets was significantly higher than that of fish fed the 10% lipid diets at each protein level in both feeding trials. Based on the data obtained in this study, the inclusion of dietary protein at a level of 46% appears to be sufficient to support optimal growth, and increasing the dietary lipid level from 10% to 17% had no beneficial effects on the growth and feed utilization of olive flounder (110-300 g), except for fish fed a 56% protein diet in the summer season.