Comparative studies on the nutrition of two species of abalone, Haliotis tuberculata L. and Haliotis discus hannai Ino. IV. Optimum dietary protein level for growth

A 100 day growth experiment was conducted to identify the optimum dietary protein level for the juveniles of two species of abalone, Haliotis tuberculata and Haliotis discus hannai. A mixture of vitamin-free casein and gelatin (4.34:1) supplemented with crystalline amino acids was used as the protein source to simulate the amino acid profile of abalone body. Eight purified diets were formulated to provide graded protein levels ranging approximately from 0 to 50%. The weight gain, protein gain, soft body to shell ratio, and carcass levels of protein and lipid of both abalone species were significantly (ANOVA, P < 0.05) affected by the dietary protein level. The protein requirements of these abalone were evaluated from weight gain and protein gain respectively, by using the second-order polynomial regression analysis. On the basis of weight gain, the optimum protein levels were estimated to be 22.3-32.3%, and 23.3-35.6% for H. tuberculata and H. discus hannai, respectively. According to the protein gain, the statistical analysis indicated that the optimum ranges of protein requirements were 24.0-34.5% and 25.2-36.6% for H. tuberculata and H. discus hannai, respectively. Based on these results, about 35% dietary protein from good quality sources is recommended for the maximum growth of both abalone species; and, if dietary protein is reduced from 35 to 25%, the growth of these abalone may be depressed with 5% likelihood.