Studies on the nutrition of spotted sand bass Paralabrax maculatofasciatus: Effect of the dietary protein level on growth and protein utilization in juveniles fed semipurified diets

Two feeding trials were conducted to determine the digestibility of a casei n-based semipurified diet and the effects of different protein levels on gr owth and protein use of spotted sand bass Paralabrax maculatofasciatus juve niles. For trial I, a semipurified diet with vitamin-free casein as the sol e source of protein was fed three times a day to apparent satiation, for a period of 20 d, Feces were collected by siphoning each tank. The digestibil ity of the experimental diet was high: 97% for protein, 89% for lipids, and 84% for gross energy, whereas that of organic matter was 78%. For trial II , seven diets mere formulated using vitamin-free casein at graded levels (2 5, 30, 35, 40, 45, 50, and 55% protein). Triplicate tanks for each dietary treatment were stocked with fish and fed by hand three times a day to appar ent satiation for 6 wk, Performance of fish fed the different diets was eva luated for survival, percent weight gain, specific growth rate, feed conver sion ratio, and protein efficiency ratio. Survival was 100% for all treatme nts. Growth of spotted sand bass juveniles increased as the dietary protein increased, but no evidence of reaching a plateau was found, The daily feed intake values showed an inverse relation to the protein content of the die ts. The feed conversion ratio did not differ among diets containing 40% pro tein or greater. The results indicate that spotted sand bass juveniles with 2.5-g mean weight need at least 55% dietary protein for best growth when c asein is the sole protein source. However, in terms of feed conversion rati o, the requirement apparently could be lower.