EFFECT OF FISH PROTEIN HYDROLYSATE LEVELS ON GROWTH PERFORMANCE AND BIOLOGICAL AND PHYSIOLOGICAL PARAMETERS IN TONGUE SOLE (CYNOGLOSSUS SEMILAEVIS G躈THER, 1873) POST-LARVAE

This study evaluated the effects of fish protein hydrolysate inclusion in the diet of tongue sole (Cynoglossus semilaevis Günther, 1873) post-larvae on growth performance, the activities of alkaline phosphatase (AKP) and the digestive enzymes: pepsin, trypsin, lipase and amylase and intestine development in the fish. Four experimental diets were formulated by supplementing 0% (FM), 20% (FPH-20), 40% (FPH-40) and 60% (FPH-60) of FPH in the diet. Each diet was randomly assigned to triplicate groups of fish, and each group was stocked with 60 tongue sole post-larvae (30 days post-hatching, with an initial dry weight of 6.47±0.38 mg) in 12 fiberglass tanks (50 cm×40 cm×20 cm). Fish were fed four times daily (05:00, 10:00, 15:00 and 21:00) to visual satiation for 28 days. During the feeding trial, water temperature and salinity were maintained at (22±1℃) and 30—32, respectively. At the end of the 28-day growth experiment, survivals of the fish were relatively high and ranged from 64.44% to 78.88%. Fish fed diets with 20% and 40% FPH showed significantly higher survival rates than other two groups Cynoglossus semilaevis. Compared to the control, 20% FPH supplementation in the diet improved growth of the tongue larvae while high dose of FPH depressed that concerning the values of specific growth rate (SGR); the activities of digestive enzymes, such as lipase, amylase, pepsin and trypsin showed no obvious trends among all treatments between 14 and 28 d, respectively; the AKP activity in all groups were ordered as follows (P40% FPH>0% FPH>60% FPH; fish fed the diet with 20% FPH showed significantly higher intestinal villus and thicker mucosa than the other three groups (P<0.05). In this study, the diet with 20% of the FPH gave the best results in terms of growth, survival and intestinal development in tongue sole post-larvae, indicating FPH had a nutritional value equivalent to fish meal (FM).