Abstract:Spotted halibut, Verasper variegates has been a target model in the studies of reproductive biology and molecular biology. However, litter is known about the dietary requirements of this species. In this study, we determined the optimal ratio of protein to lipid for this fish and analyzed the combined effects on the growth，digestive enzyme activities and blood biochemical parameters in spotted halibut. Fish meal and casein were used as protein sources, and soybean oil and fish oil served as lipid sources. Nine experimental diets were formulated as combinations of three levels of crude proteins (40%, 45%, and 50%) and three levels of crude lipid (8%, 12%, and 16%), namely P40L8, P40L12, P40L16, P45L8, P45L12, P45L16, P50L8, P50L12 and P50L16. They were randomly distributed into 27 cement ponds (2 m×1 m×1 m) with 20 fish/pond for 83 d in an in-door flow-through aquarium system. The results showed that the survival rate of fish was not significantly affected by the levels of protein and lipid (P>0.05). The weight gain, specific growth rate and feed intake were significantly reduced along with the increase in the dietary lipid (P<0.05). Compared to P40L16, the weight gain in P50L8 was 33.63% higher and the specific growth rate was 31% higher. The feed efficiency was significantly boosted along with the increase in the dietary protein (P<0.05). The feed efficiency in P50L8 was 24.09% higher than P40L8, and the weight gain, specific growth rate, feed intake and feed efficiency in P50L8 were significantly higher than those in other groups. The activity of stomach protease was first increased and then decreased along with the increase in dietary protein. The protease activity in the hepatopancreas in P50L8 group was significantly higher than that in P50L12 group (P<0.05), but showed no significant differences with other groups (P>0.05). The activity of the stomach lipase was first decreased and then increased along with the increase in the dietary protein. The activity of intestine lipase in P50L8 group was higher than other groups, but there was no significant difference between all groups (P>0.05). The increase in dietary protein resulted in significantly higher level of total proteins (P<0.05). Glutamic pyruvic transaminase and Glutamic oxalacetic transaminase in P50L8 group were higher than other groups, but there were no significant differences between all groups (P>0.05). Triglyceride and total cholesterol in P50L8 group were significantly lower than P45L12 and P45L16 groups (P<0.05), but showed no significant differences with other groups (P>0.05). These results indicated that increased dietary lipid level might not cause the protein-sparing effect. Therefore the recommended formula for the best growth performance was 50% protein, 8% lipid, 104.31 mg/kcal P/E and 6.63 P/L.
