Abstract:This study was conducted to evaluate the potential of replacing fish meal with ribose protein in juvenile turbot (Scophthalmus maximus L.). A single factor experiment -with six fish meal levels was used. A control diet (D1) was formulated to contain 45% fish meal. In other five diets, 44.5% (D2), 44% (D3), 43% (D4), 42% (D5), and 41% (D6) of the fish meal in the diet control were replaced with ribose protein, respectively. Each diet was randomly fed to triplicate groups of 30 fish per tank. The experimental period was 56 d. The results showed that as the replacement ratio of fish meal by ribose protein increased, the weight gain rate (WG), specific growth rate (SGR), and protein efficiency ratio (PER) showed a trend of first rising and then decreasing, they were all significantly higher in the D3 group than in the D5 and D6 groups (P<0.05). However, the feed conversion ratio reached a minimum in the D3 group. Compared with the control group, the serum IGF-1 and GH contents in the replacement groups were significantly decreased (P<0.05). Trypsin activities of the intestine in D3, D4, and D5 groups were significantly higher than in other groups (P<0.05). Amylase activities in the intestine of the D3 and D4 groups were significantly higher than that in the control group (P<0.05). Lipase activity reached a minimum in the D3 group (P<0.05). The total protein, globulin, and alkaline phosphatase contents in the replacement groups were significantly higher than those in the control group (P<0.05). The lysozyme activity in the D3 group was significantly higher than that in the D6 group (P<0.05). The albumin content and the activity of superoxide dismutase were not significantly different among all the groups (P>0.05), while the serum IL-1β and TNF-α contents were significantly increased (P<0.05). Compared with the control group, the total cholesterol and triglyceride contents in the D4, D5, and D6 groups were significantly decreased (P<0.05). The serum low-density lipoprotein cholesterol content of the D5 and D6 groups was significantly decreased (P<0.05), and the serum high-density lipoprotein cholesterol content of the D4 group was significantly increased (P<0.05). Glucose content first increased and then decreased as the replacement ratio of fish meal by ribose protein increased, and it was the highest in the D3 group (P<0.05). The challenge study showed that the D2 group had a lower cumulative mortality rate than other groups after 48 hours (P<0.05). It can be concluded that the optimum level of replacing fish meal in turbot diet with ribose protein is 1% based on growth performance, and simultaneously considers the indices of digestion and specific immune, and disease resistance in S. maximus under this experimental condition.
