The growth performance, antioxidant capacity, liver fat metabolism and intestinal flora composition responsiveness to fish meal replacement by peanut cake for juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

This experiment was conducted to determine the optimum amount of peanut cake (PNK) in the diet of hybrid grouper by studying the effect of PNK on the growth, antioxidant capacity, liver fat metabolism, and intestinal microbiota composition by replacing fish meal (FM) protein in the diet of the juvenile hybrid grouper. A total of 840 juvenile hybrid grouper with uniform body weight (13.20 ± 0.05 g) were selected from 7 treatments and 4 replicates (30 fish each) farmed for eight weeks. Results showed that the weight gain rate (WGR) of the low-substitution group was significantly higher than that of the high-substitution group (P < 0.05) and that the feed conversion and specific growth rates of the 44%, 55%, and 66% groups were significantly higher than those of the other groups (P < 0.05). The crude lipid content of the 44% group was significantly higher than those of other groups (P < 0.05), and the crude protein content of the 66% group was lowest and significantly lower than that of the control group (P < 0.05). The total protein content showed a decreasing trend and then an increasing trend. The total cholesterol content showed a gradually decreasing trend and was significantly higher in the control and 11% groups than those in the other groups (P < 0.05). The glutamic oxalacetic transaminase content in the 66% group was significantly higher than those in other groups (P < 0.05). The total antioxidant capacity and the malondialdehyde content of the 66% group were significantly higher (P < 0.05) and significantly lower (P < 0.05), respectively, than those of other groups. The oil red-stained sections of the liver showed that the deposited fat gradually increased with increasing levels of PNK replacement in the diet. A replacement level higher than 22% caused a decrease in WGR. When the replacement level was higher than 44%, a significant increase (P < 0.05) in harmful bacteria in their intestines was observed, and when the replacement level was higher than 55%, a significant increase (P < 0.05) in liver fat accumulation was observed. Based on the PNK replacement level corresponding to WGR, the appropriate PNK replacement level in the diet was 15%.