Effects of dietary succinic acid supplementation on growth performance, digestive ability, intestinal development and immunity of large yellow croaker (Larimichthys crocea) larvae.

The application of artificial micro-diet is an effective way to improve and standardize the quality of aquatic animal larvae. However, the widespread adoption of micro-diet faces a bottleneck due to the limited utilization capacity of the larvae. A 30-day feeding experiment was carried out to investigate the effect of dietary succinic acid (SA) on the growth performance, digestive ability, intestinal development, and immunity of large yellow croaker larvae (initial body weight 11.33 ± 0.57 mg). Four isonitrogenous and isolipidic diets were formulated, incorporating 0.00 %, 0.01 %, 0.02 % and 0.03 % SA separately. The results showed that a diet with 0.02 % SA significantly increased both the final body weight and the specific growth rate of the larvae. Regarding digestive ability, 0.01 % SA supplementation significantly enhanced trypsin activity in both intestinal and pancreatic segments. In addition, 0.01 % SA supplementation notably improved amylase activity in the intestinal segment, while diets with 0.01%-0.02 % SA significantly improved lipase activity in the pancreatic segment. In terms of intestinal development, 0.01 % SA supplementation remarkably boosted the activities of alkaline-phosphatase and leucine-aminopeptidase on brush border membrane in intestine. Furthermore, 0.03 % SA supplementation significantly increased the expression of occludin. In terms of immunity, larvae fed diets with 0.01%-0.02 % SA exhibited significantly higher lysozyme activity compared to the control group. Supplementation with 0.01 % SA also significantly increased both iNOS activity and NO content. In summary, the findings of this study suggested that supplementing 0.02 % SA can improve the growth performance of large yellow croaker larvae by improving digestive enzymes activities, promoting intestinal development, and enhancing nonspecific immunity.