The Repairing Effect of Arginine on Soybean Meal-Induced Enteritis of Sebastes schlegelii

The complete intestinal structure is important to ensure the rapid and h ealthy growth of fish. However, the feed composition, aquaculture water environment, intestinal microbial population, and other factors may affect the intestinal health of fish. Intestinal health problems caused by feed ingredients are mainly due to the antinutrient factors contained in raw materials. Antinutritional factors contained in high-level soybean meal can cause oxidative damage to the intestine, thus, inducing soybean meal-induced enteritis (SBMIE), which leads to a decreased appetite and the slow growth of fish. Alleviating the damage of soybean meal to the fish intestinal tract and improving intestinal health through nutrition are essential methods for ensuring the sustainable development of the feed industry, which has significant ecological and economic significance.As a functional amino acid, arginine is a precursor to the synthesis of bioactive substances, such as urea, glutamic acid, creatine, proline, polyamine, and nitric oxide. Arginine modulates metabolic regulation, including growth, immunity, intestinal barrier, and endocrine regulation. It plays a vital role in the immune regulation, maintenance, and protection of the intestinal mucosal structure and function. It has been reported that arginine is beneficial for repairing intestinal mucosal injury in poultry and aquatic animals. In this study, the carnivorous marine economic fish Sebastes schlegelii (54.97±0.12) g were used to investigate the repair effect and mechanism of arginine on SBMIE. This study aimed to provide a scientific basis for the application of arginine for maintaining the intestinal health of fish and provide a reference for the application of plant protein to the compound feed of the carnivorous economic fish S. schlegelii.The purpose of this study was to investigate the repairing effects of arginine on the growth performance, arginine metabolism, intestinal structure, antioxidant performance, relative expression levels of intestinal tight junction protein genes (occludin, clnd15, and zo-1), and inflammatory factor-related genes (il-1β, il-8, il-15, and tlr8) and anti-inflammatory factor-related gene (il-12b) of S. schlegelii with SBMIE. S. schlegelii were fed high-level soybean meal (40%) for 28 days to induce SBMIE. SBMIE-S. schlegelii weighing (54.97±0.12) g were used as the study animals. Four isonitrogen and isoenergetic experimental feeds were formulated. The basic formula was supplemented with 30% soybean meal, arginine 0 supplementation as the control group (D0), and 1%, 2%, and 3% arginine supplementation as the treatment groups, named D1, D2, and D3, respectively. Each diet group had three replicates, and each replicate consisted of 40 fish. The fish were randomly placed in 12 homemade cages (60 cm × 60 cm × 90 cm). The experiment lasted for 6 weeks. The experimental fish were fed twice a day (08:00 and 17:00), with the initial feeding amount being 1% of the body weight, and the feeding amount being adjusted according to the feeding situation. During the experiment, the bottom of the cages was cleaned, and the water was changed every day to maintain the water temperature at 18~22 ℃, the dissolved oxygen at > 6 mg/L, the pH at 7.6~8.2, the ammonia nitrogen content at < 0.05 mg/L, and the nitrite nitrogen content at < 0.05 mg/L. The light cycle was the natural cycle. The results showed that the weight gain rate of the fish in the D2 and D3 groups was significantly higher than that in D0 group (P < 0.05). The hepatosomatic and viscerosomatic indexes of the fish in the arginine treatment groups were significantly lower than those in the D0 group, and the condition factor was significantly higher than that in the D0 group (P < 0.05). There was no significant effect on the survival rate (P > 0.05). Diamine oxidase (DAO) activity, NO content, and iNOS activity values in the serum of the treatment groups were significantly lower than those in the D0 group (P < 0.05). The serum T-NOS activity in the D2 and D3 groups was significantly lower than that in the D0 group (P < 0.05). The duplicature height in the treatment groups was significantly higher than that in the D0 group, while no significant difference was found in the duplicature number and muscle thickness (P > 0.05). In group D0, the intestinal mucosa lamina propria widened, and the number of goblet cells increased, while in groups supplemented with arginine, the intestinal mucosa was intact, and the problems mentioned above improved significantly. Intestinal total antioxidant capacity (T-AOC) in arginine supplementation groups was significantly increased, and the highest value was found in group D2 (P < 0.05). The malondialdehyde content in groups D2 and D3 was decreased significantly compared to that in the D0 group (P < 0.05). The relative expression of occludin mRNA in each treatment group was significantly upregulated compared to that in the D0 group (P < 0.05). The relative expression level of clnd15 mRNA in the D2 group was significantly higher than that in the D0 and D1 groups (P < 0.05). The relative expression level of zo-1 mRNA in group D1 was significantly higher than that in the other groups (P < 0.05). The relative expression levels of IL-1β, IL-15, and TLR8 mRNA were downregulated in all treatment groups, while the relative expression of IL-12b mRNA was upregulated (P < 0.05). No significant differences were found in IL-8 mRNA relative expression (P > 0.05). In conclusion, under the conditions of this experiment, the growth and antioxidant performances of S. schlegelii with SBMIE were significantly increased, arginine metabolism and the intestinal structure were improved significantly, and the relative expression of intestinal tight junction protein and anti-inflammatory factor-related genes was upregulated, while that of inflammatory factor-related genes was downregulated, with arginine supplementation in a high-level soybean meal diet. Arginine (2% best) was effective in repairing SBMIE of S. schlegelii. The results of this study provide a theoretical basis for the mechanism of repairing SBMIE with arginine.