Effects of corn starch level on growth performance, antioxidant capacity, gut morphology and intestinal microflora of juvenile golden pompano, Trachinotus ovatus

Carbohydrates are the cheapest source of dietary energy for fish. Utilization of carbohydrates in feed is beneficial to sparing protein consumption as energy source and saving feed cost. Therefore, 8-week feeding experiment was conducted to investigate the effects of starch level on growth performance, antioxidant capacity, serum biochemical parameters, intestinal morphology and intestinal microbiota of Trachinotus ovatus. Six isonitrogenous and isolipidic diets (D1, D2, D3, D4, D5 and D6) containing 0%, 5%, 10%, 15%, 20% and 25% corn starch were formulated, respectively. Each diet was randomly assigned to triplicate groups of fish (initial body weight 11.84 g) fed twice daily to apparent satiation. Results showed that percent weight gain, specific growth ratio, hepatosomatic index, total antioxidation capacity and glutathione content of fish fed with D6 diet were the highest among all experimental treatments. Feed conversion rate was significantly lower in fish fed with D5 and D6 diets, than in fish fed with D1-D4 diets. No significant differences were found in the survival rate, viscerasomatic index, malondialdehyde and serum triglyceride contents among all diet treatments. The superoxide dismutase activity of T. ovatus fed with D3-D6 diets were relatively higher than those fed with D1 and D2 diets. Fish fed with D3 diet showed the highest value of serum total cholesterol. High-density lipoprotein cholesterol / low-density lipoprotein cholesterol ratio of fish fed with D1 and D6 diets were relatively higher than those fed with D2-D5 diets. No significant pathological changes in the foregut were observed among all diet treatments. Dietary starch level lead to alterations in the intestinal microbiota in T. ovatus. D2-D5 dietary treatments increased the abundance of harmful bacteria such as Vibrio, Photobacterium, Mycoplasma. D1 and D6 dietary treatments had similar intestinal microbiota composition. In conclusion, 25% starch level was beneficial to the growth and health of T. ovatus. •5%–25% starch level had no adverse effect on growth and antioxidant capacity of T. ovatus.•5%–20% starch level increased the abundance of harmful bacteria.•25% starch level was beneficial to the growth and health of T. ovatus.