Effects of nutrition-enriched Artemia nauplii on growth, digestive enzyme and associated hormones in tongue sole Cynoglossus semilaevis postlarvae

Effects of methionine enriched Artemia nauplii on growth performance, main digestive enzymes (amylase, acid protease, and alkali protease) activity, alkaline phosphatase activity and concentration of digestion related hormones (cholecystokinin, thyroxin, triiodothyronine, and cortisol) in Cynoglossus semilaevis Gunter (initial length 1.67±0.14cm) were studied. Three groups of postlarvae, including methionine group, Schizochytrium group, and methionine+Schizochytrium group, were fed Artemia nauplii enriched with methionine, Schizochytrium, and methionine+Schizochytrium respectively.A control group was fed Artemia nauplii without enrichment. Larvae were cultured for 16 days, sampled and tested at 4-day intervals. Postlarvae in the Schizochytrium treatment showed the highest growth at the end of the experiment;their weight was significantly greater than the control(P0.05), and their length was significantly greater than other treatments at 12d. Alkaline phosphatase activity in Schizochytrium treatment was significantly greater than the methionine treatment and the control at 16d (P0.05), and their alkali protease activity was significantly greater than the other treatments at 16d (P0.05). The concentration of triiodothyronine (T3) in Schizochytrium treatment was significantly higher than the methionine treatment and the control at 12d (P0.05). Thyroxin (T4) content in Schizochytrium treatment was significantly greater than the control at 12d (P0.05). Amylase activity in methionine+Schizochytrium treatment was significantly greater than the methionine treatment at 12d (P0.05). CCK level of the control was significantly higher than methionine+Schizochytrium treatment and methionine treatment at 4d (P0.05), and was significantly higher than the other treatments or Schizochytrium treatment at 12d and 16d. No significant differences were found in acid protease activity between four different treatments. Cortisol levels of methionine treatment was significantly lower than the other treatments at 4d, and significantly lower than the control and methionine+Schizochytrium treatment at 8d and 16d (P0.05). However, alkaline phosphatase, amylase activity, T3 and T4 levels were higher at the earlier stages of the experiment. It is suggested that methionine-enriched Artemia nauplii feeding can meet the growth requirement of C. semilaevis larvae.