Effects of dietary L‐tryptophan supplementation on growth performance, food intake, digestive enzyme activity and serotonin (5‐HT) levels in juvenile Chinese mitten crab ( Eriocheir sinensis )

This study was designed to evaluate the effects of dietary L-tryptophan (L-trp) supplementation on growth performance, feeding and digestion, 5-HT levels and the related receptor expression levels of Eriocheir sinensis. In this study, crabs were divided into four groups: the analysed tryptophan concentrations were 3.6 (Diet #A), 4.7 (Diet #B), 7.3 (Diet #C) and 10.5 (Diet #D) g/kg dry matter, respectively. In Trial 1, we found that there was no significant difference in the growth parameters (weight gain rate, carapace length increase rate, carapace width increase rate and hepatopancreas index) among the four dietary groups after 30 days, whereas the molting rate was significantly higher in the Diet #C group and the limb autotomy rate was significantly lower in the Diet #C group than in the Diet #A group (p < .05). Moreover, trypsin activity and lipase activity were significantly improved. In Trial 2, we found that dietary L-trp supplementation after 7 days significantly increased the feeding rate and motor behaviour duration of E. sinensis. In Trial 3, we found that 5-HT levels in haemolymph increased dose dependently with dietary L-trp supplementation and were significantly higher in the Diet #D group than in the Diet #A group (p < .05). Moreover, the expression trends of 5-HT 1BR in the hepatopancreas, thoracic ganglia and cranial ganglia; 5-HT 2BR in the thoracic ganglia; and 5-HT 7R in the hepatopancreas, intestine and cranial ganglia were similar to the change trend of 5-HT levels. In conclusion, dietary L-trp supplementation was beneficial for molting cycle and can significantly improve food intake and digestive enzyme activities possibly by mediating 5-HT and binding to its related receptors, which will provide new insights into the physiological functions of L-trp in E. sinensis.