The Function of Tryptophan Hydroxylase in Regulating Agonistic Behavior of the Chinese Mitten Crab (<i>Eriocheir sinensis</i>)

Agonistic behavior is common among crustaceans, but it presents risks such as energy loss, injury, and even death in aquaculture settings. Our previous study indicated that l-tryptophan (l-TRP) inhibits agonistic behavior in <i>Eriocheir sinensis</i>. However, supplementing l-TRP in diets increases costs and reduces nutritional quality. This study explores the role of tryptophan hydroxylase (TPH) in l-TRP metabolism and its regulation of agonistic behavior in <i>E. sinensis</i>. Our results show that l-TRP supplementation significantly increases the serotonin level and TPH expression. Subcellular localization confirmed the expression of the TPH in the cytoplasm of HEK293T cells. RNA interference of TPH significantly enhanced in the contact numbers of the crabs. While overexpression of the TPH significantly inhibited agonistic behavior in <i>E. sinensis</i>. Specifically, the fight duration was reduced from 6.67 ± 2.03 min in the control group to 1.81 ± 0.39 min, and the fight number decreased from 17 ± 2.47 to 8.0 ± 1.27. Moreover, the concentration of serotonin in <i>E. sinensis</i> was increased after TPH overexpression. Additionally, fluoxetine injection also significantly inhibited the agonistic behavior. In summary, our findings suggest that TPH regulates agonistic behavior in <i>E. sinensis</i> by mediating the conversion of l-TRP into 5-HT.