Pheromone screening and neuro-endocrine regulation in turbot (Scophthalmus maximus) under different stocking density

AbstractPheromones play a vital role in regulating fish behavior, including reproduction, aggregation, hazard recognition, and food location. To gain a better understanding of chemical communication in fish produced by density changes, this study analyzed the metabolites released by turbot (Scophthalmus maximus) under different stocking density and investigated their effects on the neuroendocrine function of turbot. The experiment was conducted at low (LD: 3.01 kg/m3), medium (MD: 6.62 kg/m3), and high (HD: 10.84 kg/m3) densities for 15 days. High-throughput non-targeted metabolomics (LC-MS/MS) was used to identify variations in metabolites released into the aquatic environment by turbot at different densities. Results showed that 29 and 47 metabolites were significantly upregulated in MD and HD groups, respectively, compared with the LD group. Among them, hexadecanedioic acid, xanthine, phenethylamine, proline, and styrene were significantly upregulated in MD vs LD, HD vs MD, and HD vs LD. The VIP diagram of OPLS-DA alignment showed that phenethylamine was the most important metabolite shared by MD vs LD, HD vs MD, and HD vs LD. To investigate the impact of phenethylamine on turbot, its concentration in the aquatic environment was set at 0 (CON), 10− 7(LP), 10− 5(HP) mol/l via exogenous addition, and turbot were exposed to these environments for 2 days. Key genetic changes in the GH/IGF-1 signaling pathway, HPI axis of turbot were studied using qRT-PCR for density treatment and phenethylamine treatment. The results demonstrated that the expression of GH, GHR, and IGF-1 was significantly lower, while the expression of CRH and ACTH was higher in the HD group. Additionally, plasma levels of cortisol, glucose, triglycerides, and T3were also highest in the HD group compared to the LD and MD groups and were positively correlated with density. In the phenethylamine treatment, there was a high degree of concordance between the GH/IGF-1 signaling pathway (GH, GHR, IGF-1), HPI axis (CRH, ACTH) and plasma physiological changes (cortisol, glucose, triglycerides, T3) in the phenethylamine-treated group and the density-treated group. Thus, phenethylamine produced by turbot under high stocking density may act as a pheromone of density stress, and its effect is dose-dependent and trace effect.