Adaptive mechanisms of rainbow trout to different salinity acclimation strategies: An integrated analysis from production performance, physiological biochemistry, transcriptomics

Developing effective salinity acclimation strategies can improve the welfare and farming efficiency of juvenile rainbow trout in mariculture. This study employed three acclimation groups and a freshwater control group: gradient salinity treatment (SG), acute salinity treatment (SA), gradient salinity with hydrocortisone supplementation treatment (SG_H), no salinity treatment (SC). The aim is to evaluate shared and specific adaptive mechanisms among different strategies through analysis of production performance, physiological and biochemical indicators, and gene expression. Results showed that survival rates and feed conversion efficiency were lower in all salinity-treated groups compared to the control group. At 7d, Mg 2 + concentrations were significantly lower in all salinity-treated groups compared to the SC ( P < 0.05 ). while the urea nitrogen and Na + concentrations were higher than those in the SC group. Transcriptome analysis indicates that ion transport and nitrogen metabolism as shared regulatory mechanisms across salinity treatments (SG_vs_SC, SA_vs_SC), driven by upregulation of genes including trpm7 , cftr , cps1 , atp1a1 . The SG group exhibited higher survival rates, feed conversion efficiency, ATP content than the SA group. KEGG analysis revealed significant enrichment in pathways related to energy metabolism, amino acid biosynthesis, driven by the significant upregulation of gstp , idh3a , and gulb genes. The SG_H group showed feed conversion efficiency was lower than the SG and SA groups. KEGG analysis indicated significant enrichment of the intestinal immune network for IgA production and Cytokine-cytokine receptor interaction pathways. This study provides molecular insights for developing salinity acclimation strategies in the saltwater farming of rainbow trout juveniles.