Comparative transcriptomic analysis reveals osmoregulatory mechanisms of juvenile Lateolabrax maculatus responses to long term hypotonic and hypertonic acclimation

Salinity limits the abundance and distribution of some fishes in a particular ecological niche. The spotted sea bass (Lateolabrax maculatus), an euryhaline species, exhibits remarkable adaptability to various salinity levels. To elucidate the osmoregulation mechanisms of this species, the growth performance, serum biochemical parameters and gill transcriptomic profiles of the juvenile spotted sea bass subjected to long term hypotonic (0 ppt) and hypertonic environment (30 and 45 ppt), with the isotonic environment (12 ppt) as the control, were investigated. During the 30 days' salinity acclimation, the growth performance of the juvenile sea bass was inhibited significantly (P < 0.05) at hypertonic condition of 45 ppt, while no significant differences were observed among those at 0, 12, and 30 ppt. The serum biochemical indicators of plasma osmolality, concentration of Na⁺, Cl⁻, glucose, urea, total protein, and ALT and AST activities significantly increased during the hypertonic acclimation. Transcriptome analysis identified 1179, 103, and 443 differentially expressed genes in the 0, 30, and 45 ppt salinity groups, respectively, compared to the isotonic (12 ppt) group. Bioinformatics analysis revealed that signal transduction pathways were promoted during hypotonic acclimation, while energy metabolism pathways were activated during hypertonic acclimation. Protein-protein interaction and WGCNA analysis identified hub genes that may play important functions during acclimation. Among them, protein synthesis related-genes including Rps15, Rps16, Rps9, Rpl4, Rpl15, Rpl30, Rpl31, Rpl13a and Eef2 were down-regulated under hypotonic acclimation, metabolic related-genes including Cs, Idh2, Idh3, Mdh2, Pck1, Pck2, Pdha1 and Ldhb were up-regulated under the hypertonic condition. Rac1 were up-regulated in both conditions. This study provides new insights into the osmoregulatory mechanisms of spotted sea bass in response to long-term hypotonic and hypertonic acclimation.