Combined Transcriptomic and Histological Profiling Uncover Hepatic Regulatory Hierarchy of Triploid Oncorhynchus mykiss Under Interactive Salinity, Temperature and Body Weight Regimes.

Salinity, temperature and body weight dominate seawater acclimation in rainbow trout (Oncorhynchus mykiss), yet few studies simultaneously explore their main effects and potential correlative interactive patterns in hepatic responses. A 60-day L9 (33) orthogonal trial was performed on triploid rainbow trout with three gradients of body weight, temperature and salinity. Hepatic transcriptomics revealed that salinity drove global transcriptional remodeling and high salinity induced far fewer DEGs than medium salinity. WGCNA screened a salinity-positive blue module (r = 0.408, p = 0.0346), while alternative splicing confirmed extensive salinity-dependent post-transcriptional regulation. Semi-quantitative histology showed that 20 °C was associated with more pronounced salinity-caused hepatocellular vacuolation and karyopyknosis in the orthogonal test. Survival statistics indicated that salinity was the only factor with significant main effects (p < 0.05), and the 500 g-10 °C-10 ppt group obtained the highest survival. This multi-omics and histological dataset reveals a suggestive regulatory hierarchy-like pattern: salinity acts as the primary driver, temperature serves as a synergistic amplifier, and body weight plays a minor modulatory role. These findings provide a theoretical basis for developing size-specific salinity acclimation protocols in commercial triploid rainbow trout farming.