Study on the physiological and molecular regulatory mechanisms of Sinonovacula rivularis in response to low-salinity stress

The euryhaline bivalve Sinonovacula rivularis exhibits remarkable adaptability to low-salinity stress, yet its integrated physiological and molecular mechanisms remain incompletely understood. This study systematically investigated its physiological responses and transcriptional regulatory strategies under acute low-salinity conditions (0 ‰ salinity) using physiological profiling and transcriptomic analyses. Under low-salinity stress, significant gill filament swelling and transient respiratory suppression within the initial 12 h were observed. During 12–24 h of exposure, ammonia excretion rates surpassed control levels, accompanied by markedly reduced oxygen-to-nitrogen ratios. Heart rates declined progressively after 24 h, indicating prioritized energy allocation toward osmoregulation and amino acid metabolism. Transcriptomic analysis identified 3011, 804, and 443 differentially expressed genes (DEGs) at 12, 24, and 72 h post-exposure, respectively. These DEGs were predominantly enriched in glutathione metabolism, amino acid biosynthesis, and ion transport pathways. Key genes involved in energy metabolism ( PKM , PEPCK , PRKAA2 ), taurine synthesis ( CSAD , CDO1 ), free amino acids metabolism ( CRANS1 , CA1 , GAUD1 ), antioxidant defense ( GSTP1 ), and ion transport ( CLCN7 , SLC9A2 , KCNN3 ) were significantly upregulated. Conversely, downregulation of SLC8A1 , a gene associated with cardiac rhythm regulation, likely contributed to the sustained heart rate decline post-24h. Weighted Gene Co-expression Network Analysis (WGCNA) revealed core gene modules linked to energy metabolism, ion transport, and amino acid homeostasis. These findings demonstrate that S. rivularis employs a multi-layered adaptive strategy, involving accelerated amino acid turnover, structural gill modifications, and transcriptional regulation of free amino acids metabolism, energy pathways, and ion transport. This work enhances our understanding of molluscan euryhaline adaptation and provides a theoretical foundation for breeding salinity-tolerant aquaculture species and managing estuarine ecosystems under climate change. • The transcriptome of Sinonovacula rivularis was analyzed under low-salinity stress for the first time. • Integrated physiological, transcriptomic analyses & WGCNA revealed key molecular mechanisms for low-salinity adaptation in S. rivularis . • Multi-layer adaptive strategies: enhanced amino acid metabolism, gill structure changes, osmoregulatory pathway transcriptional regulation.