Gill histological, biochemical and transcriptomic responses of Coregonus ussuriensis to acute salinity stress

Abstract

Salinity is a key environmental factor affecting the osmoregulation and physiological homeostasis in freshwater fish. Juvenile Coregonus ussuriensis has been considered a candidate species for culture in moderately saline waters, but its short-term physiological and molecular responses to salinity remain poorly understood. In this study, C. ussuriensis were exposed to 0‰, 14‰ and 20‰ salinity for 96 h, and gill histology, apoptosis, antioxidant and immune-related enzyme activities, ion-transport activity and transcriptomic profiles were examined. Acute salinity exposure induced lamellar edema, curvature and epithelial hyperplasia, with more severe lesions observed at 20‰. TUNEL staining showed a salinity-dependent increase in the apoptotic index. CAT, T-AOC and Na + /K + -ATPase activities increased under salinity stress, whereas SOD, LDH and MDA showed decreasing trends. Transcriptomic analysis identified differentially expressed genes mainly associated with ion transport, oxidative phosphorylation, immune-related signaling and energy metabolism. qRT-PCR validation generally supported the RNA-seq expression patterns. These results suggest that gill ion transport, antioxidant regulation, immune modulation and metabolic adjustment contribute to the short-term salinity response of juvenile C. ussuriensis . In conclusion, this study provides new insights into the salt tolerance mechanism of the C. ussuriensis and valuable information for its saltwater aquaculture.