Physiological Response Mechanisms of Triplophysa strauchii Under Salinity Stress

Salinity, a critical environmental factor for fish survival, remains poorly understood in terms of how Triplophysa strauchii, a characteristic fish in Northwest China, physiologically responds to salinity stress. This study aimed to determine its salinity tolerance threshold and explore the associated physiological damage mechanisms. Six salinity gradients (11, 11.7, 12.5, 13.3, 14.3, 15.1 ppt) and a freshwater control group were established. Acute toxicity tests recorded mortality and behavior, while physiological-biochemical assays measured ion concentrations and enzyme activities in gills, kidneys, liver, intestines, and plasma over 96 h. The results showed a 96-hour median lethal concentration of 13.31 ppt and a safe concentration of 4.05 ppt. Gills and kidneys, as primary osmoregulatory organs, responded rapidly, whereas the liver and intestine lagged. Salinity ≤ 13.3 ppt allowed the fish to maintain homeostasis via physiological adjustments, but ≥14.3 ppt caused ion imbalance, immune function was significantly suppressed, and irreversible damage. These findings clarify the species' salinity adaptation strategies, providing a basis for further research on chronic salinity stress.