Effects of low salinity exposure on osmotic regulation, physiological metabolism, oxidative stress, health status, and apoptosis in Haliotis diversicolor.

Low salinity exposure triggers a series of physiological responses in marine mollusks, whereas the underlying regulatory mechanism in Haliotis diversicolor-a stenohaline marine gastropod with an optimal growth salinity of 30-35‰-under low-salinity conditions remain unclear. In this study, H. diversicolor was exposed to acute low-salinity conditions for 96 h at salinities of 18, 20, and 22‰, with natural seawater at 30‰ as the control. Physiological and histological indices were determined at 12, 24, 48, 72, and 96 h, and multivariate analyses were performed using PCA and DFA.Low salinity exposure inhibited total ATPase and Na+/K+-ATPase activities and decreased hemolymph osmolality, indicating impaired osmoregulatory function. Glucose, triglyceride, and total cholesterol levels increased markedly and peaked at 72 h, reflecting enhanced energy mobilization for osmotic adaptation. Activities of SOD, CAT, and GSH-Px decreased, while ROS and MDA levels increased, suggesting oxidative damage. Elevated AST, ALT, AKP, and ACP activities indicated systemic physiological disturbance and impaired health status. After 96 h, gill and hepatopancreas tissues showed vacuolization, inflammatory infiltration, and swelling, accompanied by increased caspase 3 activity and TUNEL-positive signals.This study clarifies the physiological and tissue structural responses of H. diversicolor to acute low-salinity stress through systematic physiological and histological analysis, thereby revealing its adaptive and damage mechanisms under salinity fluctuation. These findings provide a direct scientific basis for optimizing salinity management in abalone aquaculture and formulating targeted culture strategies to improve survival and support sustainable healthy farming of H. diversicolor.