Effects of acute salinity stress on the physiological and biochemical characteristics of juvenile golden trevally (Gnathanodon speciosus)

Objective Golden trevally (Gnathanodon speciosus) is an emerging warm-water marine species of aquacultural and ornamental value in China, and its salinity adaptability is an important factor affecting its environmental adaptation. This study aims to investigate the physiological responses of juvenile G. speciosus to acute salinity stress.

Methods Three salinity treatments were established: 15 (low-salinity group), 30 (control group), and 45 (high-salinity group). After 24 h of acute salinity stress, survival rates were recorded, and antioxidant, nonspecific immune, and osmoregulatory-related indicators were determined in the gill, intestine, and kidney tissues.

Results The survival rate of juveniles was 100% in the control group, and 93.3% and 86.7% in the low- and high-salinity groups, respectively, indicating that high-salinity stress had a more pronounced adverse effect on juvenile survival. In the gills, catalase (CAT) and superoxide dismutase (SOD) activities and hydrogen peroxide (H₂O₂) content were significantly higher in the control group than in the low- and high-salinity groups (P<0.05), whereas total antioxidant capacity (T-AOC) and malondialdehyde (MDA) levels were significantly elevated in the high-salinity group (P<0.05). Acid phosphatase (ACP), alkaline phosphatase (AKP), and Na⁺/K⁺-ATPase (NKA) activities all exhibited clear salinity-dependent responses. In the intestine, CAT and SOD activities and T-AOC levels were highest in the control group, whereas MDA content was significantly elevated in the high-salinity group (P<0.05); meanwhile, ACP, AKP, and NKA activities were all significantly enhanced under high-salinity stress (P<0.05). In the kidney, ACP activity was significantly decreased in both the low- and high-salinity groups (P<0.05), whereas AKP activity showed no significant difference among the groups (P>0.05).

Conclusion Acute salinity stress affected the survival and physiological status of juvenile G. speciosus. The survival rate decreased to 86.7% under high-salinity stress, accompanied by significant increases in MDA content in the gill and intestine (P<0.05), indicating a relatively greater impact of high-salinity stress on the juveniles. In the kidney, the response was mainly characterized by a significant decrease in ACP activity (P<0.05). These findings demonstrate tissue-specific responses of juvenile G. speciosus to acute salinity stress and provide a basis for further elucidating the mechanisms of salinity adaptation and salinity tolerance in this species.