In this study, we investigated the effects of acute low-salt stress on the survival, plasma osmolality, blood ion concentration, and Na+/K+-ATPase activities of two sizes of black sea bream (Acanthopagrus schlegelii). The acute toxicity test revealed a significant difference in the 96 h semi-lethal salinity between 5 cm (0.264) and 10 cm (1.096) juveniles of A. schlegelii. However, no significant difference was observed in the safe salinity values between the two groups. Analysis of plasma osmotic pressure and blood ion concentrations showed an overall trend of first decreasing, then increasing, and finally stabilizing. Under environmental stress at salinities of 1, 3, 5, and 10‰, the plasma osmotic pressure of 5 and 10 cm A. schlegelii stabilized after 12 h and 24 h for all salinities, respectively, with isosmotic points of 11.48 and 11.66. For 5 cm A. schlegelii, blood Na+ stabilized after 24 h and Cl– stabilized after 12 h for all salinities, and Ca²+ stabilized after 24 h, respectively. In contrast, for 10 cm A. schlegelii, blood Na+ stabilized after 48 h, Cl– stabilized after 48 h, respectively, and Ca²+ stabilized after 48 h, respectively. These results demonstrate that 5 cm juveniles achieved osmotic and ionic equilibrium significantly faster than 10 cm fish, facilitating rapid ion homeostasis. The Na+/K+-ATPase activity in gills and kidneys generally exhibited a trend of first increasing, then decreasing, and finally stabilizing. The enzyme activity trend in the intestine showed the opposite pattern, and its Na+/K+-ATPase activity increased under low-salinity conditions. Na+/K+-ATPase activity in the gills, kidneys, and intestines of 5 cm A. schlegelii reached equilibrium faster than those of 10 cm A. schlegelii. In conclusion, 5 cm juvenile A. schlegelii exhibited superior low-salinity tolerance, accelerated osmoregulatory responses, and enhanced adaptation efficiency compared to 10 cm A. schlegelii. Practically, for low-salinity culture (≤ 3‰) or rapid transfer scenarios, stocking smaller juveniles (around 5 cm) or implementing a longer stepwise acclimation for larger juveniles is recommended to reduce acute mortality and shorten the time to osmotic stabilization.

Effects of Low Salinity Stress on the Survival and Osmotic Regulation of two Sizes of Juvenile Acanthopagrus schlegelii

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发表日期：

2026年2月27日

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Zhichang Yuan,
Yiming Li,
Yan Li,
Pengcheng Gao,
Chaofeng Jia,
Qian Meng,
Dan Guo,
Zongli Yao,
Qifang Lai

摘要

In this study, we investigated the effects of acute low-salt stress on the survival, plasma osmolality, blood ion concentration, and Na⁺/K⁺-ATPase activities of two sizes of black sea bream (Acanthopagrus schlegelii). The acute toxicity test revealed a significant difference in the 96 h semi-lethal salinity between 5 cm (0.264) and 10 cm (1.096) juveniles of A. schlegelii. However, no significant difference was observed in the safe salinity values between the two groups. Analysis of plasma osmotic pressure and blood ion concentrations showed an overall trend of first decreasing, then increasing, and finally stabilizing. Under environmental stress at salinities of 1, 3, 5, and 10‰, the plasma osmotic pressure of 5 and 10 cm A. schlegelii stabilized after 12 h and 24 h for all salinities, respectively, with isosmotic points of 11.48 and 11.66. For 5 cm A. schlegelii, blood Na⁺ stabilized after 24 h and Cl^– stabilized after 12 h for all salinities, and Ca²⁺ stabilized after 24 h, respectively. In contrast, for 10 cm A. schlegelii, blood Na⁺ stabilized after 48 h, Cl^– stabilized after 48 h, respectively, and Ca²⁺ stabilized after 48 h, respectively. These results demonstrate that 5 cm juveniles achieved osmotic and ionic equilibrium significantly faster than 10 cm fish, facilitating rapid ion homeostasis. The Na⁺/K⁺-ATPase activity in gills and kidneys generally exhibited a trend of first increasing, then decreasing, and finally stabilizing. The enzyme activity trend in the intestine showed the opposite pattern, and its Na⁺/K⁺-ATPase activity increased under low-salinity conditions. Na⁺/K⁺-ATPase activity in the gills, kidneys, and intestines of 5 cm A. schlegelii reached equilibrium faster than those of 10 cm A. schlegelii. In conclusion, 5 cm juvenile A. schlegelii exhibited superior low-salinity tolerance, accelerated osmoregulatory responses, and enhanced adaptation efficiency compared to 10 cm A. schlegelii. Practically, for low-salinity culture (≤ 3‰) or rapid transfer scenarios, stocking smaller juveniles (around 5 cm) or implementing a longer stepwise acclimation for larger juveniles is recommended to reduce acute mortality and shorten the time to osmotic stabilization.