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Osmoregulation and Physiological Response of Largemouth Bass (Micropterus salmoides) Juvenile to Different Salinity Stresses

Year: 2025

Type: article

Abstract: The distribution of saline-alkali water is extensive and increasing globally each year. Fully utilizing saline-alkali water for aquaculture can help alleviate the scarcity of freshwater resources in global fisheries. As a major economic fish species, the largemouth bass (Micropterus salmoides) holds significant potential for aquaculture in saline-alkali water. In the present study, we evaluated its tolerance to different salinities (0 ppt, 6 ppt, 9 ppt, 12 ppt, 15 ppt, and 18 ppt) and investigated tissue pathology, serum biochemical indicators, enzyme activities of osmolality and antioxidant, and the relative expression of Na-K-2Cl 1a cotransporter (NKCC1a) under different saline stress (0 ppt, 6 ppt, 9ppt and 12 ppt). The largemouth bass 96 h mortality rate increased with increasing salinity, and the LC50 for 96 h was 14.28 ppt based on the mortality results. The histological observations of gill and intestinal tissues were consistent with the mortality results. Specifically, the number of gill chloride cells and intestine goblet cells of 12 ppt and 9 ppt increased and showed tissue necrosis and cell shedding, while the gill and intestine of 6 ppt were unaffected. Besides, the serum osmolality, iron content (Na+ and Cl-), and cortisol concentration of largemouth bass showed varying degrees of increase from 12 to 48 h, with significant differences observed between the 12 ppt group, and the 9 ppt, 6 ppt, and control groups (p < 0.05). In addition, the activities of Na+/K+-ATPase (NKA) and Ca2+-Mg2+-ATPase (CMA) in the gill and superoxide dismutase (SOD) in the liver showed a trend of first increasing and then decreasing within 48 h, reaching a peak at 24 h, and the activity increased with the increase of salinity. Furthermore, the expression level of NKCC1a in the gill was higher than that in the intestine, with the expression level of NKCC1a at 9 ppt and 12 ppt consistently significantly higher than the control group (p < 0.05), indicating its crucial role in osmoregulation. In conclusion, largemouth bass can be healthily cultured at 6 ppt salinity and selectively bred for salt tolerance at 9 ppt salinity. The activity of NKA, cortisol concentration, and NKCC1a expression level increase with higher salinity in 96 h, which can be used as reference indicators to evaluate salt tolerance. Taken together, the findings of this study provide guidance for the practical rearing of largemouth bass in saline waters and contribute to research on stress physiology.

Source: International Journal of Molecular Sciences

DOI: 10.3390/ijms26083847