| The largemouth bass is a major economic fish species in our country, possessing a certain degree of salt tolerance. It has great potential for aquaculture in saline-alkali water. It is of vital importance to explore the osmoregulation and physiological responses of largemouth bass under different salinity stresses. This study focused on largemouth bass with an average weight of 20.3±1.3 g and conducted stress experiments under various salinity groups (0 ppt, 5 ppt, 10 ppt, and 15 ppt), examining their serum biochemical indicators, osmoregulation enzyme activities, antioxidant enzyme activities, tissue pathological changes, and relative expression levels of NKCC1a. The results showed that the serum osmolality, Na+ concentration, Cl- concentration, and serum cortisol concentration of the largemouth bass all increased to varying degrees with the rise in salinity, with significant differences between the 15 ppt group and the 10 ppt, 5 ppt, and control groups (P<0.05). Compared to the control group, the activities of Na+/K+-ATPase（NKA）、Ca2+-Mg2+-ATPase（CMA）and Catalase（CAT）were significantly increased at salinities of 5 ppt and 10 ppt, reaching a peak at 10 ppt. However, the NKA, CMA and SOD significantly decreased compared to 10 ppt at a salinity of 15 ppt (P<0.05). Histological observations of the gills and intestines revealed that the number of chloride cells and goblet cells increased in the gills and intestines at 15 ppt and 10 ppt, with even tissue necrosis and cell shedding, while the gills and intestines at 5 ppt were unaffected. Besides, the expression levels of NKCC1a in the gills and intestines showed tissue specificity, and the expression levels of NKCC1a at 5 ppt, 10 ppt, and 12 ppt were consistently significantly higher than those in the control group (P<0.05). Furthermore, correlation analysis showed that COR was highly correlated with the expression of NKCC1a in Na?, K?, Cl?, Ca2? and gill (r≥0.8). In summary, the largemouth bass showed good adaptability at a salinity of 5 ppt, while the salinities of 10 ppt and 15 ppt can have certain effects on the physiological responses and gene expression of largemouth bass. The results of this study can provide reference and data support for the culture and development of largemouth bass in brackish water environments. |
