Effects of salinity on growth performance, muscle quality, physiological biochemistry, and hepatic histology of Micropterus salmoides

Micropterus salmoides is an important freshwater commercial fish in China, and its aquaculture is expanding into low-salinity and saline-alkali waters. Salinity is a key environmental factor that plays a significant role in regulating its osmotic pressure, energy metabolism, growth, and development. To assess the effects of salinity on the growth, muscle quality, physiological and biochemical indicators, and liver tissue morphology of juvenile M. salmoides, we used four salinity treatments: 0, 3‰, 5‰, and 7‰. We systematically analyzed growth performance, muscle quality, physiological and biochemical indicators, and liver histology under these conditions. The results show that M. salmoides had superior growth performance at a salinity of 3‰, which was significantly higher than that at salinities of 0 and 7‰ (p<0.05), but not significantly different from that at salinity 5‰. Fish reared at salinity 3‰ also showed the greatest muscle hardness, chewiness, and adhesiveness, , significantly exceeding those at salinities of 0 and 7‰ (p<0.05), with no significant difference from those at salinity 5‰. Biochemical index analysis reveals that with increasing salinity, the reduced glutathione (GSH), malondialdehyde (MDA), low-density lipoprotein cholesterol (LDL-C), activities of superoxide dismutase (SOD), alkaline phosphatase (AKP), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) in serum increased significantly and reached their peaks at a salinity of 7‰. In contrast, catalase (CAT) activity and the contents of total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C) first increased and then decreased, with maximum values observed at a salinity of 3‰. Liver histology shows that higher salinity induces structural damage: hepatocytes at salinities of 0 and 3 remained intact and regularly arranged, those at salinity 5‰ showed mild vacuolation, and those at salinity 7‰ exhibited pronounced vacuolation and nuclear displacement. These findings enable the identification of an optimal salinity range conducive to the growth and quality enhancement of juvenile M. salmoides, providing a theoretical basis for its practical aquaculture.