Effect of salinity exposure on the antioxidant system of “Taihu No. 3” Macrobrachium Nipponense

China possesses vast saline-alkaline water resources, necessitating their utilization. Macrobrachium nipponense, an economically important freshwater shrimp with notable salinity tolerance, is a candidate for saline aquaculture. This study determined the 96-h LC₅₀ of salinity for the genetically improved "Taihu No. 3" strain juveniles across a gradient (0-30 parts per thousand) and investigated associated stress responses. Morphological, physiological, and molecular responses were analyzed via antioxidant enzyme activity (glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT), superoxide dismutase (SOD), malondialdehyde (MDA)) and immune gene expression in hepatopancreas and gills. Results showed the 96-h LC₅₀ was 11.841 ppt, significantly lower than wild populations, suggesting enhanced energy allocation towards growth over osmoregulation in "Taihu No. 3". Acute and chronic stress significantly elevated GPx, GR, CAT, SOD activities and MDA levels (P < 0.05), indicating their critical role in mitigating oxidative damage and maintaining homeostasis. Salinity ≥ 10 ppt induced structural damage, including hepatopancreatic basement membrane disruption and gill alterations (enlarged interlamellar spaces, epithelial swelling). Chronic exposure significantly upregulated immune genes (CAT, Mn-SOD, Cu/Zn-SOD) in both tissues (P < 0.05), demonstrating their involvement in saline acclimation. These findings define measurable salinity tolerance limits and elucidate key immune response mechanisms in "Taihu No. 3", providing a scientific basis for its cultivation in saline-alkaline aquaculture.