1. Liaoning Key Laboratory of Protection and Utilization of Aquatic Germplasm Resource, Key Laboratory of Germplasm Improvement and Fine Seed Breeding for Marine Aquatic Animals, Ministry of Agriculture and Rural Affairs, Liaoning Ocean and Fisheries Science Research Institute, Dalian 116023, China; 2. Dalian Seafood Breeding Co., Ltd., Jinzhou 121000, China
Abstract：To understand the physiological response characteristics of rainbow trout Oncorhynchus mykiss juveniles during the salinity acclimatization, triploid rainbow trout juveniles weighing (40.0±6.5) g were placed in a continuous aerated circular tank with a diameter of 1.0 m and a depth of 1.2 m at initial salinity of 0, and then increased daily in 6 increments 2 days later until a salinity of 30 on the 5th day. The temporal changes in the enzyme activities related to antioxidant function, osmotic pressure regulation, and digestion were analyzed in the juvenile rainbow trout during the salinity gradient process, including superoxide dismutase (SOD) and catalase (CAT) in the liver and serum, the content of malondialdehyde (MDA), the activities of sodium-potassium ATPase (NKA) in the gill filaments and kidneys, and amylase (AMS), trypsin (TPS), and lipase (LPS) in the liver and intestines. The results showed that the content of MDA in serum and the activity of SOD were found to be significantly increased in the mid-period of salinity acclimation (P<0.05), and then to be returned to the initial level in the post-period of salinity acclimation, with the inverse relationship between activities of CAT and SOD during the salinity acclimation process. The content of MDA was shown to be significantly increased in the liver in both mid-phase and post-phase of the salinity acclimation (P<0.05), with the overall low content (less than 1.0 nmol/mg) and without significantly change in the activities of SOD and CAT in the liver, indicating that rainbow trout juveniles can eliminate excessive reactive oxygen species produced by the body′s stress during the salinity acclimation process through the synergistic action of antioxidant factors such as SOD and CAT, and that the blood is the main tissue for rainbow trout to eliminate oxidative stress and free radicals. The activities of NKA in kidneys and gills were fluctuated slightly during the salinization process, with slightly lower than the initial level at the end of the process, indicating that the later stage of salinization consumed less energy for osmotic pressure regulation and were able to adapt to higher salinity environments in rainbow trout. It was found that the activity of AMS in liver and intestine was fluctuated slightly during the salinization process and returned to the initial level and the activity of TPS increased significantly in the middle of the salinization process and returned to a level close to the initial level at the end of the process. The activity of LPS was found to be decreased significantly during the entire salinization process, significantly lower than the initial activity level at the end of the process, indicating that the salinization process led to little impact on the digestion of starch in rainbow trout juveniles, but enhanced the digestion of protein in the middle of the salinization process, suggesting that the salinization process may led to increase the demand for protein-based nutrients. The digestion of lipid-based nutrients was inhibited in rainbow trout by the salinization process. Therefore, it may be more beneficial for rainbow trout to undergo salinity acclimation by appropriately increasing the protein content of the feed and adding probiotic agents to the diet that have good lipid-degrading effects to promote the absorption and utilization of nutrients, as well as by adding appropriate amounts of antioxidants to diet to reduce the energy consumption of removing excess oxygen-free radicals from the body.
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2025, Vol. 44 
