[Antioxidant responses of rainbow trout with different ploidies to acute temperature stress.]

Rainbow trout (Oncorhynchus mykiss) is a cold-water fish species with optimal temperature of 12-18 ℃. Temperature stress is a common issue in commercial culture of the Salmonid fish in summer. Both maple trout and steelhead trout are rainbow trout breeding species with good quality. The purpose of this study was to explore the impact of acute temperature stress on antioxidant responses of two kinds of rainbow trout. The juvenile maple trout was diploid, and the juvenile steelhead trout was triploid. The fishes were exposed to four different temperature treatments: 13, 17, 21, and 25 ℃, and hepatic samples were collected at 0, 1, 6, and 12 h. After acute heat stress, the fish were transferred to the tank with optimal temperature (13 ℃) and hepatic samples were collected after 1, 12, 24, and 48 h. The biomarkers, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), lipid peroxidation (LPO), malondialdehyde (MDA), and heat shock protein 70 kDa (HSP70) were measured. Results showed that the activities of SOD, CAT, and GPx in both maple trout and steelhead trout in 17 ℃ treatment had no significant increase after acute temperature stress. The SOD activities of maple trout and steelhead trout in 21 ℃ treatment significantly increased in response to acute temperature stress, but the SOD activity of maple trout returned to normal during the recovery process. The activities of SOD, CAT, and GPx for both species in 25 ℃ treatment were significantly increased after acute temperature stress, which returned to normal for 24 h recovery. The amount of HSP70 produced by maple trout at 17, 21, and 25 ℃ treatments was significantly higher than that at 13 ℃ treatment, while that of steelhead trout was significantly higher for the 21 and 25 ℃ treatments than that at 13 ℃ treatment. A variety of antioxidant parameters were analyzed by integrated biomarker response (IBR) values. Results showed that the antioxidant response of maple trout was significantly higher than that of steelhead trout in 17 ℃ and 21 ℃ treatments, but significantly lower than steelhead trout in 25 ℃ treatment. Such a result indicated that the antioxidant responses of different ploidy rainbow trouts were different under acute stress at different temperatures.