Abstract:
Objective Acute toxicity of elevated salinity on juvenile Silurus lanzhouensis was studied to determine the range of the stress-tolerance of the fish.
Method Based on the LC50 and the safe concentration (SC) obtained from an initial toxicity determination test, randomized groups of fish in 3 replicates per group were raised in tanks with waters of 10‰ salinity for 24, 48, 72, and 96 h, along with 0 h for control. Pathological observation and measurements of activities of superoxide dismutase (SOD), catalase (CAT), and lactate dehydrogenase (LDH) as well as content of malondialdehyde (MDA) in the gill, liver, and kidney were conducted to determine the responses of the fish to the imposed salt-stress.
Result Under the stress of high salinities, the juvenile S. lanzhouensis showed LC50 at 24, 48, 72 h, and 96 h of 12.71‰, 12.11‰, 11.49‰ and 10.88‰ salt, respectively, and the SC was 3.46‰. Histopathological observations showed that salt-stress caused swelling and curling of gilllets edema, vacuolization of hepatocytes, and necrosis of renal tubules. And the tissue damage increased in severity as the stress prolonged. There were no significant enzyme activity changes in the gill under the stress for 24–48 h; however, after 72 h, the activities of SOD, CAT, and LDH as well as the content of MDA rose significantly (P≤0.05). In the liver, the enzyme activity fluctuated and peaked in 24 h and 72 h followed by a decline.
Conclusion S. lanzhouensis was salt-tolerant to a certain degree so long as the water salinity did not exceed 3.46‰. High salt content in aquaculture pond invariably disrupted the antioxidant balance and energy metabolism that triggered progressive damage in multiple organs, and ultimately, led to total failure of the normal physiological functions of the fish. This study demonstrated the range of salinity in which juvenile S. lanzhouensis could survive. The information was of value for proper aquacultural practice, evaluation of saline and alkaline waters in the middle and upper reaches of the Yellow River for aquaculture, and breeding of resilient varieties of fish.
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