Effects of MS-222 on anesthetic effect, tissue structure and liver antioxidation of juvenile Eleutheronema tetradactylum

【Objective】 To investigate the effects of MS-222 on the anesthesia effects, gill tissue damage, and liver antioxidant capacity of juvenile Eleutheronema tetradactylum, which could provide scientific reference for research on stress resistance of Eleutheronema tetradactylum and the application of MS-222 as an aquatic product anesthetic. 【Method】 Using juvenile Eleutheronema tetradactylum with an average body length of 6.0±0.3 cm and an average body weight of 1.6±0.3 g as experimental material, with a control group receiving no anesthetic and no aeration, the staticwater anesthesia effects of different MS-222 mass concentrations（10, 15, 20, 25, 30, 40, 50 mg/L） on the juvenile Eleutheronema tetradactylum at 30 and 35 ℃ were analyzed. Based on their behavioral responses in the MS-222 anesthetic solution, the MS-222 mass concentration were further refined. Additionally, the antioxidant enzyme activity in the liver of juvenile Eleutheronema tetradactylum were measured and histological observations of their gill tissues were conducted. 【Result】 Under the conditions of 30 and 35 ℃, with the increase of MS-222 mass concentration, the time for juvenile Eleutheronema tetradactylum to enter the same anesthesia period greatly decreased; the optimal anesthesia mass concentration for juvenile Eleutheronema tetradactylum using MS-222 was 14 mg/L, and the survival rates of juvenile Eleutheronema tetradactylum after continuous anesthesia for 12 h and 24 h after recovery were 100.0%; the activities of liver antioxidant enzymes in different concentration groups of MS-222 showed obvious differences. Compared with the control, catalase（CAT） activity was increased, while superoxide dismutase（SOD） activity was decreased. Observing the pathological sections of juvenile Eleutheronema tetradactylum tissues, it was found that as the mass concentration of MS-222 increased, gill fragments exhibited bending, swelling at the end, and in severe cases, swelling and detachment. When using MS-222 at a concentration of 14 mg/L to simulate transportation in still water for 6 h, gill fragments showed slight bending, oedema, and tight arrangement. However, these conditions improved after 12 h of simulated transportation. 【Conclusion】 Different mass concentrations of MS-222 exhibit sedative effects on juvenile Eleutheronema tetradactylum. Under both 30 and 35 °C conditions, the optimal anesthetic dosage for juvenile Eleutheronema tetradactylum is determined to be 14 mg/L, which effectively reduces stress responses to external stimuli.