Abstract: Total dissolved gas (TDG) supersaturation caused by dam sluicing can result in gas bubble trauma (GBT) in fish and threaten their survival. In the present study, Chinese suckers (Myxocyprinus asiaticus Bleeker) were exposed to TDG supersaturated water at levels ranging from 120% to 145% for 48 h. The median lethal concentration (LC₅₀) and the median lethal time (LT₅₀) were determined to evaluate acute lethal effects on Chinese suckers. The results showed that the LC₅₀ values of 4, 6, 8, and 10 h were 142%, 137%, 135%, and 130%, respectively. The LT₅₀ values were 3.2, 4.7, 7.8, 9.2, and 43.4 h, respectively, when TDG supersaturated levels were 145%, 140%, 135%, 130%, and 125%. Furthermore, the biological responses in Chinese suckers were studied by assaying the catalase (CAT) activities in gills and muscles at the supersaturation level of 140% within LT₅₀. The CAT activities in the gills and muscle tissues exhibited a regularity of a decrease after an increase. CAT activities in the muscles were increased significantly at 3/5LT₅₀ (P<0.05) and then came back to the normal level. However, there were no significant differences between the treatment group (TDG level of 140%) and the control group (TDG level of 100%) on CAT activities in the gills before 3/5LT₅₀ (P>0.05), but the activities were significantly lower than the normal level at 4/5LT₅₀ and LT₅₀ (P<0.05).

Key words: Total dissolved gas supersaturation, Median lethal time (LT₅₀), Median lethal concentration (LC₅₀), Chinese sucker, Catalase

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