Growth rate,catalase and superoxide dismutase activities in rock carp(Procypris rabaudi Tchang) exposed to supersaturated total dissolved gas

Total dissolved gas supersaturation(TDGS) appears when the pressures of gases in a solution exceed the barometric pressures.TDGS is often caused by flood discharge at dams.It may lead to gas bubble disease(GBD) for fish and biochemical responses of selected fish and other aquatic organisms.The purpose of this study was to determine the impact of long-term TDGS levels on the growth and biochemical responses of rock carp(Procypris rabaudi Tchang) dwelling in the upper reaches of the Yangtze River.Three-year-old rock carp were exposed to TDGS levels at 100%,104%,108%,112%,and 116% for 42 d.Samples were taken every 7 d after the start of the trial in order to determine catalase(CAT) and superoxide dismutase(SOD) activities in gill and muscle tissues.Samples were taken at Days 0 and 42 of exposure to determine growth rate.Little effect was found on growth rate in all treatment groups.SOD and CAT activities varied in different tissues,according to time of exposure and TDGS levels.The biochemical response of fish exposed to TDGS was more obvious in gill tissue than in muscle tissue.Surveys of SOD and CAT activities in different tissues offer important information about the effect of TDGS on the rare fish in the Yangtze River,and may help evaluate the risk to the aquatic eco-environment and aquatic ecosystem in the downstream of the Yangtze River.

Effect of total dissolved gas supersaturated water on early life of David's schizothoracin (Schizothorax davidi)

The effect of total dissolved gas （TDG） supersaturation on fish living downstream of dams is one of the main ecological risks of high dam construction. A strategy for mitigating the negative effects is needed urgently since many high dams are under construction in the upper reaches of the Yangtze River in China. Experiments on the hatching process of David＇s schizothoracin were carried out and the results show that the hatching rate decreased with increasing TDG levels, and that most eggs hatched within a very short time in the higher TDG saturation groups. By using a stereomicroscope, damages to the head, yolk sac, body, anus, etc. were found in larvae which hatched in TDG supersaturated water. Results show that the lesion rate increased with increasing TDG levels. Furthermore, 7-d-old David＇s schizothoracin were exposed to TDG supersaturated water levels of 100%, 105%, 110%, 115%, 120%, 125%, 130%, 135%, and 140% for testing their tolerance to TDG supersaturation. We found that the median lethal concentrations （LC50） for 13, 14, 20, 35, 52, 73, and 96 h exposure were 138%, 138%, 134%, 130%, 129%, 128%, and 126%, respectively. The median lethal times （LTs0） were 7.49, 11.04, 19.25, and 35.38 h for exposure to water with TDG levels of 145%, 140%, 135%, and 130%, respectively.