Biochemical responses and survival of rock carp (Procypris rabaudi) to total dissolved gas supersaturated water

Abstract

Total dissolved gas (TDG) supersaturation resulting from spillway discharge during high flows can cause gas bubble disease (GBD) and mortality in fish, and increases threats to their survival. In recent years, TDG supersaturation has become a severe eco-environmental problem owing to the construction of a number of high dams in China. The aim of this study was to investigate the impact of long-term TDG supersaturation on survival and biochemical responses in endemic species dwelling in the upper Changjiang (Yangtze) River. Juvenile rock carps (Procypris rabaudi) were subjected to chronic exposure of TDG supersaturated water at low levels (104, 108, 112 and 116 % respectively), whereas a control group was given vacuum-degassed water (100 % TDG level). The mortality rate of the fish and catalase (CAT) and superoxide dismutase (SOD) activity in various tissues were measured to evaluate survival and biochemical responses in juvenile rock carp exposed to TDG supersaturated water. The results showed that some symptoms of GBD were observed in rock carp exposed to TDG supersaturated water, but no mortality was found due to GBD. Furthermore, TDG supersaturation caused an increase of CAT and SOD activity in muscle and gill tissues of the rock carp. The capacity to generate CAT and SOD activity at the 112 % and 116 % levels was 1.5-fold to 1.9-fold higher than that in the control group after 21 days of exposure. The increase of CAT and SOD activity was not significant at the 104 % level during the exposure period. However, this increase suggested oxidative stress in cells and also reflected the important role that CAT and SOD perform in removing excess reactive oxygen species from cells. These findings can help us to evaluate how seriously the fish are damaged by TDG supersaturated water and may offer valuable information for the formulation of water quality standards and the protection of aquatic organisms in China.