Morphology And Physiological Response Of Juvenile Grass Carp To Ammonia Nitrogen Stress

Fish farming is one of the main uses of natural water in China. As the common pollutants in water environment, ammonia have negatively effect on the growth of aquatic organisms. The morphological and physiological effects of the low concentration of ammonia nitrogen on aquatic organisms for long-term exposure can not only benefit the tolerance study of aquatic organisms, but also have important significance on maintaining the sustainable development of water ecosystem.In this thesis, we studied the acute toxicity of ammonia nitrogen of larval mortality rate and the median lethal concentration. And based on the acute toxicity test and the water quality standard of five kinds of surface water, we investigated the the long-term stress of low concentration of ammonia nitrogen (0.5,2.0,4.5,9.0,18.0mg·L-1) on the juvenile grass carp (Ctenopharyngodon idellns) morphological and physiological characters, and analyzed the pattern of the juvenile grass carp response on the stress. The results were as follows:1.96h acute toxicity test of ammonia nitrogen stress on juvenile grass carp showed that the mortality of the juvenile grass carp increaseed with the rising of the ammonia nitrogen and the extension of time. The half lethal concentration of the24h,48h,72h and96h of ammonia nitrogen were85.47,66.61,57.43,48.16mg·L-respectively. The safe concentration of ammonia nitrogen was4.816mg·L-1.2. The research on the effects of the sublethal concentrations of ammonia nitrogen (0.5、2.0、4.5、9.0、18.0mg·L-1) of long-term stress on juvenile grass carp morphological and physiological characters showed that the physiological activities of juvenile grass carp suffered different effects under the ammonia nitrogen stress. However, the juvenile grass carp has self-defense ability of a certain degree to resist stress by themselves. By studying their physiological and biochemical responses under ammonia nitrogen stress, we could know more about the tolerability of juvenile grass carp to ammonia nitrogen.(1) At the concerntration of0.5mg·L-1, the body length and weight showed no obvious change compared with the control treatment.The content of MDA and ROS, the activity of antioxidant enzymes and antioxidants content in liver, gill, muscle tissue were all at the normal levels.0.5mg·L-1ammonia nitrogen treatment has no impact on juvenile grass carp. (2) When ammonia nitrogen concentration was2.0mg·L-1, the cell membrane system stability and antioxidant defense systems in gills tissue of juvenile grass carp were affected. The content of MDA and ROS of the juvenile grass carp gill tissue increased with the extension of time. And the activity of antioxidant enzymes and antioxidants content were also rised in order to remove excessive ROS accumulated in juvenile grass carp gill tissue. The juvenile grass carp kept the normal growth.(3) When ammonia nitrogen concentration was4.5mg·L-1, the body length, weight, the cell membrane system stability and antioxidant defense systems in livern gills tissue of juvenile grass carp were affected. The growth rate of body length and weight decreased compared with the control treatment. The content of MDA and ROS of the juvenile grass carp liver、gill tissue increased with the extension of time. And the activity of antioxidant enzymes and antioxidants content were also rised in order to remove excessive ROS accumulated in juvenile grass carp liver, gill tissue respectively. However, after38days recovery, MDA and ROS content, antioxidant enzyme activity and antioxidants content of the juvenile grass carp liver, gill tissue recovered, while the growth of juvenile grass carp remaned slow. The growth of juvenile grass carp were affected.(4) When ammonia nitrogen concentration was too higher (>9.0mg·L-1), the juvenile grass carp growed slowly after stress removal. The MDA and ROS levels of the juvenile Grass fish liver, gill, muscle tissue rose sharply. Although antioxidant enzyme activity and the antioxidant levels increased, the juvenile Grass fish failed to remove excessive ROS accumulated. After38days recovery, MDA and ROS content, antioxidant enzyme activity and antioxidants content of the juvenile grass carp liver, gill and muscle tissue were still significantly higher than normal. Cell membrane lipid peroxidation damage was serious. The juvenile grass carp liver, gill, muscle tissue may need more time to recover to normal level or damage of juvenile grass carp muscle tissue was irreversible.