Effects Of Different Temperature On Mercury-induced Toxicology In Grass Carp(Ctenopharyngodon Idella)

Mercury, as a familiar heavy metal pollutant in our life, is considered to be a serious threat to the survival, development and reproduction of aquatic organisms. Temperature is an important abiotic ecological factor. Temperature can change the toxicity of heavy metal by varying their physicochemical property. The physiological and biochemical process of aquatic organisms also can be affected by temperature. Water temperature fluctuations often occur naturally or as a result of anthropogenic perturbations such as thermal pollution, deforestation and dam building. Water temperature changes can influence the property of mercury, and affect the toxicity on the aquatic organisms. The mechanisms of it are not clear and remain to be elucidated. In this study, grass carp(Ctenopharyngodon idella), an important economic fish of fresh water, was exposed to low concentration Hg2+(0.039mg/L, 10% of the 96 h median lethal concentration) in five different temperatures, each temperature has a control group. The test was long for 7, 14, and 28 days. The objectives of this study were focus on the effect of temperature on Hg2+ induced organizational structure, biochemical and demonstrated indices(morphomatric indicators, blood indicators,antioxidant indicators, energy metabolism parameters) and the expression of them. The main results of the experiments were as follows:1. Morphomatric indicators showed that: the condition factor(CF) of control group and mercury exposed group of 35℃ were significant reduction after 28 days, hepatosomatic indices(HSI) of all exposed groups and control group of 15℃ were showed significantly higher at 7 days, and the HSI of mercury exposed group of 15℃ decreased very significantly at 14, 28 days,compared with 25℃control group.2. Pathological section in liver of grass carp showed that the liver cells of 35℃ control group had vacuoles and necrosis after 28 days. The liver cells of all mercury exposed groups had phenomenon of demarcation line becoming fuzzy, cell nucleus concentration, deformity,necrosis, even disappear. 15℃ mercury exposed group the cell membrane damage was serious,cell was blurry and the nucleus necrosis in severe cases, 35℃ mercury exposed group the nucleus malformation and atrophy, particularly serious.3. For hematological parameters, the level of cortisol(COR) rise significantly in mercury exposed groups(30E and 35E)at higher temperature. The level of thyroid hormone T3 rised significantly in 25 E and 30 E groups at 7 days and 28 days, while significantly change of thyroid hormone T4 occurred in low temperature groups. Compared with the normal temperature group, the activities of antioxidant enzymes increased significantly in higher temperature mercury exposed groups after 14 days, while catalase(CAT) of all groups changed obviously before 14 days. In energy metabolism parameters, activities of Na+-K+-ATPase and pyruvate kinase(PK) were significantly increased in low temperature groups, and significantly inhibited in high temperature groups. The activities of hexokinase(HK) of mercury exposed groups decreased obviously. The activities of malate dehydrogenase(MDH) were significantly higher in lower temperature groups than control group. the protein level of metallothionein(MT) of all mercury exposed groups were significantly higher than control group at 28 days, except 35 E group.4. In all of groups, gene expression of antioxidant enzymes varied differently. The m RNA levels of superoxide dismutase(SOD) and Glutathione Reductase(GR) changed significantly at 14 days, while CAT and glutathione peroxidase(GPx) changed obviously at the beginning of the test. The gene expression of energy metabolism parameters were significant changes in lowest and highest temperature groups, while there was no obvious change in 30℃ group.5. In order to analyze the interaction effects between mercury and temperature, the two-way ANOVA was used. It showed obviously that some biochemical parameters were more sensitive to the temperature, including HK, SOD and MDH, However, the parameters such as Na+-K+-ATPase, PK, CAT and MDH were more sensitive to the mercury. While at the level of the gene expression of atp1b1a、hk1、mdh1b、pkma、gpx、mt、hsp70 were influenced by temperature significantly.