Effects Of The Water-borne Cadmium (Cd)on The Oxidative Stress And Histology Of Gobiocypris Rarus

The oxidative stress and histology response of Gobiocypris rarus after exposure to the water-borne cadmium (Cd) was investigated in artificial soft water (35.72CaCO3mg/L) at (24.8±0.2)℃. Two series of experiments were conducted under the laboratory condition. The first experiment is about acute toxicity experiment of Cd exposure. According to the results of preliminary experiment, the Cd exposure concentration in acute toxicity experiment was set at0、2.50、2.86、3.26、3.72、4.23、4.83and5.50mg/L. The median lethal concentration in96hours (96h LC50) of Gobiocypris rarus was determined. The second experiment is subacute toxicity experiment of Cd exposure. Based on the result of96h LC50, the Cd exposure concentrations in subacute toxicity experiment was designed as0、5、15.27、45.83、137.5、412.5and1237.5μg/L. And then, the effects of different water-borne Cd concentrations on oxidative stress and histology of Gobiocypris rarus were studied. The main results were shown as follows.The results in the first experiment were shown as follows:The mortality of Gobiocypris rarus increased with increasing Cd concentration in the96-hour acute toxicity experiment. Through the method of probit regression analysis of SPSS, the median lethal concentration (2.75mg/L) of Cd to Gobiocypris rarus was obtained.The results in the second experiment were shown as follows:1. The effect of water-borne cadmium on the content of MDA in livers, gills and testes of Gobiocypris rarusThere was a significantly positive linear correlation between the malondialdehyde (MDA) content in the livers, gills and testes of Gobiocypris rarus and Cd exposure concentration in each group.2. The effect of water-borne cadmium on the total antioxidant capacity (T-AOC) in livers, gills and testes of Gobiocypris rarus There was a significantly positive linear correlation between the total antioxidant capacity (T-AOC) in the livers of Gobiocypris rarus and Cd exposure concentration in each group, but the T-AOC level in the gills and testes of Gobiocypris rarus showed a first increased and then decreased with Cd concentration increasing.3. The effect of water-borne cadmium on the SOD activity in livers, gills and testes of Gobiocypris rarusThe SOD activity in livers, gills and testes of Gobiocypris rarus all showed a first increased and then decreased with Cd concentration increasing, the highest SOD activity in livers and testes of Gobiocypris rarus appeared in412.5μg/L group, but the highest SOD activity in gills appeared in137.5μg/L group.4. The effect of water-borne cadmium on the CAT activity in livers,gills and testes of Gobiocypris rarusThe CAT activity variation trend in livers, gills and testes of Gobiocypris rarus was similar to SOD activity variation trend in that of Gobiocypris rarus of Cd exposure concentration. The highest CAT activity in livers of Gobiocypris rarus appeared in137.5μg/L group, but the highest CAT activity in gills and testes of Gobiocypris rarus appeared in45.83μg/L group and412.5μg/L group respectively5. The effect of water-borne cadmium on the AChE activity in the brain of Gobiocypris rarusAfter15days Cd exposure, the activity of acetylcholin esterase (AChE) in brain of the Gobiocypris rarus had a downward tendency with the Cd concentration increasing, AChE activity in the15.27、45.83、137.5、412.5、1237.5μg/L group was all significantly lower than control (p<0.05), and the inhibition ratio was61.50%in1237.5μg/L group.6. Effects of the water-borne cadmium (Cd) on the histology of Gobiocypris rarusThe liver histology of the control group appeared relatively normal. The normal structure of the liver, indicated by typical hepatic cord and hepatopancreatic structure.The nucleus is clearly visible in the center of the cell. Compared to the control group, various histological changes were identified in livers of fish exposed to Cd concentrations. These histological changes included hyalinization, hepatocyte cellular swelling, congestion of blood vessels, transfiguration of hepatocytes, eccentric position of nuclei, enucleation and development of vacuoles in cytoplasm. In addition, this study found these lesions change from the local to the overall diffusion rather than. The overall uniform lesions and the magnitude of changes did not increase in proportion to increased dose and time period. The gill histology of the control group appeared relatively normal. The gill filaments and lamellae showed normal morphological features. Note well-organized pavement cells. After exposure to Cd concentrations, the histopathological changes in the gill such as edema, epithelial necrosis, fusion of secondary lamellae, hemorrhage at filaments, hypertrophy of epithelial cells and sloughing off of epithelial surface are the major effects. The light microscope examination of the testis of Gobiocypris rarus had normal structure with evidence of well-organized distribution of cells in the seminiferous epithelium. With the increase of Cd2+concentration and duration of treatment, a series of pathological changes were observed including disordered arrangement of germ cells, decreased number of sperms in the lumina of the seminiferous tubules, The growth of spermatogonium are suppressed, testis-ova, etc. Histological studies revealed that the kidney sections from control fishes showed normal histoarchitecture. Kidney of fishes exposed to cadmium chloride for15days produced results of the loosening of haemopoietic tissue, uriniferous tubules having lost their original appearance, vacuolated cytoplasm. The cells constituting the wall of uriniferous tubules have become completely destroyed.The lumen of uriniferous tubules has become greatly shrunken and transfiguration.The main conclusions suggested in this study were shown as follows:1. Compared with fish toxicity classification standard and the majority of the fish in the reports and references, The water-borne Cd belongs to the category of high toxic heavy metal to the96h LC50of the gobiocypris rarus. This showed Cd has a higher poisonousness to the Gobiocypris rarus and the toxicity is associated with water hardness.2. Water-borne Cd concentration has a significant linear positive correlation with oxidative damage degree of the Gobiocypris rarus. It is suggested that content determination of MDA of the Gobiocypris rarus is considered as a biological indicator which is used as a biological monitoring of water metal pollution.3. The active reaction of AChE in brain of Gobiocypris rarus is very sensitive to exposure to Cd, it may be used as a biochemical criterion to show the degree of heavy metal poisoning of the brain indirectly.4. The testis of Gobiocypris rarus has obvious damage after exposure to Cd about the effects of Cd on oxidative stress and histology.5. Antioxidation mechanism in gills of Gobiocypris rarus has the first crash compared to other tissues, so the gills of Gobiocypris rarus are the most vulnerable organ.