| Four experiments were conducted in this study, experiment 1 was the field investigation and experiment 2-4 were observation for effects of the water-borne Cd on southern catfish (Silurus meridionalis Chen) under laboratory condition. In expeperiment 1, during October and November in 2013, totaling of 195 specimens for 7 siluriformes species were collected from the Luoqi section of the Yangtze River, the Fushun section of the Tuo River, the Beibei and Hechuan sections of the Jialing River. The Cd contents in every sample from the sections were detected and analyzed. In expeperiment 2, the mortality rate, hatching rate, hatching time of southern catfish embryos was examined after exposured to Cd, and the heart rate, survival rate, body malformations rate in newly hatched larvae was investigated after transferred to Cd-free fresh water 4days. In expeperiment 3, the tolerance degree of 1-and 10-days old larvae of southern catfish was examined throgh exposured to the water-borne Cd of acute toxicity experiment. In expeperiment 4, we examined the effects of Cadmium (Cd) on malondialdehyde(MDA) content, the total antioxidant capacity(T-AOC), metal lothionein(MT) content, hemoglobin (Hb) content and activity of acetylcholin esterase(AChE) in juvenile southern catfish, after exposure to the waterborne Cd for 0,7 and 14 days.The main results from experiment 1were follows:(1) Cd was detected in the every sample. The mean content of Cd in the samples of Luoqi section ranged from 0.023 to 0.175 mg/kg, it means part samples of the Luoqi section exceeded the limit value(0.1 mg/kg) of the national safety criteria for food in China (GB2762-2012). The mean content of Cd in the samples of Hechuan section ranged from 0.009 to 0.054 mg/kg, all the samples of Hechuan section not exceeded the national safety criteria for food in China. The mean content of Cd in the samples of Beibei section ranged from 0.073 to 0.162 mg/kg, part samples of the Beibei section exceeded the national safety criteria for food in China. The mean content of Cd in the samples of Fushun section ranged from 0.118 to 0.194 mg/kg, all the samples of Fushun section exceeded the national safety criteria for food in China.(2) The content of Cd in Pelteobagrus vachelli collected from all the sections was compared:Fushun section (0.194±0.029 mg/kg)> Beibei section(0.111±0.040 mg/kg)> Hechuan section (0.054±0.014 mg/kg)> Luoqi section (0.023±0.004 mg/kg). In addition the content of Cd in Pseudobagrus nitidus collected from all the sections was compared:Fushun section (0.164±0.012 mg/kg)> Beibei section(0.162±0.080 mg/kg)>Luoqi section(0.108± 0.069 mg/kg)> Hechuan section (0.017±0.002 mg/kg).(3) Regreesion analysis showed that there were significant positive correlation for Cd content and body length or body weight in the Silurusasotus of Fushun section(p<0.05).The main results from experiment 2 were follows:The median lethal concentration(LC50) for southern catfish embryos exposured to Cd after 48 hours was 49.34 mg/L and the maximum mortality of embryos occurred at the stage of gastrulation formation(exposured 8-20 h). Embryos exposured to Cd showed a significant increase in embryos mortality rate and body malformations rate of newly hatched larvae(p<0.05), while signicantly reduced in hatching rate and premature hatching(p<0.05), lead to flocculent egg membrane and agglutinate embryos. No significant difference was observed in larvae mortality rate(p>0.05) while the heart rate and body malformations rate were significantly increased(p<0.05), and the body malformations rate reached a peak at 48 h after transferred to Cd-free fresh water.The main results from experiment 3 were follows:Survival rates of 1-day old larvae had no significant difference among all the groups (p>0.05) after 24 h exposure, survival rates in the group of 0.64 mg/L were significantly lower than other groups (p<0.05) after 48 h exposured, survival rates in the groups of 0.16 mg/L,0.32 mg/L, and 0.64 mg/L were significantly lower than other groups (p<0.05) after 72 h and 96 h exposured. The median lethal concentration in 96 hours(96 hLC50) of 1-day old larvae was 0.104 mg/L, and the 10-day old larvae was 0.039 mg/L. Effects of Cadmium exposure on survival rate of larvae Show clear dose-response effect and time dependent effect.The main results from experiment 4 were follows:Hb content and AChE activity in brain decreased with increasing Cd2+at 7 days, the relationship between AChE activity and Cd 2+ could be describe as equation AChE=-0.395Cd+1.191, (n=30, R2=0.851, p<0.05), there was no significant difference about Hb content and AChE activity between Cd treatments and the control at 14 days. T-AOC and MT content in liver increased with increasing Cd2+ at 7 days, the relationship between MT content and Cd2+ could be describe as equation MT= 11.616Cd+13.738, (n=30, R2=0.754, p<0.05), and T-AOC level of liver in 0.96 mg/L group was significantly higher than the control(p<0.05), T-AOC progressively increased with increasing Cd2+ at 14 days, but MT content showed a downward trend after the rise. The hepatic MDA content in Cd treatments had no significant changes compared with the control (p<0.05) at 7 days, and it decreased with increasing Cd2+at 14 days.The conclusions suggested in this study were as follows:1. Siluriformes species from upstream of the Yangtze River and its branches were polluted by Cd in varying degrees, and the Fushun section of branch Tuo River was polluted more serious. It also suggested that bioaccumulation of Cd increased with body length or body weight in the Silurusasotus of Fushun section.2. The tolerance degree of southern catfish embryos exposure to Cd is relatively stonger than existing toxicity data for other test fish, and the maximum mortality of embryos occurred at the stage of gastrulation formation(exposured 8-20h). Exposures to Cd during embryonic period alone caused adverse impact on larval performance, even when larval development took place in clean water. Therefore, the effects of waterborne Cd pollution on southern catfish would consider toxicity data of pollution sources are removed.3. The larvae southern catfish was more sensitive to Cd exposure than most fishes reported in literatures,10-day old larvae was more sensitive to exposure of Cd than 1-day old larvae. The stage of 10-day larvae may be the bottleneck period of water-borne Cd, So the water quality protection work of southern catfish should key consider 10-day larval.4. The effects of Cd exposure on southern catfish was reflected in the AChE activity and Hb content at 7 days, however, southern catfish increased T-AOC and MT synthesis against cadmium poisoning. The effects of Cd exposure was reflected in the MDA decrease accompanied the significantly increase of T-AOC and MT synthesis, it was characterized by "hormesis". Southern catfish was able to adjust its physiological functions and reduce the damage caused by the certain concentrations of Cd pollution stress in environment. |
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