Ecophysiological Effects Of The Water-borne Lead (Pb) Concentrations On Southern Catfish(Silurus Meridionalis)

The effects of acute and chronic toxicity of water-borne lead (Pb) with the water hardness25mg CaCO3/L on the juvenile southern catfish (Silurus meridionalis) of14.6-18.8g were observed at27.5℃. The median lethal concentration of southern catfish at96hours (96h LC50) was determined in the acute experiment. In chronic experiment of8weeks the effects of different Pb concentrations on the oxidative damage, growth performance, metabolic and tissue accumulation were measured in the tested fish at0,0.2and0.4mgPb/L, respectively.The main results from this study as follows:1. In the acute Pb exposure experiment, the mortality of the fish increased with increasing water-borne lead concentrations. The value of96h LC50was estimated as4.63mgPb/L by using the method of a straight line interpolation, and the safe concentration (SC) was calculated as0.463mgPb/L.2. During the8-week chronic exposure experiment, no mortality occurred in each of the tested group. The activities of GST, in liver, kidney and gill of the tested fish increased with increasing Pb concentration. The difference of the activities of GST in the liver between0.2and0.4mgPb/L treatment groups was not significant, but each of them was significantly higher than that of the control group (p<0.05), respectively. The difference of the activities of GST in the kidney between the control group and0.2mgPb/L group was not significant, nor was between the0.2and0.4mgPb/L groups. But the value in the0.4mgPb/L group was significantly higher than that in the control group (p<0.05). The difference of the activities of GST in the gill between0.2and0.4mgPb/L group was not significant, but the values in the both groups was significantly higher than that in the control group (p<0.05).3. The level of T-AOC in liver, kidney and gill increased with increasing Pb concentration, the levels in the three organs in either0.2and0.4mgPb/L group were significantly higher than those in the control group (p<0.05). The level of T-AOC in liver and kidney of the high Pb concentration group were significantly higher than the low Pb concentration group (p<0.05). But the values of gill tissue between in the two Pb concentrations groups were not significantly different.4. The contents of MDA in liver, kidney and gill increased with increasing Pb concentration, the contents of MDA in liver, kidney and gill between the groups at0.2and0.4mgPb/L treatments group was not significant, but they were significantly higher than the control group (p<0.05).5. The activities of TChE in brain decreased with increasing Pb concentration, the difference of the activities of TChE in brain between the groups at0.2and0.4mgPb/L treatments was not significant, but0.4mgPb/L group was significantly lower than that in the control group (p<0.05).6. The glycogen content decreased with increasing Pb concentration, the value in liver of0.4mgPb/L group was significantly lower than that of0.2mgPb/L group (p<0.05), and that in the either group was significantly lower than that in the control (p<0.05). But for muscle glycogen no significant differences were found among the three groups.7. The resting metabolic rate for the standard body weight increased with increasing Pb concentration. The difference of the resting metabolic rate between the groups at0.2and0.4mgPb/L was not significant, but the value in the either group was significantly higher than that in the control group (p<0.05).8. The specific growth rate decreased with increasing Pb concentration. The difference of specific growth rate between groups at0.2and0.4mgPb/L was not significant but they were significantly lower than that in the control group (p<0.05). The hepatosomatic index increased with increasing Pb concentration, and difference of the values between in the groups at the control group and0.2mgPb/L group was not significant, but they were significantly lower than0.4mgPb/L group (p<0.05). The condition factor and the feed efficiency were not significantly different among the three groups.9. The contents of lead in liver, kidney, gill, gut, stomach, muscle, carcass and whole fish increased with increasing Pb concentrations, and the contents of lead in the each tissue in the groups at either0.2or0.4mgPb/L group were significantly higher than the control group (p<0.05). The contents of lead in the each tissue at0.4mgPb/L were significantly higher than those at0.2mgPb/L treatment (p<0.05), except the gut and muscle. The contents of lead in organs could be ordered from higher to lower as following:gill> liver> kidney> carcass> whole fish> gut> stomach> muscle. The conclusions suggested in this study were as follows:1. Compared to the most fish species in the reported literatures, the96h LC5o with Pb exposure in the southern catfish was higher, which suggested that this have high tolerance to Pb toxicity.2. The activities of GST and the levels of T-AOC in liver, kidney and gill of the southern catfish increased with increasing Pb concentrations. The poisonous fish was able to adjust their antioxidant defense system and inhibit lipid peroxidation, reducing the damage to the fish.3. The glycogen content in liver decreased and the resting metabolic rate increased with increasing Pb concentrations, which suggested that the fish under stress of Pb exposure could adjust its metabolic mechanism to supply extra energy for the damage repair and poison cleanup process.4. The descend in growth of the fish with Pb exposure should result from less energy allocation to its growth.5. The content of lead was accumulated more in gill, liver, kidney and skeleton in the fish with Pb exposure, and that in muscle was minimum.