Effect Of Chromium On Oxidative Damage And Antioxidant Capacity Of Ctenopharyngodon Idellus

This study aimed to investigate the effect of water-borne chromium on oxidative damage and antioxidant capacity of grass carp, Ctenopharyngodon idellus. Firstly, the median lethal concentration of grass carp in96hours (96h LC50) was determined in the preliminary experiment. Then, based on the result of96h LC50, the Cr6+exposure concentrations in acute toxicity experiment was designed as0,7.23,14.47and28.94mg/L. Lastly, the content of malondialdehyde(MDA) and total antioxidative capacity(T-AOC) in the hepatopancreas, gill and kidney of grass carp were determined after24,48,72and96hours in different treatment groups, respectively. At the same time, measured the catalase activities (CAT) of the hepatopancreas and gill, as well as the activity of glutathione S-transferase (GST) in the hepatopancreas. This study preliminarily investigated the possible oxidative damages caused by Cr6+exposure to grass carp as well as the antioxidant capacity and mechanism of grass carp, with the aim to provide certain references for the environmental protection departments to develop the effluent standards and protective measures as well as the quality control of aquaculture water.The main results from this study as follows:1. In the preliminary experiment, the mortality of grass carp increased significantly with the increase of the concentration of hexavalent chromium, the measured values of96h LC50and safe concentration (SC) to grass carp was57.88and5.79mg/L, respectively.2. Effect of chromium on oxidative damage and antioxidant capacity in the hepatopancreas of grass carp(1) From concentration-effect relationship to see, the MDA contents in the hepatopancreas of grass carp in each group were continuously increased. On the24hours, the MDA contents in all the experiment groups increased with increasing Cr6+concentrations, but no significantly higher compared to the control group (p＞0.05). On the48,72and96hours, the contents of MDA in all the experiment groups increased with increasing Cr6+concentrations, and were significantly higher than those in the control group (p<0.05). From time-effect relationship to see, the contents of MDA in the hepatopancreas of grass carp in each group were continuously increased. On the72and96hours, the MDA contents in the group of14.47and28.94mg/L were significantly higher than in the24hours group.It was suggested that the water-borne Cr6+exposure could significantly induce the large amout of active oxygen and the higher degree of lipid peroxidation, with the more increased concentrations and the longer exposure time.(2) From concentration-effect relationship to see, on the24hours, the T-AOC in the hepatopancreas of grass carp had no significantly changes compared to the control group (p>0.05). On the48and72hours, the level of T-AOC in all the experiment groups increased with increasing Cr6+exposure concentrations. In addition, the level of T-AOC in14.47and28.94mg/L groups on the48hours and in28.94mg/L groups on the72hours were both significantly higher than those in the control group (p<0.05). On the96hours, with the increasing of Cr6+exposure concentrations, the changes of T-AOC level first increased, and then decreased. When exposure concentration is7.23mg/L, the level of T-AOC is induced significantly, and then weakened with further increasing Cr6+exposure concentrations. From time-effect relationship to see, when the exposure Cr6+concentrations was7.23mg/L, the level of T-AOC were significantly higher on the96hours. The changes of T-AOC in the group of14.47and28.94mg/L firstly increased, both reaching the highest level on the48hours, and then decreased with the extending of time.(3) The general tendency of CAT and GST activities in the hepatopancreas of grass carp was as follows:On the24and48hours, the CAT and GST activities were induced in different degrees, On the72and96hours, the activity of CAT and GST was induced firstly and then had a tendency to decrease. In the acute exposure experiment, the CAT and GST activities were induced firstly and then decreased, except that the activity of GST in7.23mg/L group induced in different degrees and the CAT activities in28.94mg/L group weakly induced or even inhibited, compared to the control group. In addition, the responding sensitive degree of GST and CAT in the hepatopancreas of grass carp was different to chromium stress. On the72and96hours, the activity of GST was significantly induced in7.23mg/L group, and then inhibited with the increasing concentrations, while the activity of CAT had no significant change at the same concentration. It is suggested that the GST in the hepatopancreas of grass carp had a higher sensitivity than CAT in all chromium exposure groups.3. Effect of chromium on oxidative damage and antioxidant capacity in the gill of grass carp On the24hours, the MDA content and T-AOC level in the gill of grass carp gradually increased with the Cr6+exposure concentrations increasing, and then the content of MDA further increased, however, the level of T-AOC appear to be significantly induced and then had a tendency to decrease. With the extending of time, the MDA contents in the gill of grass carp in each group were continuously increased and the level of T-AOC in higher concentration groups (14.47and28.94mg/L) firstly increased, and then decreased. The activity of CAT in the gill of grass carp gradually increased with the Cr6+exposure concentrations increasing. With the extending of time, the CAT activities in each group were continuously increased and then decreased. Reaching the greatest activities on the72hours, the CAT activity was significantly decreased in the tested fish (p<0.05).4. Effect of chromium on oxidative damage and antioxidant capacity in the kidney of grass carpThe contents of MDA in all groups during the acute exposure experiment, and the level of T-AOC in kidney of grass carp at24and48hours in kidney of grass carp increased with increasing Cr6+exposure concentrations. Moreover, the T-AOC was induced firstly and then had a tendency to decreased on the72and96hours.5. Comparison of oxidative damage and antioxidant capacity of chromium exposure on the hepatopancreas, gill and kidney of grass carpWe found that chromium exposure could induce oxidative damage on the three kinds of tissue in grass carp. The order of the degree to oxidative damage were kidney> hepatopancreas> gill, and the level of total antioxidant capacity was opposite.Above studies have shown that grass carp on chromium toxicity tolerance is relatively high. Chromium exposure can cause different levels of oxidative damage in hepatopancreas, gill and kidney tissues of grass carp, and then The total antioxidative capacity including CAT, GST and so on occurred different degrees of influence,which suggested that effect of chromium exposure on oxidative stressof grass carp have some tissue specificity. Low concentration, short time of chromium exposure can not cause significantly oxidative damage and antioxidant levels slightly increased. With the increasing exposure concentrations and prolonging the time, Chromium exposure could significantly increased oxidative damage and showed obviously a concentrations-time effect as well as a time-effect relationships. Reaching the highest levels, the T-AOC had a tendency to decrease even inhibited, which indicated that the capacity of grass carp to chromium exposure is limited, and the balance between the oxidation and antioxidant could be broken in the body.