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The harmful effect of waterborne mercury (Hg) as a common biotic stressor to aquatic environment has gained much more interest nowadays. The current study aimed to investigate the impact of lethal and sub-lethal doses of mercuric chloride (HgCl2) on the embryonic development and dietary supplementation with selenium, vitamin C and vitamin E to mitigate its toxicity on the common carp (Cyprinus carpio) fish. Five hundred of newly hatched larvae were assigned into five groups for 60 days. The control (C) group and the other four groups were exposed to HgCl2 at doses of 0. 02, 0.04, 0.06, and 0.08mg/ l, respectively. Only the group exposed to HgCl2 at doses of 0.08mg/ l was fed on basal diet treated with selenium(2mg/ kg), vitamin C (3000IU/ kg), and vitamin E (100mg/ kg) for 20 days at the end of the experiment. The results revealed that the HgCl2 exposed embryo experienced abnormal lesions such as lack of tail and yolk sac edema. After exposure to HgCl2, the small larvae lost equilibrium, and their growth indices were retarded, resulting in an increased mortality rate. The morphological observation of the larvae under effects of HgCl2 were classified into axial lordosis, lateral scoliosis and curvature of the spine. Since the larvae ranged from 10 to 25 days in age, the heavy metal became more dangerous, and the mortalities rate increased. Histopathological alterations revealed that the gills in HgCl2 exposed group were more affected than the gills of the control and treated group. The gill lamellae revealed a decrease in heights and an increase in the thickness of the primary lamellae. Overall, selenium, vitamin C and vitamin E could be added to the diet of Cyprinus carpio larvae to alleviate stress condition caused by mercury.
Rania O. Barakat et al. (Wed,) studied this question.