Toxic Effects of Mercuric Chloride (HgCl2) on the Common Carp (Cyprinus carpio) Larvae and Recovery Using Selenium and Vitamins

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.