Toxic effects of Zinc on gill and liver of Silver carp (Hypophthalmichtys molitrix)

One of the toxic pollutants in aquatic ecosystem is heavy metals. This study aims to elucidate the toxic impact of zinc on the structure of gill and liver in silver carp (Hypophthalmichthys molitrix). This study was conducted at spring 1390 at the International Sturgeon Research Institute. In this study, after adaptation, 135 fish with the length of 13±1 cm and the weight of 50±10gr were put in one control group and 2 treatment groups contained 0, 5, and 10mg/L (Zn (NO) 3)2 in 90 liter aquariums. Fish were sampled at 12, 24, 48, 72 and 96 hours. The samples of gill and liver in each treatment were immediately fixed in Bouin solution and 5μ sections were stained by Hematoxylin-Eosin general staining method. In histological study of gills, epithelial cell hyperplasia was encountered, that had increased with high metal densities. Initially lamella cells wrinkled and change of formation was observed in chloride cells. This lesion enhanced in higher densities. Fish liver exposed to zinc showed atrophy,cloudiness, swelling, hyperemia, vacuolation and necrosis. These hepatic alterations were more evident in fish exposed to high metal densities. In conclusion, the present study showed that histopathology of liver and gill in silver carp, is a useful biomarker for environmental pollution, since it discriminated between reference and test sites.