Impact of metals on histopathology and expression of HSP 70 in different tissues of Milk fish (Chanos chanos) of Kaattuppalli Island, South East Coast, India

Histological and Immunohistochemical studies were carried out to document the possible impact of heavy metal contamination in different tissues of Chanos chanos. Heavy metals such as Cu, Pb, Zn, Cd, Mn and Fe were predominant in water, sediment and biota of Kaattuppalli Island and varied significantly between two different sites. Histological changes such as swelling of muscle fiber and break down of muscle bundles were noted in the muscle. Similarly gill filament cell proliferation, increase in intercellular spaces and primary and secondary lamellar epithelium were evident in gills. The hepatocytes showed damage of central vein and rupture of irregular hepatic plate with more number of vacuoles in the fish collected from polluted site compared to that from the less polluted site. The impact of pollution was also assessed in different tissues by immunohistochemistry using primary antibody (mouse monoclonal HSP70 antibody 1:2000) and secondary antibody (HRP conjugated antibody) for expression of stress protein. Immunostaining analysis showed expression of HSP70 with high intensity in the tissues of fish collected from polluted site compared to less polluted sites. Further, HSP70 positive cells were analyzed from six locations per fish tissue section. One-way analysis of variance (ANOVA) followed by least significant difference (LSD) was used to check if the expression was significant. Results indicate that the values are statistically significant at the two different sampling sites (P < 0.05).

Research highlights
► Heavy metal accumulation in the water as well as in sediment sample was high in polluted sites.
► Accumulation of heavy metals Zn, Cd & Fe were high in all fish tissues collected from polluted sites.
► Histopathological damage and structural changes were evident in Chanos chanos by especially with metals.
► The expression of HSP70 was also high in gill and liver of fish collected from polluted sites.