Expression of Hepatic Metallothionein in Guppy Fish (Poecilia reticulata) Exposed to Composite Tannery Wastewater

Throughout the year composite industrial and municipal wastewater contaminate the East Calcutta Wetlands (ECW; lat.22°33' - 22°40'N; long. 88°25' - 88°35'E), a special conservation site (Ramsar Site No.1208), in Kolkata city, West Bengal, India. Tannery wastewater is mainly characterized by high salinity, high organic loading and harmful heavy metals, especially chromium. However, the composite wastewater discharges are being productively utilized in the aquaculture after stabilization and also being used to irrigate adjoining farmlands. Industrial discharges in aquatic bodies may lead to increased concentrations of toxic chemicals and elements including heavy metals in the medium, which in turn affects the freshwater food-web. The liver is a vital organ that plays an important role in metabolic processes by the way of detoxifcation of xenobiotics. Present study was conducted to record the bioaccumulation of metals in a fish (Guppy; Poecilia reticulata) biosystem when exposed to composite tannery effuent. The 96-h LC₅₀ tests were conducted to measure the vulnerability of fish to composite tannery wastewater. The present study was also undertaken to determine the cell-types that exhibited metallothionein (MT) expression in liver tissue of guppy fish survived in sub-lethal dose of composite tannery effuent. It was evident from the study that metal concentration was higher in tannery effuent exposed fish in comparison to the unexposed fish (control fish where no tannery effuent was mixed). Immuno Electron microscopic study for the presence of metallothionein in treated fish along with the control specimen showed signifcant induction of fish hepatic MT under sub-lethal exposure to tannery effuent. Metalloprotein complexes sequester firmly the extra loads of metals in liver and thereby hinder the infuences of hazardous metals in fish biosystem. Hence, the induction of fish hepatic MTs could be conveniently employed as biomarkers for metal contamination.