Immunolocalization of metallothionein in hepatocytes of guppy fish (Poecilia reticulata) exposed to tannery effluent: A biomarker study

- We examine the ecotoxicity of composite tannery effluent on fish biosystem.
- Bioaccumulation of metals in fish body upon exposure to tannery effluent.
- Significant induction of hepatic MT in treated guppy fish over control specimens.
- Induction and localization of MT may be considered as an important biomarker.
- Metalloprotein complexes in fish tissue sequestered excess load of metals.

Composite tannery effluent (TE) contaminated with a load of metals, especially chromium, is used in East Calcutta Wetland Ecosystem (ECW; a Ramsar site of West Bengal; No 1208) after natural stabilization for pisciculture and agriculture. Quantity and synergistic and antagonistic activities of both essential and nonessential metals in the effluents can induce a variety of complex changes in animal physiology. High fish yield and no apparent adverse influence on the fish biosystems thriving under pollutant stress at ECW allowed the practice to thrive sustainably over the last nearly 100 years. Thus, the present study was conducted to investigate the role of metallothionein (MT) as a potential biomarker in a fish biosystem following acute and chronic exposure to sublethal concentrations of tannery wastewater. MT localization in the liver tissue of guppy fish (Poecilia reticulata) was studied by the immuno gold-labeled electron microscopic technique. The data demonstrated increased metal content in fish body upon exposure to TE. Electron micrographs showed significant induction of hepatic MT in exposed P. reticulata over control specimens. Liver, being the detoxification site of an organism, plays a crucial role in the synthesis of MT and arrest of excess metal. The method employed in the present study for demonstrating the induction and localization of MT is innovative and could be used as a biomarker in fish exposed to metal stress. Our study also indicated that the metalloprotein complexes in fish tissue sequestered excess load of metals and thereby arrested unwanted interferences of excess metal loads in metabolic processes.