author(s)
Pawan Kumar Joshi, Ashutosh Mishra and AP Sharma

abstract
An experiment was conducted in Lake Nainital from September, 2016 to February, 2017 to assess the extent of bioaccumulation of heavy metals from aquatic ecosystem to fish (Tor putitora). For this, three essential (Zn, Cu, Mn) and two non- essential (Pb and Cd) heavy metals were selected to analyze their concentration in water and fish (gills and muscles). Along with heavy metals, important water quality parameters viz. water temperature, electrical conductivity, total dissolved solids, dissolved oxygen, free CO₂, pH, total alkalinity and total hardness were also analyzed. The concentration of Zn, Pb, Cu, Mn and Cd in water varied from 0.013 to 0.051 mg L^-1, 0.137 to 0.629 mg L^-1, 0.00 to 0.263 mg L^-1, 0.00 to 1.314 mg L^-1 and 0.00 to 0.012 mg L^-1, respectively. The accumulation trend of these heavy metals was studied in gills and muscles of selected fish. The results shows that zinc (2.233 mg L^-1 ) and copper (0.051 mg L^-1) were accumulated with highest and lowest level, respectively in gills and accumulation trend of heavy metals followed the order of Zn>Pb>Mn>Cd>Cu while manganese (0.423 mg L^-1) and cadmium (0.00 mg L^-1) were accumulated with highest and lowest level, respectively in muscle of the fish and accumulation trend followed the order of Mn>Zn>Pb>Cu>Cd. To reveal the extent of accumulation of heavy metals in fish, bioaccumulation factor was employed and its values reflected that gills of selected fish serve as hyper- accumulator for Zn, Mn and Cd, whereas muscles are hyper-accumulator for Zn and Mn. The study concludes that the presence of elevated levels of Zn, Mn and Cd in fish can result in imbalancing the food web in the lake.