ABSORPTION AND BIOACCUMULATION OF WATER-BORNE INORGANIC MERCURY IN THE FINGERLINGS OF GRASS CARP, CTENOPHARYNGODON IDELLA

A study was conducted to evaluate the absorption and accumulation of total mercury (Hg) in various tissues of fingerlings of grass carp, Ctenopharyngodon idella when exposed to lower doses of water-borne Hg. Single breed fingerlings (10-12 cm) of grass carp were obtained from a commercial fish seed hatchery. Six groups (in triplicate) of fish (40 each) were maintained at 22 degrees C, pH 7.0, hardness 140 mg/l and DO 7.0 mg/l in 90 liters of water in glass tanks. Each group was exposed to a sub-lethal dose of inorganic Hg as 0.0 mu g/l (control), 0.1 mu g/l, 1.0 mu g/l, 2.0 mu g/l, 2.5 mu g/l and 3.0 mu g/l for six weeks. Fish sampling was done on day zero and weekly thereafter. Five fish from each tank (15/treatment) were sacrificed; various tissues were collected and prepared for analysis of total mercury using cold-vapor atomic absorption spectrophotometry. Fish tissues that were directly exposed to Hg, the absorption and accumulation was significantly high (P<0.05) in skin (including mucus) (1.68 +/- 0.012. mu g/g dry wt.), gills (1.64 +/- 0.013. mu g/g dry wt.) and eyes (1.45 +/- 0.011 mu g/g dry wt.) as compared to the tissues from control group. While the tissues that were not directly in contact with water containing Hg had accumulated it significantly high (P<0.05) in muscles (2.03 +/- 0.012 mu g/g dry wt.), intestine (1.39 +/- 0.015 mu/g dry wt.) and liver (1.38 +/- 0.013 mu g/g dry wt.) as compared to tissues from zero treatment. This study clearly indicates that the fishes living in water bodies receiving industrial effluents and city waste water containing various toxicants particularly heavy metal ions, even at low concentration, absorb and accumulate these heavy metals in their various tissues like skin (including mucus), gills and intestine directly from water as well as alongwith the food during feeding. With the passage of time as the fishes grow, these metals accumulate in various internal organs like liver, muscles and intestine to a significantly high concentration not suitable for human consumption.