Mercury is often released into water bodies with industrial effluents, where it is then converted to the compound form methylmercury. methylmercury is easily absorbed by aquatic organisms. research suggests that the presence of mercury seriously decreases the reproductive rate of fish-eating birds, like heron, and causes other notable harmful effects. on the other hand, the small fish on which the herons prey are not significantly affected. explain why the toxic effects of mercury is significant in herons, but not in the fish they eat.