Fish 

Levels of pesticides and mercury need to be checked in the water from where the fish is drawn . Some species of fish may contain significant levels of methymercury, polychlorinated biphenyls (PCB's), dioxins, & other environmental contaminants. These substances are present in low levels infresh water & oceans, & they biconcentrate in the aquatic food chain such that levels are generally highest in older, larger, predatory fish & marine mammals. Consumers can reduce their exposure to PCB's by removing the skin & fat from these fishes before cooking them. however because methylmercury is distributed throughout the muscle, skinning & trimming does not significantly reduce mercury concentrations in fillets.
As far as possible, consume fish the same day, it is bought. If good refrigeration with good temperature control is available then it can be stored for 1-2 daysFollowing are some points which should be inculcated in day-to-day life.

• While buying meat/fish/poultry make sure they are freshly cut.
• Clean fish/ poultry/meat thoroughly before cooking. Cook them thoroughly before consuming.