Place fish in small plastic bags with less than 5 pounds of fish per bag. Then place the bags in a cooler and surround them with ice. Surround large, dressed fish with ice in a single bag, and put ice in the belly cavity. Drain the meltwater as necessary. Blood and bacteria drain from the fish into the melted ice, so avoid letting the fish lie in the meltwater.
Ice is the key to fresh tasting fish.
Note Fishing regulations prohibit mutilating fish in the field so that its size or species cannot be determined by officials. Consider leaving the tail, fins, and head on the fish until you get home. Cook or preserve the fish as soon as possible . Properly cleaned and iced fish keeps 4 to 5 days with little loss of eating quality and nutritional value. You're now ready to cook or preserve your fish.