After an animal dies, some of its digestive enzymes erode the alimentary canal walls and invade the flesh. The flesh of an ungutted fish spoils faster under this assault than that of a land animal, partially because a fish's digestive enzymes are generally more efficacious. Remember, those biological catalysts that labor in the fish's digestive tract must chemically break down swallowed whole fish, bones and all. Compounding the disintegrating effect of the fish's potent digestive enzymes is the fact that fish flesh is easier to digest than terrestrial animal meat.

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