Fish smell strongly because of amino acids in their secretions and tissues, which is rich in sulfur and very unstable once the fish dies. The amino acids break down quickly into volatile amines like ethylamine, which conveys a strong odor.

When you get fish slime on your hands, it begins to decay almost immediately. That’s when you smell ethylamine. Your nose is keen to pick up these unpleasant amines and it typically means that something is spoiled and unfit to eat.