Fresh fish begins to develop an unpleasant fishy odor as it sits for a long time. Fish smells fishy. Simply put, it’s because the flesh begins to spoil, but do you know the details? To avoid a fishy smell when cooking fish, learn why.

Why does fish smell fishy?

This may sound like a silly question, but it has several interesting answers. People often tolerate fishy odors in markets and restaurants because they think, what else could it smell like? But fish doesn’t have to smell like fish at all—if it’s truly fresh.

If fish and shellfish have been out of water for just two hours, they have almost no odor. They might have a fresh “sea smell,” but it’s not unpleasant at all. That fishy odor only develops when seafood begins to spoil, and fish spoils much more quickly than other meats.

Reason 1: The fishy odor is a product of spoilage.

Fish (the muscle) is made of protein, but it’s a different type of protein than beef or chicken. Not only does it break down faster during cooking, but it also breaks down even more quickly under the attack of enzymes and bacteria.

In other words, it spoils faster. That fishy smell comes from the products of decay, particularly ammonia, various sulfur compounds, and chemicals called amines produced by the breakdown of amino acids.

The human nose is highly sensitive to these chemicals. We detect the odor long before the fish becomes unhealthy and uneatable. So a slight fishy odor simply indicates that the fish is not entirely fresh or flavorful, but not necessarily dangerous.

Amines and ammonia are bases that are neutralized by acids. This is why lemon slices, which contain citric acid, are often served with fish. The most accurate way to test the freshness of seafood is to politely ask to smell it before purchasing. However, in some Mediterranean markets with high standards, this can be considered a serious insult.

Reason 2: Enzymes Escape from the Gut

The second reason fish spoil faster than other meats is that most fish have an unfriendly habit of preying on smaller ones in the wild (it’s a jungle beneath the surface). Therefore, they possess digestive enzymes that are extremely effective at digesting fish.

After being caught, if rough handling causes certain enzymes to escape from the gut, they can quickly act on the fish itself. This is why gutted fish can last longer than whole fish.

Reason 3: Fish’s spoilage bacteria are more potent than those found on land.

The third reason is that the spoilage bacteria in and on fish are more potent than those found on land. This is because they are designed to thrive in the cold ocean, so even a slight increase in temperature makes them more aggressive. To prevent their nasty work, fish must be frozen more quickly and thoroughly than when preserving the meat of warm-blooded animals.

That’s why ice is a favorite of fishermen (lots of it). It not only lowers the temperature but also prevents the fish from drying out. Even after death, fish don’t like to dry out.

Reason 4: Fat Oxidation

Fourth, fish generally contain more unsaturated fats than land meat, which is one reason we treasure them in this age of cholesterol panic. But unsaturated fats turn rancid (oxidize) more quickly than the delicious saturated fats in beef. Fat oxidation turns them into foul-smelling organic acids, which further contribute to the unpleasant odor.

If you walk into a seafood restaurant that smells strongly of fish—leave immediately and find the nearest burger joint.

If your scallops smell even slightly fishy, ​​try rinsing them with lemon juice or vinegar before cooking. But don’t soak them, as they absorb water like a sponge; if you try to grill or pan-fry them, they’ll end up steamed.