No one likes overly fishy fish. The trouble is, unless you're cooking fish right after it was caught, it's likely to have been out of water for several hours—even overnight or longer. If it's been flash-frozen, that may not be a problem, but as fish lingers, even refrigerated, its aroma can become steadily more pronounced, even before it starts to go bad.
All of this is explained in greater detail in the recently published, very technical book from Cook's Illustrated, Cook's Science, so if you want to get down to the nitty gritty of the acids and bacteria in play that cause the odiferous reaction, check it out. What's more important, however, is that although fish and shellfish that's been sitting around for a little while may not be the most pleasingly fragrant, that doesn't necessarily mean it's gone bad. To determine if fish is still good to eat, trust your senses—there's a difference between a slight fishy smell and an acrid fish-gone-bad smell. Also, the flesh should be firm, not mushy, and should look and feel dewy as opposed to dried-out, or turning grey.
Once the fish is cooked and paired with a flavorful sauce, you might not even notice the smell anymore. But, if you want to make sure to get rid of the odor, Cook's Science does offer two easy solutions:
1. Before cooking, soak the fish in milk for 20 minutes
In this scenario, the protein in the milk binds with the compounds that cause that fishy odor, in essence extracting if from the fish. What's left behind is sweet-smelling, brighter flesh with clean flavor. (Just make sure you pour that milk down the drain. 'Cause ew.)
2. Squeeze lemon juice over the fish before cooking it.
Lemon juice will neutralize those odors, but it will also leave the fish with a citrusy flavor. But is that ever a bad thing?
