However, eating deep-fried fish dipped in tartar sauce is not going to get you into nutrition heaven. The good news is, both of these complaints apply to old and improperly cooked fish, and both of these fish flaws can and should be avoided. Unfortunately, that's the kind of fish that many people have encountered. If you've never had really fresh fish, you've never really had fish. A proper piece of fresh fish should smell sweet and briny, like the ocean.
Fish is highly perishable, and it is delicate.
It should really be cooked the day you buy it, but it can be stored for a day or two as long as you keep it very, very cold. Since fish is so delicate, it dries out quickly and is also very easy to overcook. Overcooked fish is chewy and just doesn't taste as good. Perfectly cooked fish should flake easily but shouldn't completely fall apart when you pick it up with a spatula. Ideally, it should be opaque almost all the way through, with just the faintest amount of translucency in the middle.