Fillets

By far the most popular cut of finfish. Though fillets vary wildly in quality, many can be substituted for one another. Thin fillets, mostly cut from flatfish like flounder and sole, are almost all interchangeable; they’re tender, mild, and cook quickly. Thicker fillets have more variety of flavors and texture: red snapper and grouper, for example, are meaty, whereas cod has a fine, tender texture. Dark fillets, like mackerel, are oilier and more heavily flavored. (Then there’s salmon ...) But in general, it’s safe to say this: if two fillets look the same, they may be treated the same; if you go to the market looking for nice white sole and you find nice white flounder, go for it.