All fish species fall into two basic categories: round and flat. Ranging from massive swordfish to tiny sardines, round fish have torpedo-shaped bodies. Flatfish, such as sole and halibut, are bottom dwellers with flat bodies. Larger fish are broken down into smaller cuts, each of which is good for particular types of cooking. Cuts should be clean-smelling and firm, with tight-knit, even-colored flesh that hugs the bone. Avoid cuts that are spongy or falling apart, have a fishy smell, or show signs of yellowing or browning.