A broth made from fish bones, heads, and other trimmings, a good fish stock is the backbone of bouillabaisse, chowder, paella, and other classic dishes.
Fish stock is much quicker and easier to make at home than beef or chicken stock. It's made by gently simmering fish heads and bones with aromatic vegetables in water for about minutes. The heads are a rich source of gelatin, which contributes body to the stock, but if you don't have them you can make a fine stock with just bones. If you have any trimmings of fillets, they're a welcome addition, but don't add any gills or skin, which turns the stock gray and bitter.
The best bones for stock are those from fish with sweet, white flesh, such as flounder, sole, snapper, sea bass, or cod. Avoid bones from strongly flavored, oil-rich fish such as as salmon, bluefish, and mackerel.