Seafood stock is one of those things I just can't deal with in a can; fresh is so far superior. If you happen to have some shrimp, crab or lobster shells, the process is actually pretty easy. A fish stock using whole fish heads can be a bit messier, so I'm going to recommend you go the shellfish route. This stock is a great base for soups and stews and for cooking risotto. Cook it down as a base for pasta sauces and sauces to top other seafood dishes.
Shellfish Stock makes about 2 quarts
5 cups shrimp heads and shells (from about 1 1/2 pounds whole shrimp) or crushed shells from crab or lobster 2 tablespoons olive oil 2 cups chopped onion 1 cup chopped celery ribs 1 cup chopped unpeeled carrots 4 garlic cloves, peeled and crushed 5 springs fresh thyme 5 Italian parsley stems 2 dried bay leaves 1 tablespoon whole black peppercorns 1/4 cup tomato paste 1/2 cup dry white wine 2 quarts boiling water Salt
Rinse the shrimp heads and shells in cold water and drain.
Heat the olive oil in a stockpot over medium heat. Add the onions, celery, carrots, garlic, thyme, parsley, bay leaves, and peppercorns, and cook, stirring occasionally, until the onions are translucent and the other vegetables soften, about 8 minutes.
Add the shrimp heads and shells, stir, and let the mixture sizzle for a few seconds. Add the tomato paste and wine. Stir once, cover, and cook for about a minute, shaking the pot once or twice.
Carefully pour in the water and bring mixture to a boil, then lower the heat and simmer, uncovered, skimming the surface and discarding any foam that builds up. Simmer over low heat for 45 minutes to an hour, checking for a deep color and rich seafood flavor. Add salt if needed toward the end of cooking.
Cool in an ice-bath and refrigerate or freeze if not using immediately.