When I bought some sea bass at an East Asian supermarket in Los Angeles, I asked the vendor how he recommended preparing it. I picked up this habit in Paris, where the fishmonger often had interesting ideas. I expected him to tell me to grill this fine fish, but to my surprise, he said many people liked to use it in soup. Given the market's clientele, I pictured a seaweed-flavored Japanese soup with noodles, or perhaps one with Thai accents of lemongrass and fish sauce. But when I asked what he liked to put in the soup, he advised cooking onions with parsley and tomato sauce, and adding the fish. I then realized why he was giving me a Mediterranean-style recipe. He was Mexican, and he recommended making the soup the way he would at home, with flavors loved in Latin America as well. Cooks around the world know that making soup is one of the most economical ways to enjoy the fruits of the sea, as a relatively small amount of fish is needed for each portion. Flavors range from boldly-seasoned soups with lots of spice to delicate ones that highlight the fish's natural taste. When seafood soup is served to start off a meal, it might be a light broth with a few small cubes of fish and perhaps a hint of chives or parsley; or it might be a small bowl of rich creamy bisque or thick North American chowder flavored with milk and cream or with tomatoes. At Mexican seafood restaurants, I've also had chowder-like first-course fish soups, but they were lighter and spicier than their New England counterparts. Add vegetables to a seafood soup, and serve it with rice, noodles or hearty bread, and it becomes substantial enough to play the role of a main course. A mildly seasoned seafood soup that we savored at a Honduran restaurant owed its rich texture and luscious flavor to coconut milk; served with a generous mound of rice, it was a meal in a bowl. Coconut milk often enriches Thai seafood soup entrees, like a satisfying one I ate at a pan-Asian restaurant; it contained noodles, mushrooms and green onions, and was pungent from hot peppers and tangy from lime juice. An usual and very tasty central Vietnamese seafood curry soup that I sampled was embellished with quail eggs, peanuts, noodles, green onions, cilantro leaves and fried onions, and served with a large fried sesame cracker. There's nothing mysterious about making any of these seafood soups. People use ingredients with which they are familiar. I've even made a tasty fish soup supper by cooking cubes of salmon in a pot of vegetable soup. Most Westerners associate seafood soup with Mediterranean cuisine, which includes many fish soups in addition to the bouillabaisse of France and the ciuppin of Italy. Spanish, Greek, North African and Lebanese cooks all make fish soups matching the produce of the Mediterranean with the region's popular flavors - olive oil, garlic, onions, tomatoes and aromatic herbs. Because fish cooks rapidly, fish soups are easy to prepare and are ready in less time than most main-course soups. They're great for weight watchers, as they can be fairly low in fat. For a festive version, you can use a little oil to sautÃ© the vegetables and flavor the broth, but for an everyday soup, you can simply simmer the vegetables along with the fish. My favorite types of fish for soup are those that do not fall apart easily, such as sole, cod or halibut. But as long as the fish is fresh, even if it does not remain in neat chunks, the soup will still taste delicious. LEBANESE FISH SOUP WITH LINGUINE To give the soup a wonderful flavor, it is best to use homemade fish stock, but vegetable broth works as a substitute. Make the soup with or without tomatoes, according to your taste. Either leave the linguine whole or break it in short pieces. If you prefer rice to pasta, top each portion of soup with 3 or 4 spoonfuls of hot cooked rice. To get ahead, you can freeze the soup base. Then all you need to do is heat it and add the fish a few minutes before serving. 2 to 3 Tbsp. extra-virgin olive oil 2 large onions, halved, sliced thin a 400-gr. can tomatoes, drained, chopped, or 1â„2 cup tomato sauce (optional) 6 large garlic cloves, chopped 5 cups fish stock (see recipe below) or vegetable broth 1â„4 tsp. lightly crushed saffron threads, or 1â„4 tsp. turmeric Salt and freshly ground pepper to taste 100 gr. to 120 gr. linguine or very fine egg noodles for soup 450 gr. cod or halibut fillet, cut in 2-cm. dice 3 to 4 Tbsp. coarsely chopped basil, or 2 Tbsp. chopped fresh coriander or parsley Heat oil in a large wide casserole over medium-low heat. Add onions and cook for 10 minutes or until soft but not brown. Add tomatoes and garlic and heat for 1 minute. Add stock, saffron, salt and pepper. Bring to a boil. Cook uncovered over low heat for 20 minutes. Cook pasta uncovered in a large pan of boiling salted water over high heat until tender but firm to the bite; linguine needs about 8 minutes and fine soup noodles about 3 minutes. Drain well. Bring soup to simmer. Add fish and simmer uncovered for 5 minutes or until tender. Add linguine. If soup is too thick, stir in a little more stock or water. Add basil. Taste and adjust seasoning. Serve hot. Makes 4 main-course or 6 first-course servings. FISH STOCK To make stock, use heads, tails and bones of any fish - except strong-flavored ones like tuna and mackerel. If you're not using the stock within 2 days, freeze it. 400 to 500 gr. fish bones or heads 1 onion, coarsely chopped (optional) 1 large thyme sprig or 1 tsp. dried (optional) 1 bay leaf (optional) 6 cups water Rinse fish bones or heads thoroughly and put in a large saucepan. Add onion, thyme, bay leaf and water to cover. Bring to a boil; skim off foam. Simmer uncovered over low heat, skimming occasionally, for 15 to 20 minutes. Strain into a bowl. If not using right away, cool stock and refrigerate it. Makes 41â„2 to 5 cups. Faye Levy's latest book is Healthy Cooking for the Jewish Home, published this month by Morrow.