In a large stockpot, steam the clams or mussels in one cup red or white wine until they open. Discard any that don’t, and remove the meat from the shells.
Set clams or mussels aside and strain wine broth through a fine cloth or mesh sieve and reserve. Heat olive oil in a large pot, and add onion, garlic, pepper, and mushrooms. Cook 3 minutes, then add tomatoes. Cook the mixture for four minutes. Add the reserved broth, tomato paste, and red wine. Season to taste with salt and pepper. Simmer for 20 minutes, and taste again for seasoning.
Add the sea bass. Cook just until done, then add the clams or mussels, crabmeat, and shrimp. Simmer just until the shrimp are cooked. Sprinkle with parsley and serve with crusty French or Italian bread.