To make stock, bring shrimp shells to a boil in water (can also add carrot skins, celery leaves, fennel greens, and onion skins). Simmer for 2 hours. Drain and reserve liquid.
In large stockpot, add all vegetables, including garlic, and sweat until onions are translucent.
Add tomato puree, bay leaf, thyme, shrimp stock, chipotle pepper, and oregano. Simmer for 2 hours.
Add salmon and white fish. Simmer for 1 hour more, breaking fish with back of spoon. Add shrimp and clams. Cook 1 minute. When ready to serve, add black peppercorns and cilantro. Remove chipotle.