Warm the oil in a large stock pot over medium heat. Add the sliced fennel, onion, garlic, salt, and chili flakes. Sauté for 10 minutes, stirring occasionally.
Add the stock, tomatoes, parsley, Worcestershire, thyme, oregano, allspice, and celery salt. Bring to a boil, then simmer for 2 minutes. Add the okra, cover, and cook for 8 minutes at a low boil.
Add the salmon chunks and scallops and let cook for 3 minutes (no need for mixture to boil again). Add the shrimp and cook for 2 minutes more. Remove from heat. Garnish with fennel fronds and serve immediately.