Heat butter and oil in a 6 to 7-quart stock pot over medium-high heat. Add onions, celery, pepper, and garlic and saute for 5 minutes, until softened and slightly caramelized. Add gumbo powder, bay leaf, cayenne, paprika, salt, thyme, oregano and pepper and continue cooking, another minute. Add tomato paste and cook until it browns, another 4 minutes. Add seafood stock, bring to a boil then reduce heat and simmer 30 minutes. Right before serving, add haddock and continue to simmer for 5 minutes, then add remaining seafood. Cook another 5 minutes. Add hot sauce, and season with salt and pepper, to taste. Serve over rice and sprinkle with file powder.