Over medium heat melt 1 Tbsp of butter and 1 Tbsp of oil in a 12in non-stick skillet. Season both sides of fish fillets with seasoning and red pepper. Place 4 fillets in skillet and cook about 3-5 min per side until golden brown.
Repeat with another 1 Tbsp butter, 1 Tbsp oil, and remaining 4 fish. While fish is cooking, dice onion, green pepper, and celery. Mince garlic.
Once all fish is cooked, cover with a piece of aluminum foil to keep warm. Add remaining butter, oil, onion, bell pepper, and celery. Cook for about 3min and move to edges of skillet. Add mushrooms and garlic to center of skillet, cook about 2-3 minute.
Add broth, milk, shrimp and diced crab meat. Increase heat to medium high. Once it begins to boil, gradually add flour while constantly stirring to remove lumps. (Taste and adjust seasoning to your liking.) Serve over fish and possibly rice.
*I also added more seasoning and pepper to sauce. I really enjoyed it!