Peel shrimp before cooking & devein. Make a roux... use oil and flour in a heavy iron skillet. Over medium-low heat, place flour in the oil and let cook , slow , until the flour starts to brown. Adjust heat so that the flour does not burn. You want the flour to turn dark brown, stir as needed but, keep dat flour from burning. When you are satisfied that the roux is as dark as possible without burning, add the cleaned shrimp to it for a few minutes, stiring constantly. Set the shrimp/roux mixture aside. Smother okra in another 2 T of oil, along with the chopped onions. Add can of tomatoes when the okra is nearly cooked. Then add water, bay leaf, garlic, salt and pepper. Add shrimp and roux to this mixture and let cook slowly for 20-30 minutes. Add oysters and crabmeat, cook for another 10-15 minutes. NOTE: If ya don't use okra, you can use gumbo file', which is crushed sassafras leaves, available in the spices rack of the grocery store. When using file' instead of okra, add it only after the heat is off... don't simmer or boil file'... it gets stringy. Let gumbo stand a few minutes after adding file' before serving. Serve over cooked rice.