3/4 cup vegetable oil, divided
1 cup medium diced onions
1 cup medium diced celery
1 cup medium diced carrots
2 quarts lobster, shrimp broth or fish stock
1 pound catfish pieces
1 pound shucked oysters (about 6 dozen oysters in shell)
3 tablespoons Cajun seasoning
1 pint grape tomatoes
3 bay leaves
Salt and freshly ground black pepper
1 cup all-purpose flour