1. Grease large shallow roasting pan. Rinse red snapper with running cold water; pat dry with paper towels. Sprinkle fish lightly inside and outside with salt; place fish in pan.
2. Make stuffing: Dice celery stalks and chop onion. In 2-quart saucepan over high heat, heat water to boiling; add celery and onion; heat to boiling. Reduce heat to low; cook 5 minutes or until celery and onion are tender. Drain, reserving liquid. Put onion and celery in large bowl. Into 1-cup measure, drain liquid from oysters; add enough celery liquid to make 1/2 cup. Coarsely chop oysters; add to celery and onion. Stir in bread cubes, butter or margarine, poultry seasoning, pepper, and oyster liquid.
3. With spoon, lightly fill fish cavity with oyster stuffing. Skewer fish cavity closed with toothpicks. Brush fish with salad oil.
4. Bake fish in 350°F. oven 1 hour 10 minutes, brushing fish occasionally with salad oil, until fish flakes easily when tested with fork. With 2 pancake turners, lift fish to warm platter. Remove toothpicks.
5. To serve, cut top side of fish into serving-sized portions just down to bone. Serve each portion of fish with some of the oyster stuffing. Lift off all bones and repeat with other side of fish.