Soak the catfish fillets in the milk for about 30 minutes in the refrigerator.

Light a charcoal barbecue or heat a gas grill.

Shake off the excess milk from the fish and discard the milk. Pat the fillets dry.

Combine the crushed saltines with the seasoned salt, celery salt, black pepper and garlic. Dip the fillets first in the melted butter, then press them gently into the melted margarine.

Grill the fish over medium heat, covered, for about 10 minutes, turning once, until the fish flakes easily with a fork. You can also lay the fillets on a piece of strong aluminum foil and lay the foil directly on the grill.