Additional Googling shows that saltwater catfish (as freshwater catfish) are scavengers. That would also exclude cod as their prey. Also, saltwater catfish in the Atlantic live in the south, are known as hardheads, and have very painful barbs, so I think if they were tightly packed with live cod, there would be injuries.
Also, hardheads live in shallow muddy water. This is not cod habitat, so this is another reason why catfish would not be their predators.