Several times in recent years I've gotten 4-6 inch catfish, 50 per bag, and double bagged like ESSHUP mentioned. The bags were also in cardboard boxes. These have been from local suppliers within 45 minutes of the ponds. But, they made it without incident. Catfish any bigger than that require a hauling tank, or they will puncture the bags.
These photos are from four years ago, but they show how they get packed.
