Yeah I’ve heard of people precatching fish and using holding containers.
That one’s been around for a long time.
Harder to do in saltwater tournaments.....the ones I’ve been in really are under the honor system.
Carl Hiaason wrote an hysterical book about cheating in bass tourneys: Double Whammy. The cheaters caught the fish a day or two before the tournaments and kept them on stringers or in fish baskets hidden in remote areas. It was very entertaining reading.