During the season that I worked at the state hatchery, one task that I dreaded was loading the broodstock into the truck to be stocked.
Those fish weren't all that excited about being netted out of the raceways. During the chaos you'd get soaked, even in waders and rain gear, and then there was the matter of lifting them up to the tank. They're not exactly light weight.
I suppose at some time there would be a point where fins could be clipped to ID them. Maybe when they were being 'milked' for their biological product. But during the stocking process any time out of the water counted against their survival.
When we were out stocking I'd take mental notes of where they went (the sort of info that I took the job for in the first place ). Unfortunately, the 'thrill' of catching one was greatly diminished by the knowledge that despite their size, they were no different than any other average stocker.