Combination of both I would think, something that I am seeing more and more of is the gripping/squeezing of Barbel around the vent area when a photograph is being taken could possibly produce the same sort of damage, what it does show is how careful anglers need to be with their fish.
Definitely looked like that fish was being held deliberately tightly and for way longer than necessary. Still worrying but not entirely convincing. I try to handle my fish as little as possible and get em back in the water as soon as.
I agree that it seemed to be held for a long time and very hard but it shows what can happen in extreme circumstances.
In the absence of any other such evidence, the damage will still happen to a lesser degree... it does show us that we need to take more care, even if we thought we were doing everything we could.
I've known all sorts of anglers squeeze their fish to make their fins go up for a photo.. carp, perch, zander, bass. Sad really that people even think it's okay. The way that some people hold perch with a horizontal lip hold and unsupported body is downright cruel imho.
Found this a while back and although it relates to US bass, perch have a similar mouth structure.
Never ever used a glove, not even for pike when I was younger or indeed the horrible snotties though why they have an excess slime coating is beyond me... probably a defensive strategy against anglers catching em! mg:
still working on that bream deterrent, should make a few bob :wh