It's a spawning thing but just seems excessive. I've seen that hump on large brook trout although as we all know the kype isn't that extreme on a large male brook trout. Obviously that's the brown trout influence.
the Male tigers seem to take on the brook trout characteristics while the females take on those of the brown. I agree they get excessive humps like brook trout. especially with the hatchery mutants that we see.
