The trout’s rough looking appearance might be the result of spawning. Rainbow trout spawn in late spring to early summer. When water temperature raise.
From the below website:
“… Rainbow trout spawn earlier in their lives than most other trout species (at roughly two years) and their spawning season occurs in the late spring and early summer as water temperatures rise. Brown trout spawn in the fall, …”
I’ve seen videos of trout spawning and they are into rough sex. The males often fight, biting one another to be the lucky guy that gets to pass on his dna to the next generation. Other species of trout will often bite the spawning female on the stomach to try to force her to release her eggs. So they can obtain a quick high protein meal.
I cannot find the video I recall seeing that better captures that behavior. It may be in one of the three Underwater Oz trout videos. But this video shows a bit of the rough and tumble of spawning.
Links to the youtube upload of the Underwater Oz videos were posted to this forum a couple of months ago. Viewing them again may find better video of the fighting and biting during the act of procreation.
Ah, I found the segment of the Underwater Oz video showing spawning behavior. However, they Brook Trout spawning in Oct. A rainbow trout does make an appearance, biting the spawning female on the stomach in an attempt to obtain a quick meal. Oz notes the biting will remove some of the protective mucous covering which could result in the fish becoming infected. My bet is that rainbow spawning behavior is similar. The females will also bite other females that try to move in on her selected spawning site.
Anyway, this behavior might account for missing scales and other damage causing the rough appearance.