Fish deformities occur at similar rates to many other organisms.
The vast majority of deformities result in individuals without viability. Most of them we never see.
It is my personal belief, from what I've seen with striped bass hybrids, that populations that are provided with pelleted feed result in higher deformity rates amongst adults, due to the fact that fish with deformities aren't forced to compete for food with their physical prowess. I.E., this fish wouldn't have a chance in Lake Erie, but did just fine with easy to "capture" pellets.
A corollary would be near-sightedness in humans. In the wild, it would be selected out, but in our "pellet-fed" world we just make glasses or contacts and everybody gets along just fine.
