It has been sampled, just not extensively. Guarantee there's been some kind of bridge work, repairs, assessments etc that would have required at least limited sampling over the past couple years. Fish can be injured as fry and grow to be large adults too, it happens. I caught a 14'' bow a few years ago with the same look, it was tagged actually. I looked into it and that fish had been captured a few years earlier, as a healthy normal looking yearling. Alternatively it could also be a spinal deformity, it does occur in nature; Its just more likely it was electrofishing.