How common are fish like this?

[Dewayne French]

It occurs to the fish in the egg form most often Genetic or Vitamin related from the female fish. Very rarely happens to adult fish except in extreme circumstances like lighting strikes and electric shocks to hatchery ponds brood fish although it could happen to lake coves, as we have all seen lighting strike the water. If your around a hatchery that is or does hatching of eggs it is pretty cool to go watch which ever species it is. It does occur in all species and usually is in a small percentage of the population.

[Hammer time]

Imo I think like others that something happened during hatching or very young and grew into the mishap. Have caught all types and feel sorry for them but they seem fine.

So like always thanks for biting and see you again sometime.