Pearl rash - cone-shaped bumps covered with horny substance, formed by the overgrowth of the epidermis under the influence of sex hormones during the breeding season. After spawning, pearl rash disappears without leaving a trace.

Pearl rash occurs on the head in carp, whitefish and smelt. In carps, the rash appears on the body of both males and females, but the former have more of it and it is spread over almost the entire body.

During the spawning period, the so-called pearl rash appears on the trunk and head - bumps formed by overgrowth of the epidermis, which cone-like extends outward. On top of the bump is covered with horny substance. Developing during the reproductive period under the influence of sex hormones, pearl rash will later disappear without leaving any trace.