Horny growths on the head and body of male carp, whitefish and salmonids during the spawning season. This phenomenon is less pronounced in females. The appearance of "pearl rash" - keratinised tubercles of epithelium on the head and body of many carp, chub and whitefish - should be attributed to mating habits. Such mating apparel as tubercles is a natural stimulant that causes the sexual products to recoil.