Nuptial tubercles

"Pearl organ" redirects here. For the obscure organ of a deep-sea fish, see Pearleye.

Nuptial tubercles on stone-roller, Campostoma anomalum

Nuptial tubercles or breeding tubercles (also called pearl organs or nuptial efflorescence) are noticeable skin roughness or horny nodules that form on male fish during breeding. They are made of keratin, the same material as hair, hooves, and fingernails.