Nuptial Tubercle

Nuptial tubercles are conical, keratinous (or sometimes bony) structures that appear seasonally on the skin of male cyprinid fish and some other teleosts during the breeding season. They are most prominent on the snout, head, and anterior body. Their function is debated: they may stimulate females during spawning, provide traction when males press against females to stimulate egg release, or serve in male–male competition. They regress outside the breeding season. Tubercle number, size, and distribution pattern are sometimes taxonomically useful.