pearl organ

breeding tubercle (usually small, raised, epidermal structures on regions of the head, body, or fin rays where two individuals come in contact. May consist of aggregations of non-keratinized epidermal cells, the same with a light, superficial keratinized cuticle, or with substantial number of fully keratinized cells that are organized to form a discrete, usually conical cap. Breeding tubercles may function to maintain body contact between the sexes during spawning; in the defence of nests and territories; in the stimulation of females in courtship; and in some forms perhaps in sex and species recognition. Also called nuptial tubercles. Found in 15 families of 4 orders; Salmoniformes, Gonorhynchiformes, Cypriniformes, and Perciformes (Wiley and Collette, 1970))

see preferred term: tubercle, breeding. The term pearl organ has been applied vaguely and is not apt since the structure is often not pearl colored (usually small, raised, epidermal structures on regions of the head, body, or fin rays where two individuals come in contact. May consist of aggregations of non-keratinized epidermal cells, the same with a light, superficial keratinized cuticle, or with substantial number of fully keratinized cells that are organized to form a discrete, usually conical cap. Breeding tubercles may function to maintain body contact between the sexes during spawning; in the defence of nests and territories; in the stimulation of females in courtship; and in some forms perhaps in sex and species recognition. Also called nuptial tubercles. Found in 15 families of 4 orders; Salmoniformes, Gonorhynchiformes, Cypriniformes, and Perciformes (Wiley and Collette, 1970))