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. Found in 15 families of 4 orders; Salmoniformes, Gonorhynchiformes, Cypriniformes, and Perciformes (Wiley and Collette, 1970) (Ref. 28)