Single male creek chubs build nests and guard them from intruders, especially nonspecific males. Such territoriality and the apparent shortage of suitable nest sites result in a complex social system and aggression among breeding males. Challenges by similarly sized males result in complex displays called parallel swims. Smaller males that attempt to take over nests are driven away, often by a display of head tubercles by the resident male. Many males do not build their own nests, but instead act as satellites, waiting for opportunities to temporarily occupy the nests of territorial males and spawn.
Male chubs begin nest-construction by excavating a pit in gravel substrate of a stream.
The pit is then covered- with stones the male carries to the site in his mouth, and a large mound is constructed. Spawning occurs in small pits dug on top of the mound by the male. Nest-construction in cutlips minnows is similar except the nest is not started as a pit, and spawning occurs on the upstream slope of the mound rather than in pits dug by the male. Although males of all other nest-building minnows develop conspicuous breeding tubercles, male Exoglossum do not. Little is known about the breeding behavior and social systems of nest-building minnows.