With the exception of Exoglossum , nest-building minnows exhibit strong sexual dimorphism. Males are larger and more brightly colored than females and develop keratinized structures called breeding tubercles on the head, body, and fins. The largest breeding tubercles are found on the head and are extremely large in some species. Functions of breeding tubercles on the head are thought to include display, defense, and stimulation of females. Tubercles on the body and fins are thought to assist in holding, or maintaining contact with, females during spawning.
Males are aggressive and defend positions over pits.
Females congregate nearby and enter the pits individually. Spawning occurs as one or more males converge on a female in a pit. These species may spawn in association with each other or over the nests of other species of minnows. Males excavate pits in gravel runs by removing stones with their mouths and piling them immediately upstream. Spawning occurs when a female enters the pit, and eggs are covered with substrate by the male, who then extends the pit downstream.