Shore-spawners exhibit high reproductive synchrony. They arrive at the spawning site in schools, settle in colonies, spawn within hours, and are dead within days. Stream-spawners demonstrate less synchrony, arrive paired or as individuals, settling over several days, and often persisting for several weeks. Stream-spawners attempt to pair with a female, exhibiting aggressive interactions with other competing males. Large males typically enjoy pairing more than smaller males.
Some small males sneak alongside a spawning pair, and release milt.
Shore-spawning males, on the other hand, do not fight, but press their ventral surface into substrate crevices where females will spawn. They associate with the oviposition site rather than the females. These differences are suggested to be the outcome of different selective pressures in the two spawning habitats. Behavioural evolution of shore-spawners is thought to be heavily constrained by predation at the beach spawning site. The tendency away from synchrony increased male availability, thus males engaged in combat to gain access to receptive females.