This unique species also lacks pelvic fins as well as the distinctive vertical barring so common among other pupfish and has a large head in proportion to its body. The female is colored yellowish-brown along the back. There is a dark edge on the dorsal fin and a vague dark bar through the area just in front of the tail fin. As with all pupfish, the sexes of this species are differently colored. The sides of the breeding male are blue and iridescent, the back is brownish to silver, and the gill covers are violet.
Young fish resemble the females.
In this system, one male will follow closely behind an egg-bearing female. The two will stay paired for up to an hour with aperiodic descents to the algae covered bottom for spawning. The Devil's Hole pupfish can spawn throughout the year, but concentrates most of its reproductive effort in April and May. Year-round spawning is made possible by the relatively constant 32.0 degrees C. water temperature of the spring pool. Growth of this species is closely related to the availability of food . The small 2x4 meter limestone shelf on which the fish spawns also provides a majority of the algae and much of the diatoms on which the fish feed.