Unique to the Cuatro Ciénegas Basin, the Coahuilan Pupfish is restricted to the saline waters of the area’s lakes, pools, marshes, and non-thermal springs and their outflows.
Although listed as Threatened by the Mexican government in 1994, the fish is common to remarkably abundant in restricted, local areas. They are usually found in warm (15-45°C) shallow (less than 25 cm) water, over a soft, flocculent, algae-rich bed, where they feed on detritus, algae and small invertebrates.
Behavior of the fish appears to be temperature dependent; below 15°C the sexes mix in loose aggregations of all sizes; at warmer temperatures males and females remain strictly segregated except during breeding. Between 25-45°C males form territories in extremely shallow water, usually less than 5 cm; territory size, posturing, and spawning display all vary with habitat. The females enter the territories only to spawn.
Eggs hatch in a few days and the young move freely throughout their environment. Growth is rapid, with sexual maturity achieved in a matter of weeks at summer temperatures.
— GCKA Newsletter, July 1998