Cyprinodon

The Potosí pupfish, Cyprinodon alvarezi, is a pupfish from a single isolated spring near El Potosí in Nuevo León state, northern Mexico. It has been extinct in nature since the late 1990s, after the spring-fed pond at La Hediondilla dried up through extraction of its water for irrigation and other human uses. The species now exists only in captivity, and its preservation means it is not recommended for the community fish keeper.

The durophage pupfish, Cyprinodon brontotheroides, is a pupfish endemic to six hypersaline lakes on San Salvador Island in the Bahamas. A specialised predator of hard-shelled invertebrates, particularly gastropods and ostracods, it has a shortened upper jaw and a protruding nasal region, and no other Cyprinodon species is adapted to hard-shelled prey. It occurs alongside C. variegatus in all six lakes and with C. desquamator in four of them.

The scale-eating pupfish, Cyprinodon desquamator, is a pupfish endemic to six hypersaline lakes on San Salvador Island in the Bahamas. A specialised lepidophage, it takes approximately half its diet as the scales of other fishes, and its large supra-terminal jaws and elongate body are adapted to a fast biting action. No other Cyprinodon species feeds on fish scales, and it lives alongside C. variegatus in all six lakes.

The Julimes pupfish, Cyprinodon julimes, is known only from a geothermal spring in the middle Río Conchos basin, Chihuahua state, northern Mexico. The water there fluctuates between 38 and 48 °C, and the spring is considered one of the hottest environments inhabited by fish in the world. Its closest relatives are C. eximius and C. pachycephalus.

Cyprinodon pachycephalus is a pupfish endemic to the thermal spring of San Diego de Alcalá and its distributaries in Chihuahua state, northern Mexico. The springs produce water at a constant 43.8 °C, cooling downstream, and in the lower part of the system it forms natural hybrids with the congener C. eximius.

The sheepshead 'minnow', Cyprinodon variegatus, is a pupfish ranging from the northeastern U.S.A. to northeastern Mexico, the Bahamas and Antilles. It tends to be most common in brackish to hypersaline environments such as coastal salt marshes, lagoons and estuaries. On San Salvador Island in the Bahamas it appears to be the parent of a group of species living in sympatry and exploiting diverse but specific resources.

The Charco Palma pupfish, Cyprinodon veronicae, is a pupfish known only from the spring Ojo de Agua Charco Azul in Nuevo León, Mexico. The Bolsón de Sandia spring system has been dry since the late 1990s because of water extraction by local communities, and all four Cyprinodon species described from it are now considered extinct in the wild. Nuptial males are violaceous blue.