Cyprinodon


Cyprinodon is a genus of small pupfishes found in waters that range from fresh to hypersaline. The genus is primarily found in Mexico, the Caribbean Islands and southern United States, but C. variegatus occurs as far north as Massachusetts and along the entire Gulf of Mexico coastline, and C. dearborni and C. variegatus are found in northern South America. Many species have tiny ranges and are highly threatened, in some cases already extinct. Cyprinodon are small; the largest reaches in length and most other species only reach about half that size.

Distribution and habitat

A few Cyprinodon species have quite large ranges, notably C. variegatus, but the vast majority have small ranges, typically restricted to one or two Mexican states or US states, Hispaniola, or a Bahaman island. C. longidorsalis and C. diabolis have both been said to have the smallest native range of any vertebrate species, with the former being restricted to a spring pool that covers about and the latter to an shelf in a spring pool, but C. longidorsalis is now only found in captivity as its habitat has disappeared. While most Cyprinodon species have separate distributions, seven are endemic in Lake Chichancanab in Quintana Roo, Mexico, and three live in the hypersaline lakes on San Salvador Island in the Bahamas. In a few other cases separate species do come into contact towards the edges of their distributions where they often hybridize, notably C. eximius X C. pachycephalus and C. atrorus X C. bifasciatus, but also C. variegatus in places where it has been introduced by humans into the ranges of other Cyprinodon species.
Although the individual Cyprinodon species often have a highly specific habitat, overall the genus occurs in a remarkably range of places, such as springs, pools, lakes, coastal lagoons, creeks, streams and rivers. Their salinity and temperature range is very broad, like those living in hot springs, and those of hypersaline habitats where the salinity far exceeds that of sea water. Certain species may even experience very large variations in the temperature and salinity over a relatively short period. For example, some populations of C. variegatus live in water where the temperature has been known to change from in less than 24 hours. Some populations of C. nevadensis tolerate water temperatures between, and C. salinus live in waters where the temperature may change by as much as in a day and in a season. Furthermore, the salinity of C. salinus' habitat may vary from less than one-third of that of sea water to almost five times as much as sea water in a season.

Conservation status

Most species in the genus are seriously threatened. C. arcuatus, C. ceciliae, C. inmemoriam, C. nevadensis calidae and an undescribed species popularly known as the "Perrito de Sandia" are already extinct. C. arcuatus was restricted to springs in the US state of Arizona and probably also in the Mexican state of Sonora, while all the others were restricted to spring systems in Mexico.
Three species from southwestern Nuevo León, C. alvarezi, C. longidorsalis and C. veronicae, have become extinct in the wild, only surviving in captivity. A few other Mexican species still considered endangered or vulnerable by the IUCN, including at least C. maya, C. simus and C. verecundus of Lake Chichancanab, also appear to only survive in captivity. Several others have very small remaining populations in the wild. Among the species that survive in the wild, the rarest is perhaps C. diabolis from the tiny Devils Hole in Nevada; in recent decades its population has fluctuated between a few tens and a few hundred individuals. Primary threats to pupfish are habitat loss due to water extraction, drought and pollution, and introduced species.

Behavior

Feeding

Most Cyprinodon species feed on algae, cyanobacteria and detritus, but may also supplement their diet with small crustaceans and aquatic insect larvae. Some species mainly feed on small animals like aquatic insects. C. variegatus, a species that otherwise has a diet typical of pupfish, will clean other fish by feeding on parasites on their body.
In the two places where several species live together they have diverged into different niches, including the fish-eating C. maya, zooplankton-eating C. simus, amphipod- and bivalve-eating C. labiosus and C. verecundus, scale-eating C. desquamator, and ostracod- and gastropod-eating C. brontotheroides.

Breeding

Cyprinodon pupfish are short-lived, typically reaching an age of no more than a year in the wild, although some may reach as much as three years. Especially those from habitats that experience major environmental fluctuations rapidly reach maturity and are already able to breed when 1–1.5 month old. Despite some species' ability to survive in a wide temperature range, their requirements for breeding often are much more specific. For example, although some populations of C. nevadensis can live in water that ranges between, they only breed from. However, there are exceptions like C. rubrofluviatilis that will breed at a relative wide range from. Consequently, pupfish living in stable habitats breed year-round, but those in more seasonal habitats generally only at certain times of the year where the conditions are optimal. When breeding, males assume a relatively bright nuptial coloration.
There are two primary breeding strategies: In species of small isolated habitats like springs, each large male defends a territory and displays to visiting females that will lay their eggs inside the territory. In at least some species, small males will attempt to fertilize eggs by sneaking into a territory of a larger male. Once deposited, neither sex cares for the eggs, although they do get a level of protection by being inside the territory of a male. A male will attempt to attract several females to lay their eggs in his territory and a female may lay eggs in the territories of several males. Another breeding strategy is used by species that inhabit rivers. Here the males do not maintain a territory and groups of pupfish gather to breed. A male typically will lead a female to the edge of the group to spawn, although on occasion it may occur in the middle of the group. The eggs of Cyprinodon pupfish are adhesive and stick to the substrate, or they are covered in sand.

Species

There are currently 49 recognized species in this genus: