Pecos pupfish  (Cyprinodon pecosensis)

Classified as Critically Endangered (CR) on the IUCN Red List (1).

Once abundant and relatively widespread, today this Critically Endangered fish persists in small numbers at just a few isolated sites (3). The diminutive Pecos pupfish has a stout body with rounded fins, with the male larger than the female. Throughout most of the year, both sexes are a dull brownish-green and marked with a series of dark spots and blotches (2). However, during the summer breeding season the male undergoes a striking colour change (2) (4), becoming an iridescent greyish-blue with creamy gill covers and a dark bar along the rear border of the tail fin (2).

Prior to the early 1980s, the Pecos pupfish was found throughout a 400 kilometre stretch of the Pecos River, which runs south from south-eastern New Mexico to Texas (2) (3). Today, because of interbreeding, the only remaining pure populations of the Pecos pupfish are found within Bitter Lake Wildlife Refuge in south-east New Mexico, in sinkholes, small lakes, tributaries and other water sources surrounding the main channel of the Pecos River (3) (5).

Within its current limited range, the Pecos pupfish occupies a wide range of habitats, from freshwater lakes to the extremely salty water found in desert sinkholes, where only a small number of species can survive (3) (6).

The Pecos pupfish is well-adapted to survive in the often harsh conditions found in its habitat; not only can it tolerate a range of salinities and temperatures (6), but it is also omnivorous and will consume a variety of foods such as algae, aquatic plants and insects (7).

The Pecos pupfish’s breeding season occurs from May to September, peaking around May and June (2) (6). The breeding males establish territories, which they aggressively defend from rival males as well as from other species. The best territories consist of plants and algae for the male to feed on, as well as an area of bare rock on which the female’s eggs can be deposited. These are, however, in short supply and fiercely competed for, hence many of the smaller males do not attempt to establish a territory, and retain their non-breeding colouration. Over the course of the breeding season, the female Pecos pupfish breeds with multiple partners, selecting the largest, most vividly coloured males. After mating, the female deposits a mass of eggs, which are left with the male to defend against predation, while the female searches for another mate (4). Pecos pupfish usually only live for a year, and each year’s breeding population is therefore composed of fish born in the previous summer (6).

During the early 1980s, the non-native sheepshead minnow (Cyprinodon variegates) was introduced to the Pecos River, and being closely related to the Pecos pupfish, the two species interbred to produce a hybrid species. Possessing greater swimming endurance than the Pecos pupfish, the hybrid species was able to outcompete breeding males for territories (5). This competitive advantage has allowed the hybrid to spread throughout the Pecos River, interbreeding with the Pecos pupfish, so that today significant pure Pecos pupfish populations only occur in sinkholes, tributaries and lakes in the Bitter Lake Wildlife Refuge in south-east New Mexico (3) (5). These small, isolated populations are highly vulnerable to disturbance, such as the pumping of groundwater for human use (7), and are also continually threatened by the introduction of the hybrid species from the Pecos River’s main channel (5).

A conservation agreement between state departments in New Mexico and the U.S. Fish and Wildlife Service has led to a number of conservation initiatives being employed to protect the Pecos pupfish. Artificial barriers have been placed around the Bitter Lake Wildlife Refuge to protect its population from invasion by the hybrid species. The other remaining populations are also being protected through the removal of non-native predators, and protection from groundwater pumping. These measures will help to ensure that, despite its highly restricted range, this Critically Endangered fish is protected from extinction (7).

View information on this species at the UNEP World Conservation Monitoring Centre.

To learn more about conservation initiatives in the United States visit:

• U.S. Fish and Wildlife Service:
  www.fws.gov