Pupfish
Small fish noted for extreme habitats and rapid evolution.
Pupfish are small ray-finned fish from the family Cyprinodontidae, grouped into ten genera of killifish. They are best known for living in extreme, isolated environments across North America, South America, and the Caribbean. By August 2006, scientists had identified 120 named species and 9 subspecies. Many pupfish species are now extinct, and most surviving ones are listed as threatened or endangered. The name "pupfish" comes from the mating behavior of males, which was described by ichthyologist Carl L. Hubbs. He noticed their circling and tussling—actually aggressive territorial fights—and thought it resembled puppies playing.
Despite their name, pupfish are not closely related to the carp family, Cyprinidae. They were once thought to be related to pikes because of shared traits like a flat head, a protractile mouth with small, specialized teeth, large scales, and a poorly developed lateral line. Today, they are placed in the order Cyprinodontiformes. Fossil pupfish have been found in Oligocene and Miocene deposits in Europe. On San Salvador Island in the Bahamas, pupfish from different islands interbred, which helped them diversify into multiple species with distinct diets.
Most pupfish live in fresh or brackish water. Many species are ovoviviparous, meaning they give birth to live young. Males and females often look different: females are larger and less colorful, with smaller fins, while males may have a modified anal fin used for internal fertilization. Their diet mainly consists of algae, decaying plants, and any insects they can catch.
The genera include: †Carrionellus (fossil, Early Miocene of Ecuador), Cualac, Cubanichthys, Cyprinodon, Floridichthys, Garmanella, Jordanella, †Megupsilon (extinct 2014), Orestias, Pseudorestias, and Yssolebias (possibly extinct, known from one old specimen).
Pupfish evolution has been remarkably fast in some places. On San Salvador Island, pupfish in two small lakes have diversified at rates 50 to 130 times faster than other pupfish species—the fastest documented morphological change in any fish. This is thought to be driven by different ecological niches. Three species there all live in salty lakes but exploit different food sources: one feeds only on the scales of other pupfish, while another has a modified jaw to eat snails and ostracods.
Before the 1990s, Mexico’s Lake Chichancanab held five pupfish species
- field
- Ichthyology
- known_for
- Extreme habitat adaptation and rapid evolution
- number_of_species
- 120 nominal species and 9 subspecies (as of August 2006)
- primary_regions
- North America, South America, Caribbean region
- notable_species
- Devils Hole pupfish (Cyprinodon diabolis)
Lore & Background
Pupfish are inhabitants of fresh and brackish waters. Many species are ovoviviparous; often the sexes are dissimilar, the female being larger and less brilliantly coloured, with smaller fins; the anal fin of the male may be modified into an intromittent organ. Most pupfishes' diet consists mainly of algae, decaying vegetation, and any insects they can get. Pupfish are facultative anaerobes.
Pupfish on the island of San Salvador, Bahamas, have a large adaptive diversification in only two small lakes. They evolve 50–130 times faster than any other species of pupfish, the fastest morphological diversification seen in any fish documented. Three species there all live in salty lakes and take advantage of different food sources: one feeds on only the scales of other pupfish, another has a modified jaw to eat snails and ostracods. Before the 1990s, Lake Chichancanab in Mexico contained five species of pupfish, including the largest pupfish, Cyprinodon maya, which ate other fish, and Cyprinodon simus, which ate zooplankton; these species are now considered extinct in the wild because of an invasive species of African tilapia.
Reader's Guide
Pupfish are significant as a model of rapid evolutionary diversification in isolated, extreme environments. Their ability to adapt to hot, saline, and oxygen-poor waters—including being facultative anaerobes—illustrates the resilience of life under harsh conditions. The Devils Hole pupfish, native to a single geothermal pool in Nevada, has been in a nearly steady decline since 1995, reaching close to extinction at 35–68 fish in 2013, and is considered one of the world's rarest fish. The Death Valley pupfish, once part of a single species in glacial Lake Manly, diverged into subspecies as the lake dried and separated. The San Salvador pupfish show the fastest documented morphological diversification in any fish, evolving 50–130 times faster than other pupfish. Their legacy includes highlighting conservation challenges, as several species are extinct or endangered due to habitat loss and invasive species, and providing insight into the mechanisms of adaptive radiation.
Did You Know?
- Pupfish are facultative anaerobes, able to survive without oxygen.
- The Devils Hole pupfish population fluctuated between 37 and 400 fish after 2005, with 35–68 fish in 2013.
- Pupfish on San Salvador Island evolve 50–130 times faster than any other pupfish species.
- The common name derives from males' mating behavior, which resembles puppies at play.
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