Approximately 10% of all cyprinodontiform species—92 in all—are cited in the 2000 Red List of the International Union for Conservation of Nature and Natural Resources (IUCN) in the Extinct (10 species), Extinct in the Wild (5 species), Critically Endangered (18 species), Endangered (20 species), Vulnerable (25 species), Lower Risk/Near Threatened (3 species), and Data Deficient (11 species) categories. The cause of all freshwater fish extinctions and the establishment of the other categories of concern are due solely to the harmful effects of human intervention and not to the events of natural history. Sadly, a species of Cyprinodon described in 1993 was given the species name inmemoriam, since the species was extinct by the time it was described. The Red List is not a static document, and more species may be expected to appear there.
For instance, although huge tracts of the African rainforests are being cleared, not a single killifish from the affected areas is on the 2000 Red List. This is an extreme example of the category Data Deficient, in this case, no data at all. An undescribed Nothobranchius species from the Caprivi Strip of Namibia is the only African species listed as Endangered. All Nothobranchius habitats, being seasonal, are capable of being severely affected by human activity, so the absence of other Nothobranchius from the 2000 list offers small comfort. Numerous species are listed as Extinct in the Wild. Given the history of failure to keep Extinct in the Wild species, such as the monkey spring pupfish, alive as captive animals, unless they are successfully reintroduced into the wild, the future of such species is bleak.
For species listed in any category the reasons why they were listed are cited. Establishing whether a species is extinct is very difficult because of the nature of extinction. The absence of evidence is not necessarily evidence of absence. The difficulties are acute when the actual distribution of a species is imperfectly known or when its taxonomic limits have not been established or when there has been inadequate sampling. Harrison and Stiassny have reviewed this topic. Another 20 species are listed as regionally endangered by various states in the United States. These statistics need to be put into perspective. The percentage (10%) of the Cyprinodontiformes under threat is among the highest in the Actinopterygii, comparable to the carps, of the order Cypriniformes, with 12% of its 2,660 species appearing on the Red List. Live-bearers and killifishes have colonized marginal habitats easily degraded by human intervention or highly vulnerable to introduced exotic species. In addition, their distributions sometimes are highly localized, as, for example, in a single spring or pond. These factors account for the high level of threat occurring in this group.
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