Killifish
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Killifish are small egg laying tooth-carp fish belonging to the order Cyprinodontiformes. This order is composed of several families including that of Poeciliidae that includes the guppy (Costa, 1998). The name killifish comes from the Dutch and means fish of the creek. Most killies are small, one to two inches (2.5 to 5 cm). The largest is under six inches (15 cm). Only a small handful are this large.
The term "killifish" is generally restricted to the egg laying members of this large group of fish. This term used to include the ricefish or medakas (genus Oryzias) of the order Beloniformes, but these were removed by Parenti (Parenti, 1981).
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Habitat
Killifish can be found in the Americas (e.g. the Mummichog(Fundulus), and Death Valley pupfish(Cyprinodon)), as far South as Argentina and as far North as Southern Ontario. They can also be found in southern Europe, most of Africa as far south as Kwa-Zulu Natal, South Africa. Killifish also occur in the Middle East, and Asia (as far east as Vietnam) and several Indian Ocean Islands. Killifish are not found in Australasia or northern Europe.
The majority of killifish live in permanent streams, rivers and lakes and live between 2 and 3 years. Such killifish are common in the Americas (Cyprinodon, Fundulus and Rivulus) and Africa, Asia, and Southern Europe (Aphanius, Aphyosemion, Aplocheilus, Epiplatys, Fundulopanchax, Lacustricola etc.).
Some specialized forms live in temporary ponds and flood plains. In Africa one finds the fish of the genus Nothobranchius and in South America several genera ranging from the cold water Austrolebias of Argentina and Uruguay to the more tropical Gnatholebias, Simpsonichthys and Terranatos. South American killies have both true annuals and non-annual species. The annuals survive no longer than 9 months and are used as models for studies on aging.
Territorial behavior
A small number of species will shoal while most will exhibit anti-social tendencies where territories are fixed and fiercely defended. Many species exist as passive tribes in small streams where dominant males will fix and defend a territory while allowing females and immature males to coinhabit the local area.
Diet
Killifish feed primarily on aquatic arthropods such as insect (mosquito) larvae, aquatic crustaceans and worms. It is reported by the killifish collector Rudolf Koubek that areas in Gabon where the streams lack killifish (due to pollution or other causes) are rife with malaria, which is spread by a mosquito. Some species of Orestias from Lake Titicaca are planktonic filter feeders. Others, such as Cynolebias and Megalebias species and Nothobranchius ocellatus are predatory and feed mainly on other fish.
Reproduction
Reproductive strategies of killifish are diverse. Some will spawn in no specific location while a small number of them (the Lampeyes) will spawn at specific sites or on specific environmental structures (e.g. Lamprichthys tanganicanus in rock crevices). Some species (e.g. Cyrinodon) will establish "nests" on the substrate wherein the male and various females will spawn. The annual killifish will spawn in the mud of the temporary ponds and floodplains. In the mud the eggs will cease development (diapause) dependent on the environmental conditions. There is some evidence that where the ponds do not dry out the eggs will develop as normal and hatch in the water. Where the ponds dry out the eggs will lie semi-dormant, developing slowly until the ponds fill again where upon the fry will hatch from the eggs and establish a new generation. One species of the genus Cynopoecilus practice a form of pseudo-internal fertilization and are thought to be an evolutionary pathway to the live bearing tooth carps (livebearers).
Killifish as pets
Many killifish are lavishly coloured; and most species are easy to keep and breed in an aquarium. Specimens can be obtained from specialist societies such as the American Killifish Association (http://www.aka.org), British Killifish Association (http://www.bka.org.uk) or Deutsche Killifisch Gemeinschaft (http://www.dkg.killi.org). Killies are seldom if ever found in pet shops but are very common on the online fish auction site Aquabid (http://www.aquabid.com). Good reference sources of killifish information are Killi.NET (http://new.killi.net) and killisite (http://www.killifish.us/). Freely reproducable images of most killies can be found at images.killi.net.
References
- Costa, WJM. (1998). Phylogeny and Classification of the Cyprinodontiformes (Euteleostei: Atherinomorpha): A Reappraisal. In Malabarba, L. et al. (eds), Phylogeny and Classification of Neotropical fishes part 6 (Atherinomorpha), Porto Alegre. 603 p.
- Huber, J. (2004). Killi-Data Online (http://www.killi-data.org)
- Parenti, Lynn R. (1981). A phylogenetic and biogeographical analysis of Cyprinodontiform fishes (Telostei, Alethrinimorpha). Bulletin of the American Museum of Natural History 168, article 4.ja:卵生メダカ