Killifish
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A killifish is any of various small, mainly oviparous (egg-laying) cyprinodont fish (order Cyprinodontiformes, family Cyprinodontidae). The name killifish is derived from the Dutch word "kilde", meaning small creek, puddle. Most killies are small fish, one to two inches (2.5 to 5 cm). The largest is under six inches (15 cm), but only a few species are this large. Although killifish is sometimes used as an English equivalent to Cyprinodontidae, some species belonging to this family have their own common names, such as the pupfish and the mummichog.
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[edit] Range and habitat
Killifish are found mainly in fresh or brackish waters in the Americas, as far south as Argentina and as far north as southern Ontario. There are also species in southern Europe, in much of Africa as far south as Kwa-Zulu Natal, South Africa, in the Middle East and Asia (as far east as Vietnam), and on several Indian Ocean islands. Killifish are not found in Australia, Antarctica, or northern Europe.
The majority of killifish are found in permanent streams, rivers, and lakes, and live between two and three years. Such killifish are common in the Americas (Cyprinodon, Fundulus and Rivulus) as well as in Africa and Asia (Aphyosemion, Aplocheilus, Epiplatys, Fundulopanchax, Lacustricola etc.) and southern Europe (Aphanius).
Some specialized forms live in temporary ponds and flood plains, and typically have a much shorter lifespan. Such "annual" species live no longer than nine months, and are used as models for studies on aging. Examples include the African genus Nothobranchius and South American genera ranging from the cold water Austrolebias of Argentina and Uruguay to the more tropical Gnatholebias, Pterolebias, Simpsonichthys and Terranatos.
[edit] 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.
[edit] 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.
[edit] 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. Cyprinodon) 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 (semi-annual). Where the ponds dry out the eggs will lie semi-dormant, developing slowly until the ponds fill again whereupon the fry will hatch from the eggs and establish a new generation.
Males of some species in the genera Campellolebias and Cynopoecilus possess a gonopodium and practice a form of pseudo-internal fertilization, and are thought to be an evolutionary pathway to the live bearing tooth carps (livebearers). The species Rivulus marmoratus is the only known naturally occurring, truly self-fertilizing vertebrate. Furthermore, they are always either male or hermaphroditic; females of the species don't seem to exist. Only about 5% of a population are born as males; after 3-4 years about 60% of the (self-fertilizing) hermaphrodites transform into secondary males by losing female structures and functions. The proportion of males depends on the environmental temperature: below 20°C (68°F) the majority are males, and above 25°C (77°F) all specimens are hermaphrodites.
[edit] 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, British Killifish Association or Deutsche Killifisch Gemeinschaft. Killies are seldom if ever found in pet shops but are very common on the online fish auction site Aquabid. A good reference source of killifish information is Killi.NET. Copyrighted yet freely reproducible images of most killies can be found at images.killi.net.
[edit] External links
[edit] References
- Costa, Wilson J.E.M. (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.
- Costa, Wilson J.E.M. (2004). A new killifish genus and species from the coastal plains of north-eastern Brazil (Teleostei: Cyprinodontiformes: Rivulidae). Zootaxa 642:1-10. Magnolia Press. 500 p. (Regarding Kryptolebias marmoratus (synonym Rivulus marmoratus), see Fishbase Ref. 52570.)
- Huber, J. (2004). Killi-Data Online
- 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.
