{{short description|Any of various oviparous cyprinodontiform fish}} [[Image:Nothobranchius rachovii male.jpg|thumb|240px|A bluefin notho killifish, ''Nothobranchius rachovii'', from East Africa]]
A '''killifish''' is any of various oviparous (egg-laying) cyprinodontiform fish,<ref name="Albert-et-al-2020">{{cite journal | last1=Albert | first1=James S. | last2=Tagliacollo | first2=Victor A. | last3=Dagosta | first3=Fernando | title=Diversification of Neotropical Freshwater Fishes | journal=Annual Review of Ecology, Evolution, and Systematics | publisher=Annual Reviews | volume=51 | issue=1 | date=2020-11-02 | issn=1543-592X | doi=10.1146/annurev-ecolsys-011620-031032 | pages=27–53| s2cid=225478064 | doi-access=free }}</ref> including families Aplocheilidae, Pantanodontidae, Cyprinodontidae, Fundulidae, Nothobranchiidae, Profundulidae, Aphaniidae and Valenciidae. All together, there are 1,270 species of killifish, the biggest family being Rivulidae, containing more than 320 species.<ref>[http://filaman.ifm-geomar.de/Nomenclature/NominalSpeciesList.cfm?Family=Rivulidae List of Nominal Species of Rivulidae (Rivulines)]''FishBase''. Ed. Rainer Froese and Daniel Pauly. May 2007 version. N.p.: FishBase, 2007. {{Webarchive|url=https://web.archive.org/web/20070930094243/http://filaman.ifm-geomar.de/Nomenclature/NominalSpeciesList.cfm?Family=Rivulidae |date=2007-09-30 }}</ref> As an adaptation to living in ephemeral waters, the eggs of most killifish can survive periods of partial dehydration. Many of the species rely on such a diapause, since the eggs would not survive more than a few weeks if entirely submerged in water. The adults of some species, such as ''Kryptolebias marmoratus'', can additionally survive out of the water for several weeks.<ref>[https://www.reuters.com/article/oddlyEnoughNews/idUSN1522299020071115?pageNumber=1 "Tropical fish can live for months out of water"], Reuters, Wed Nov 14, 2007 9:05pm GMT</ref> Most killifish are small, measuring from {{convert|2.5 to 5|cm|in|0}}, with the largest species growing to just under {{convert|15|cm|in|0}}.
The word ''killifish'' is of uncertain origin, but is likely to have come from the Dutch ''kil'' for a kill (small stream).<ref>{{Cite book|page=198|url=https://books.google.com/books?id=qIsDdUSYJMIC&q=etymology+of+killifish&pg=PA198|title=Cookies, Coleslaw and Stoops: The Influence of Dutch on the North American Languages|first=Nicoline|last=van der Sijs|publisher=Amsterdam University Press|date=2009|isbn=978-90-8964-124-3}}</ref> Although killifish is sometimes used as an English equivalent to the taxonomical term Cyprinodontidae, this is only one of several families that are referred to as killifish. Cyprinodontidae more specifically refers to the pupfish family.
==Range and habitat== [[Image:Cyprinodon diabolis.jpg|thumb|240px|Devils Hole pupfish, ''Cyprinodon diabolis'', from Death Valley National Park]] Killifish are found mainly in fresh or brackish waters in the Americas, as far south as Argentina and as far north as southern Ontario and even Newfoundland and Labrador.<ref>As of summer 2023, the Suncor Energy Fluvarium in St. John's, Newfoundland notes, that the Newfoundland population of fundulus diaphanous (banded killifish) is listed as species of Special Concern under Canada's Species at Risk Act. </ref> There are also species in southern Europe, in much of Africa as far south as KwaZulu-Natal, South Africa, in the Middle East and Asia (as far east as Vietnam), and on several Indian Ocean islands.
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 (including ''Aphyosemion'', ''Aplocheilus'', ''Epiplatys'', ''Fundulopanchax'' and ''Lacustricola'') and southern Europe (''Aphanius''). Some of these habitats can be rather extreme; the only natural habitat of the Devils Hole pupfish (''Cyprinodon diabolis'') is Devils Hole: a cavern at least {{convert|91|m|ft|0}} deep, branching out from a small opening at the surface, approximately {{convert|1.8|m|ft|0}} by {{convert|5.5|m|ft|0}} wide.
Some specialized forms live in temporary ponds and flood plains, and typically have a much shorter lifespan. Such species, known as "annuals", 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'',<ref name="Costa">{{cite journal |last1=Costa |first1=Wilson J.E.M. |title=The Neotropical annual killifish genus Pterolebias Garman (Teleostei: Cyprinodontiformes: Rivulidae): phylogenetic relationships, descriptive morphology, and taxonomic revision |journal=Zootaxa |date=21 October 2005 |volume=1067 |issue=1 |pages=1–36 |doi=10.11646/zootaxa.1067.1.1 }}</ref> ''Simpsonichthys'' and ''Terranatos''.
==Territorial behaviour== [[Image:Fundulus cingulatus.jpg|thumb|240px|''Fundulus auroguttatus'', a non-annual North American killifish similar to ''Fundulus chrysotus'' known as a topminnow]] A small number of species will shoal while most are territorial to varying degrees. Populations can be dense and territories can shift quickly, especially for species of the extreme shallows (a few centimetres of water). Many species exist as passive tribes in small streams where dominant males will defend a territory while allowing females and immature males to pass through the area. In the aquarium, territorial behaviour is different for every grouping, and will even vary by individuals. In a large enough aquarium, most species can live in groups as long as there are more than three males.
==Diet== Killifish feed primarily on aquatic arthropods such as insect (mosquito) larvae, aquatic crustaceans and worms. 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. The American Flagfish (''Jordanella floridae'') feeds heavily on algae and other plant matter as well as aquatic invertebrates. ''Nothobranchius furzeri'' needs much food because it grows quickly, so when food supplied is inadequate, bigger fish will eat the smaller fish.<ref>{{cite web | title = Species File: ''Nothobranchius furzeri'' | publisher = Killi.co.uk | date = 2009–2013 | url = http://www.killi.co.uk/speciesProfile/Nothobranchius/furzeri/ | access-date = 2013-02-08 }}</ref>
==In lifespan research== [[Image:Nothobranchius furzeri GRZ thumb.jpg|thumb|240px|A male ''Nothobranchius furzeri'' GRZ <br />(from Gonarezhou National Park)]]
Some strains have a lifespan as short as several months and can thus serve as a model for biogerontological studies.<ref>{{cite journal|vauthors=Terzibasi E, Valenzano DR, Benedetti M, Roncaglia P, Cattaneo A, Domenici L, Cellerino A|title=Large differences in aging phenotype between strains of the short-lived annual fish ''Nothobranchius furzeri''|journal=PLoS ONE|volume=3|issue=12|year=2008|article-number=e3866|pmid=19052641|doi=10.1371/journal.pone.0003866|pmc=2585814|bibcode=2008PLoSO...3.3866T|doi-access=free}}</ref><ref name="pmid22384364">{{cite journal|vauthors=Valenzano DR, Sharp S, Brunet A|pmid=22384364|pmc=3276177|doi=10.1534/g3.111.001271|title=Transposon-Mediated Transgenesis in the Short-Lived African Killifish ''Nothobranchius furzeri'', a Vertebrate Model for Aging|journal=G3: Genes, Genomes, Genetics|volume=1|issue=7|year=2011|pages=531–538}}</ref><ref name="doi10.1016/j.cell.2015.01.038">{{Cite journal|last1=Harel|first1=I.|last2=Benayoun|first2=B. R. N. A.|last3=Machado|first3=B.|last4=Singh|first4=P. P.|last5=Hu|first5=C. K.|last6=Pech|first6=M. F.|last7=Valenzano|first7=D. R.|last8 =Zhang|first8=E.|last9=Sharp|first9=S. C.|last10 =Artandi|first10=S. E.|last11=Brunet|first11=A|doi=10.1016/j.cell.2015.01.038|pmid=25684364|title=A Platform for Rapid Exploration of Aging and Diseases in a Naturally Short-Lived Vertebrate|journal=Cell|volume=160|issue=5|pages=1013–26|year=2015|pmc=4344913}}</ref><ref name="pmid26659161">{{cite journal|author=Callaway E|title=Short-lived fish may hold clues to human ageing|journal=Nature | volume=528|issue=7581|year=2015|page=175|doi=10.1038/nature.2015.18945 | pmid= 26659161 |bibcode=2015Natur.528..175C|doi-access=free}}</ref><ref name="pmid 25923786">{{cite journal |vauthors=Cellerino A, Valenzano DR, Reichard M | title=From the bush to the bench: the annual ''Nothobranchius'' fishes as a new model system in biology | journal=Biological Reviews of the Cambridge Philosophical Society | volume=91 | issue=2 | year=2016|pages=511–533 | doi=10.1111/brv.12183 | pmid= 25923786 | s2cid=3963445 | url=https://repository.publisso.de/resource/frl:6405001/data | doi-access=free | hdl=11384/61025 | hdl-access=free }}</ref> The African turquoise killifish (''Nothobranchius furzeri'') is the shortest-living vertebrate that can be bred in captivity, having a lifespan of between three and nine months.<ref name="pmid22384364" /><ref name="doi10.1016/j.cell.2015.01.038"/> Sexual maturation occurs within 3–4 weeks, with fecundity peaking in 8–10 weeks.<ref name="pmid26839399">{{cite journal|vauthors=Kim Y, Nam HG, Valenzano DR | title=The short-lived African turquoise killifish: an emerging experimental model for ageing|journal=Disease Models & Mechanisms|volume=9 | issue=2|year=2016|pages=115–129|doi=10.1242/dmm.023226|pmc=4770150|pmid=26839399}}</ref>
''Nothobranchius furzeri'' shows no signs of telomere shortening, reduced telomerase activity, or replicative senescence with age, despite its short lifespan.<ref>{{cite journal |vauthors=Hartmann N, Reichwald K, Lechel A, Graf M, Kirschner J, Dorn A, Terzibasi E, Wellner J, Platzer M, Rudolph KL, Cellerino A, Englert C | title=Telomeres shorten while Tert expression increases during ageing of the short-lived fish ''Nothobranchius furzeri'' | journal=Mechanisms of Ageing and Development | volume=130 | issue=5 | year=2009 | pages=290–296 | pmid=19428446 | doi=10.1016/j.mad.2009.01.003 | s2cid=10813587 | doi-access=free }}</ref><ref>{{cite journal |vauthors=Graf M, Hartmann N, Reichwald K, Englert C | title=Absence of replicative senescence in cultured cells from the short-lived killifish ''Nothobranchius furzeri'' | journal=Experimental Gerontology | volume=48 | issue=1 | year=2013 | pages=17–28 | pmid=22445733 | doi=10.1016/j.exger.2012.02.012 | s2cid=11729069 }}</ref> Nonetheless, lipofuscin accumulates in the brain and liver (associated with age-related neurodegeneration), and there is an increased risk of cancer with age.<ref name="pmid26839399" /> Calorie restriction reduces these age-related disease conditions.<ref name="pmid26839399" /> Resveratrol has been shown to increase the mean (56%) and maximum life span (59%) of ''Nothobranchius furzeri'',<ref name="pmid16732220">{{cite journal | vauthors=Baur JA, Sinclair DA | title=Therapeutic potential of resveratrol: the in vivo evidence| journal=Nature Reviews Drug Discovery | volume=5 | issue=6 | pages=493–506 | year=2006 | doi = 10.1038/nrd2060| pmid=16732220| s2cid=36628503}}</ref><ref name="pmid16461283">{{cite journal | vauthors=Valenzano DR, Terzibasi E, Genade T, Cattaneo A, Domenici L, Cellerino A | title=Resveratrol prolongs lifespan and retards the onset of age-related markers in a short-lived vertebrate | journal=Current Biology | volume=16 | issue=3 | year=2006 | pages=296–300 | doi=10.1016/j.cub.2005.12.038 | pmid=16461283 | s2cid=1662390 | doi-access=free | bibcode=2006CBio...16..296V | hdl=11384/14713 | hdl-access=free }}</ref> but resveratrol has not been shown to have this effect in mammals.<ref name="pmid25640851">{{cite journal | vauthors=Bhullar KS, Hubbard BP | title=Lifespan and healthspan extension by resveratrol | journal=Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease | volume=1852 | issue=6 | year=2015 | pages=1209–1218 | doi=10.1016/j.bbadis.2015.01.012 | pmid=25640851 | doi-access=free }}</ref><ref name="pmid22451473">{{cite journal | vauthors=Strong R, Miller RA, Nadon NL, Harrison DE | title=Evaluation of resveratrol, green tea extract, curcumin, oxaloacetic acid, and medium-chain triglyceride oil on life span of genetically heterogeneous mice| journal= The Journals of Gerontology Series A: Biological Sciences and Medical Sciences| volume=68 | issue=1 | pages=6–16 | year=2013 | doi = 10.1093/gerona/gls070 | pmc=3598361 | pmid=22451473}}</ref><ref name="pmid16732220" />
Transferring the gut microbiota from young killifish into middle-aged killifish significantly extends the lifespans of the middle-aged killifish.<ref name="pmid28826469 ">{{cite journal | vauthors=Smith P, Willemsen D, PopkesM | title=Regulation of life span by the gut microbiota in the short-lived African turquoise killifish | journal=eLife | volume=6 | issue=e27014 | year=2017 | doi = 10.7554/eLife.27014 |pmid=28826469| pmc=5566455 | doi-access=free }}</ref><ref name="pmid31403049 ">{{cite journal | vauthors=Tibbs TN, Lopez LR, Arthur JC | title=The influence of the microbiota on immune development, chronic inflammation, and cancer in the context of aging | journal=Microbial Cell | volume=6 | issue=8 | pages=324–334 | year=2019 | doi = 10.15698/mic2019.08.685 | pmc=6685047 | pmid=31403049 }}</ref>
Transgenic strains have been made,<ref>{{cite journal |vauthors=Valenzano DR, Sharp S, Brunet A | title=Transposon-Mediated Transgenesis in the Short-Lived African Killifish ''Nothobranchius furzeri'', a Vertebrate Model for Aging | journal=G3: Genes, Genomes, Genetics | volume=1 | issue=7 | year=2011 | pages=531–538 | pmid=22384364 | doi=10.1534/g3.111.001271 | pmc=3276177}}</ref> and precise genome editing was achieved in ''Nothobranchius furzeri'' using a draft genome and the CRISPR/Cas9 system.<ref name="doi10.1016/j.cell.2015.01.038"/> By targeting multiple genes, including telomerase, the killifish can now be used as an attractive vertebrate model organism for aging and diseases (such as ''Dyskeratosis congenita'').<ref name="doi10.1016/j.cell.2015.01.038"/> Sequencing the whole killifish genome indicated modification to the IGF-1 receptor gene.<ref name="pmid26638078">{{cite journal |vauthors=Valenzano DR, Benayoun BA, Singh PP, Zhang E, Etter PD, Hu CK, Clément-Ziza M, Willemsen D, Cui R, Harel I, Machado BE, Yee MC, Sharp SC, Bustamante CD, Beyer A, Johnson EA, Brunet A | title=The African Turquoise Killifish Genome Provides Insights into Evolution and Genetic Architecture of Lifespan | journal=Cell | volume=163 | issue=6 | year=2015 | pages=1539–1554| doi=10.1016/j.cell.2015.11.008 | pmid=26638078 | pmc=4684691 }}</ref>
==As pets== [[Image:Fundulopanchax gardneri.png|thumb|240px|Blue lyretail, ''Fundulopanchax gardneri'', one of the most common West African species of killifish kept in aquariums]] Many killifish are lavishly coloured and most species are easy to keep and breed in an aquarium. Specimens can be obtained from specialist societies and associations. Striped panchax (also known as the Golden Wonder killifish) are commonly found in pet shops, but caution must be exercised when considering tank mates, since the mouth of the Striped panchax is as wide as the head, and much smaller fish will be eaten. Flagfish, native to south Florida, is another species of killifish commonly found in pet stores. They are useful in aquariums for algae control. The golden topminnow (''Fundulus chrysotus'') is also native to the United States and often available at auction, but care must be taken with these fish to stop them from jumping out of the tank. A firm cover and a layer of floating plants is best when keeping these fish.{{cn|date=March 2026}}
In the 1960s, the American toy company Wham-O sold African killifish eggs, marketed as "instant fish", to be hatched in aquariums.<ref>{{Cite web |last=Toohey |first=Ellsworth |date=2024-12-16 |title=How African killifish almost became Wham-O's coolest toy of the 1960s |url=https://boingboing.net/2024/12/16/how-african-killifish-almost-became-wham-os-coolest-toy-of-the-1960s.html |access-date=2026-03-22 |website=Boing Boing |language=en-US}}</ref>
==Behaviour-altering infection== Normally, killifish avoid near-surface water to reduce the danger of being eaten by predators. However, when infected with a type of fluke the fish swim near the surface, and sometimes even swim upside down, exposing their camouflaged bellies. The fluke completes its lifecycle in the digestive tract of birds.<ref>{{Cite web |url=http://ngm.nationalgeographic.com/2014/11/mindsuckers/zimmer-text |title=Mindsuckers - National Geographic Magazine |access-date=2016-04-26 |archive-date=2016-04-26 |archive-url=https://web.archive.org/web/20160426031146/http://ngm.nationalgeographic.com/2014/11/mindsuckers/zimmer-text }}</ref>
==Evolved resistance to extreme levels of toxicity== The large populations of killifish and the genetic diversity of the species have enabled it to evolve and survive in areas where other species have died out, including Superfund sites. Over a few dozen generations of killifish<ref name="Yan">{{cite journal |last1=Yan |first1=Wudan |title=Pollution evolution: The little fish that could |journal=Knowable Magazine |publisher= Annual Reviews |date=23 April 2020 |doi=10.1146/knowable-042220-1 |s2cid=219039865 |doi-access=free |url=https://knowablemagazine.org/article/living-world/2020/killifish-pollution |access-date=4 April 2022 |language=en}}</ref><ref name="Cherr">{{cite journal |last1=Cherr |first1=Gary N. |last2=Fairbairn |first2=Elise |last3=Whitehead |first3=Andrew |title=Impacts of Petroleum-Derived Pollutants on Fish Development |journal=Annual Review of Animal Biosciences |date=8 February 2017 |volume=5 |issue=1 |pages=185–203 |doi=10.1146/annurev-animal-022516-022928 |pmid=27959669 |issn=2165-8102|doi-access=free }}</ref> in a relatively short period of time (50–60 years), killifish have evolved resistance against levels of dioxins, PCBs, mercury, and other industrial chemicals up to 8,000 times higher than the previously estimated lethal dose. Sequencing the genomes of the adapted individuals showed a common set of mutations among the pollution-tolerant fish, many of which help to deactivate or turn off a molecular pathway responsible for a large part of the cellular damage caused by the chemicals.<ref name="Konkel">{{cite web|last1=Konkel|first1=Lindsey|title=These Fish Evolved to Live in Extremely Toxic Water|url=http://news.nationalgeographic.com/2016/12/pollution-tolerant-killifish-discovered-east-coast-waters/|archive-url=https://web.archive.org/web/20161210140944/http://news.nationalgeographic.com/2016/12/pollution-tolerant-killifish-discovered-east-coast-waters/|archive-date=December 10, 2016|website=National Geographic|publisher=University of California, Davis|date=8 December 2016}}</ref>
Killifish were found to fare relatively well in the wake of the Deepwater Horizon oil spill.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2017/03/170313160821.htm |title=After Deepwater Horizon spill: Which animals weathered the disaster |date=March 13, 2017 |website=www.sciencedaily.com |publisher=Rutgers University |access-date=March 15, 2017}}</ref><ref name="McCann">{{cite journal |last1=McCann |first1=Michael J |last2=Able |first2=Kenneth W |last3=Christian |first3=Robert R |last4=Fodrie |first4=F Joel |last5=Jensen |first5=Olaf P |last6=Johnson |first6=Jessica J |last7=López-Duarte |first7=Paola C |last8=Martin |first8=Charles W |last9=Olin |first9=Jill A |last10=Polito |first10=Michael J |last11=Roberts |first11=Brian J |last12=Ziegler |first12=Shelby L |title=Key taxa in food web responses to stressors: the Deepwater Horizon oil spill |journal=Frontiers in Ecology and the Environment |date=April 2017 |volume=15 |issue=3 |pages=142–149 |doi=10.1002/fee.1474 |bibcode=2017FrEE...15..142M }}</ref>
The resistance of killifish to environmental changes, including toxicity, appears to be a longstanding adaptation of theirs. Abundant fossils of the extinct Miocene-aged killifish ''Kenyaichthys'' have been recovered from a prehistoric lake of the Lukeino Formation where few other fish fossils have been found. It has been suggested that this lake was subject to frequent flash droughts and increased heavy metal load from a nearby volcano. The ''Kenyaichthys'' fossils show evidence of deformities as a result of this metal load, but were still successful inhabitants of the lake.<ref>{{Cite journal |last1=Altner |first1=Melanie |last2=Reichenbacher |first2=Bettina |date=2015-04-29 |title=†Kenyaichthyidae fam. nov. and †Kenyaichthys gen. nov. – First Record of a Fossil Aplocheiloid Killifish (Teleostei, Cyprinodontiformes) |journal=PLOS ONE |language=en |volume=10 |issue=4 |article-number=e0123056 |doi=10.1371/journal.pone.0123056 |doi-access=free |issn=1932-6203 |pmc=4414574 |pmid=25923654|bibcode=2015PLoSO..1023056A }}</ref>
==References== {{Reflist}}
== External links == * the killi net – [http://img.kil.palo-alto.ca.us/ Database of killifish names, codes and pictures online since 1996] * Huber, J. (2021). [http://www.killi-data.org Killi-Data online] * [http://www.aka.org American Killifish Association, the first killi organisation of any sort] (AKA) * [https://killis.org.uk/ British Killifish Association, formed in 1965] (BKA) * Itrainsfishes – [http://www.itrainsfishes.net/ All about South American Killifishes] * [http://www.mangrove.org/taylor/ Rare Hermaphroditic Fish Survives in Mangrove Swamps] – D. Scott Taylor, Ph.D – mangrove.org * [https://www.nytimes.com/2015/03/03/science/in-short-lived-fish-secrets-to-aging.html In Short-Lived Fish, Secrets to Aging] – Carl Zimmer, New York Times
Category:Cyprinodontiformes Category:Fish common names