View source for Mummichog

{{Short description|Species of fish}}
{{speciesbox
 | status              = LC
 | status_system       = IUCN3.1
 | status_ref          = <ref name="iucn status 19 November 2021">{{cite iucn |author=NatureServe |date=2013 |title=''Fundulus heteroclitus'' |volume=2013 |article-number=e.T189824A18236919 |doi=10.2305/IUCN.UK.2013-1.RLTS.T189824A18236919.en |access-date=19 November 2021}}</ref>
 | name                = Mummichog
 | image               = mummichog.jpg
 | taxon               = Fundulus heteroclitus
 | authority           = ([[Carl Linnaeus|Linnaeus]], [[12th edition of Systema Naturae|1766]])
 | synonyms            = 
*''Cobitis heteroclita'' <small>Linnaeus, 1766</small>
*''Cobitis macrolepidota'' <small>[[Johann Julius Walbaum|Walbaum]], 1792</small>
*''Fundulus mudfish'' <small>Lacepède, 1803</small>
*''Esox pisciculus'' <small>[[Samuel L. Mitchill|Mitchill]], 1815</small>
*''Esox pisculentus'' <small>Mitchill, 1815</small>
*''Fundulus antillarum'' <small>[[Henry Weed Fowler|Fowler]], 1916</small>
*''Fundulus badius'' <small>[[Samuel Garman|Garman]], 1895</small>
*''Fundulus coenicolus'' <small>([[Marcus Elieser Bloch|Bloch]] & [[Johann Gottlob Theaenus Schneider|Schneider]], 1801)</small>
*''Fundulus fasciatus'' <small>(Bloch & Schneider, 1801)</small>
*''Fundulus fonticola'' <small>[[Achille Valenciennes|Valenciennes]], 1846</small>
*''Fundulus lozanoi'' <small>(Gomez Caruana ''et al.'', 1984)</small>
*''Fundulus nigrofaciatus'' <small>([[Charles Alexandre Lesueur|Lesueur]], 1817)</small>
*''Fundulus nisorius'' <small>[[Edward Drinker Cope|Cope]], 1870</small>
*''Fundulus ornatus'' <small>(Lesueur, 1817)</small>
*''Fundulus pisciculus'' <small>(Mitchill, 1815)</small>
*''Fundulus swampinus'' <small>([[Bernard Germain de Lacépède|Lacepède]], 1803)</small>
*''Fundulus vinctus'' <small>[[David Starr Jordan|Jordan]] & [[Charles Henry Gilbert|Gilbert]], 1882</small>
*''Fundulus viridescens'' <small>[[James Ellsworth De Kay|DeKay]], 1842</small>
*''Fundulus zebra'' <small>DeKay, 1842</small>
*''Hydargira nigrofaciata'' <small>Lesueur, 1817</small>
*''Hydrargira ornata'' <small>Lesueur, 1817</small>
*''Hydrargira swampina'' <small>Lacepède, 1803</small>
*''Poecilia coenicola'' <small>Bloch & Schneider, 1801</small>
*''Poecilia fasciata'' <small>Bloch & Schneider, 1801</small>
*''Valencia lozanoi'' <small>Gomez Caruana ''et al.'', 1984</small>
 | synonyms_ref        = <ref>{{Cite WoRMS |author=Nicolas Bailly |year=2014 |title=''Fundulus heteroclitus heteroclitus'' (Linnaeus, 1766) |db=FishBase |id=293599 |accessdate=March 12, 2015}}</ref><ref>{{Cite WoRMS |author=Nicolas Bailly |year=2014 |title=''Fundulus heteroclitus macrolepidotus'' (Walbaum, 1792) |db=FishBase |id=293600 |accessdate=March 12, 2015}}</ref><ref name = CofFA>{{Cof genus|genus=Fundulus|access-date=24 September 2019}}</ref>
}}

The '''mummichog''' ('''''Fundulus heteroclitus''''') is a small [[killifish]] found along the Atlantic coast of the [[United States]] and [[Canada]]. Also known as '''Atlantic killifish''', '''mummies''', '''gudgeons''', and '''mud minnows''', these fish inhabit [[brackish]] and [[coastal]] waters including [[estuaries]] and [[salt marsh]]es. The species is noted for its hardiness and ability to tolerate highly variable [[salinity]], temperature fluctuations from {{convert|6|to|35|C|F}}, very low oxygen levels (down to 1&nbsp;mg/L), and heavily polluted ecosystems. As a result, the mummichog is a popular research subject in [[embryological]], physiological, and [[toxicological]] studies. It is also the first fish ever sent to space, aboard [[Skylab]] in 1973.

==Taxonomy==
The genus name ''[[Fundulus]]'' comes from ''{{lang|la|[[:wikt:fundus|fundus]]}}'', meaning bottom, from the fish's habit of swimming near muddy bottoms. The species name ''heteroclitus'' means irregular or unusual. The [[type specimen]] was first described by [[Carl Linnaeus]] in 1766, from near [[Charleston, South Carolina]]. Other scientific names now considered [[Synonym (taxonomy)|synonyms]] for this species include ''Cobitis heteroclita'', ''Fundulus fasciatus'', ''Fundulus pisculentus'', and ''Fundulus nigrofasciatus''.<ref name="Scott">Scott, W.B., and Crossman, E.J. 1973. Freshwater fishes of Canada. Bulletin 184 of the Fisheries Research Board of Canada, Ottawa.</ref> The mummichog belongs to the order [[Cyprinodontiformes]], and the family Fundulidae. There are two [[subspecies]]: ''F. h. heteroclitus'' (Linnaeus, 1766), in the south and ''F. h. macrolepidotus'' (Walbaum, 1792) in the north. As ''F. mudfish'' this species was designated the [[type species]] of ''Fundulus'' when [[Bernard Germain de Lacépède|Lacépède]] created the genus in 1803.<ref name = CofFG>{{Cof record|genid=535|title=''Fundulus''|access-date=24 September 2019}}</ref>

The name mummichog is derived from a [[Narragansett people|Narragansett]] term meaning "going in crowds", which reflects the mummichog's strong shoaling tendency.<ref>"Mummichog." Merriam-Webster.com. Merriam-Webster, n.d. Web. 6 February 2014. http://www.merriam-webster.com/dictionary/mummichog</ref> Colloquial names include mummy, killie, kelley, chub, salt water minnow, mud minnow, mud dabbler, marsh minnow, brackish water chub, gudgeon, and common killifish. Some of these terms may lead to confusion: the term minnow should be reserved for species of the family [[Cyprinidae]], the mudminnows are members of the family [[Umbridae]], and the name [[gudgeon (fish)|gudgeon]] is used for various bottom-dwelling species of [[Cyprinidae|cyprinid]], [[Eleotridae|eleotrid]], and [[Dartfish|ptereleotrid]] fishes, none of which belongs to the same family as the fundulid mummichog.<ref name="Helfman">Helfman, G.S., Collette, B.B., Facey, D.E., and Boweb, B.W. 2009. The Diversity of Fishes, 2nd ed. Wiley-Blackwell,Oxford.</ref>

==Description==
[[File:Fundulus heteroclitus.jpg|thumb|Mummichog at [[Saint Michaels, Maryland|Saint Michaels]], [[Chesapeake Bay]], United States]]
The body of the mummichog is elongate but thick, with a deep caudal peduncle. Usual length is {{convert|7.5|to|9|cm|in|abbr=on}} but a maximum length of up to {{convert|15|cm|in|abbr=on}} is possible. The mouth is upturned and the lower jaw protrudes when the mouth is closed. Pectoral and tail fins are round. Mummichogs have 10–13 dorsal fin rays, 9–12 anal fin rays and 16–20 pectoral fin rays. Males have larger dorsal and anal fins than females. There is no [[lateral line]] on the body, but lateral line pores are present on the head. The colour is variable (and may even change in shade within the same individual when placed near different backgrounds)<ref>Connolly, C.J. 1925. Adaptive changes in shades and color of ''Fundulus''. Biological Bulletin (Woods Hole) 48: 56–77.</ref><ref>Bagnara, J.T., and Hadley, M.E. 1973. Chromatophores and color change. Prentice-Hall, New Jersey.</ref> but is generally olive-brown or olive-green. There can be vertical bars on the sides that are thin, wavy, and silvery. Colors are more intense in males during the reproductive season, as they become dark olive-green on the back, steel-blue on the sides with about 15 silvery bars, and yellow or orange-yellow on the underside; the dorsal fin is mottled and a small [[eyespot (mimicry)|eyespot]] may be present near the rear edge. Females tend to be paler, without bars or the intense yellow on the belly, and their dorsal fin is uniformly coloured.{{Citation needed|date=April 2021}}

Adults of the two subspecies can be distinguished based on slight morphological<ref name="Able, K.W. 1986">{{cite journal | last1 = Able | first1 = K.W. | last2 = Felley | first2 = J.D. | year = 1986 | title = Geographical variation in ''Fundulus heteroclitus'': tests for concordance between egg and adult morphologies | journal = American Zoologist | volume = 26 | pages = 145–157 | doi=10.1093/icb/26.1.145| doi-access = free }}</ref> and genomic<ref name="Brown, B.L. 1991">{{cite journal | last1 = Brown | first1 = B.L. | last2 = Chapman | first2 = R.W. | year = 1991 | title = Gene flow and mitochondrial DNA variation in the killifish, ''Fundulus heteroclitus'' | journal = Evolution | volume = 45 | issue = 5| pages = 1147–1161 | doi=10.2307/2409722| pmid = 28564171 | jstor = 2409722 }}</ref> differences. Further, eggs of the northern subspecies have filaments (adhesive chorionic fibrils) that eggs of the southern subspecies lack. While the northern subspecies deposits eggs in the sand, the southern subspecies often deposits eggs inside empty mussel shells.<ref name="Coad">Coad, B.W. 1995. Encyclopedia of Canadian Fishes. Canadian Museum of Nature, Ottawa, 928p.</ref><ref name="Taylor, M.H. 1986">{{cite journal | last1 = Taylor | first1 = M.H. | year = 1986 | title = Environmental and endocrine influences on reproduction of ''Fundulus heteroclitus'' | journal = American Zoologist | volume = 26 | pages = 159–171 | doi=10.1093/icb/26.1.159| doi-access = free }}</ref>

The mummichog is very similar to the [[banded killifish]], ''Fundulus diaphanus'', and indeed the two species have been known to interbreed.<ref>Hubbs, C.L., Walker, B.W., and Johnson, R.E. 1943. Hybridization in nature between species of American cyprinodont fishes. ''Contributions to the Laboratory of Vertebrate Biology of the University of Michigan'' 23: 21 p.</ref> The two species may overlap in their choice of habitat, but in general the banded killifish is more commonly found in freshwater, which is not the case for the mummichog. The banded killifish tends to have thin dark bars on a light side, whereas in the mummichog the bars are thin and light on a dark side. Internally, the banded killifish has 4–7 [[gill raker]]s, as opposed to 8–12 in the mummichog.{{Citation needed|date=April 2021}}

==Distribution and habitat==

This species ranges along the Atlantic coast of North America, from [[Gaspé Peninsula]], [[Anticosti Island]] and [[Port au Port Bay]] in the north to northeastern [[Florida]] in the south. It is present on [[Sable Island]], {{convert|175|km|mi|abbr=on}} southeast of the closest point of mainland [[Nova Scotia]] in the Atlantic Ocean.<ref>{{cite journal| last1 = Garside | first1 = E.T. | year = 1969 | title = Distribution of insular fishes of Sable Island, Nova Scotia | journal = Journal of the Fisheries Research Board of Canada | volume = 26 | issue = 5| pages = 1390–1392 | doi=10.1139/f69-126}}</ref> The approximate geographical division between the two subspecies lies in [[New Jersey]], [[Delaware]] and [[Virginia]].{{Citation needed|date=April 2021}}

[[Introduced species|Introduced]] populations have become established on the Atlantic coast of Portugal and southwestern Spain, starting in the 1970s<ref>Hernando, J.A., 1975. Nuevas localidades de ''Valencia hispanica'' (Pisces: Ciprinodontidae) en el Suroeste de España. Doñana Acta Vertebrata 2: 265–267.</ref><ref>{{cite journal | last1 = Coelho | first1 = M. | last2 = Gomes | first2 = J. | last3 = Ré | first3 = P.B. | year = 1976 | title = ''Valencia hispanica'', a new fish to Portugal | journal = Arquivos do Museu Bocage | volume = 6 | pages = 1–3 }}</ref><ref>{{cite journal | last1 = Gutiérrez-Estrada | first1 = J.C. | last2 = Prenda | first2 = J. | last3 = Oliva | first3 = F | last4 = Fernandez-Delgado | first4 = C. | year = 1998 | title = Distribution and habitat preferences of the introduced mummichog ''Fundulus heteroclitus'' (Linneaus) [''sic''] in South-western Spain | url = http://rabida.uhu.es/dspace/bitstream/10272/4178/2/distribution_%20habitat_preferences_%20introduced_%20mummichog_%20fundulus_%20heteroclitus_%20southwestern_%20spain.pdf| journal = Estuarine, Coastal and Shelf Science | volume = 46 | issue = 6| pages = 827–835 | doi=10.1006/ecss.1997.0318| bibcode = 1998ECSS...46..827G | hdl = 10272/4178 | hdl-access = free }}</ref> and some have now reached the western Mediterranean basin.<ref>{{cite journal | last1 = Gisbert | first1 = E. | last2 = Lopez | first2 = M.A. | year = 2007 | title = First record of a population of the exotic mummichog, ''Fundulus heteroclitus'' (L., 1766) in the Mediterranean Sea basin (Ebro River delta) | journal = Journal of Fish Biology | volume = 71 | issue = 4| pages = 1220–1224 | doi=10.1111/j.1095-8649.2007.01579.x| bibcode = 2007JFBio..71.1220G }}</ref> There may also be introduced populations in Hawaii and the Philippines.<ref>Fish Base [http://www.fishbase.org/Introductions/IntroductionsList.php?ID=3192&GenusName=Fundulus&SpeciesName=heteroclitus&fc=570&StockCode=3388 Mummichog distribution]</ref> As bait fish, mummichogs are sometimes released in freshwater habitats, where they can survive, and there have been reports of individuals in [[New Hampshire]] ponds, as well as the upper [[Ohio River]] and [[Beaver River (Pennsylvania)|Beaver River]].<ref>USGS Nonindigenous aquatic species database [https://nas2.er.usgs.gov/viewer/omap.aspx?SpeciesID=688 Mummichog occurrences]</ref>

The mummichog is a common fish in coastal habitats such as salt marshes, muddy creeks, tidal channels, brackish estuaries, [[Zostera|eelgrass]] or [[Spartina|cordgrass]] beds, and sheltered shorelines. It can be found within coastal rivers but seldom beyond the [[head of tide]]. A few landlocked populations may exist in freshwater lakes close to shore, for example on [[Digby Neck]], Nova Scotia.<ref>{{cite journal | last1 = Klawe | first1 = W.L. | year = 1957 | title = Common mummichog and newt in a lake on Digby Neck, Nova Scotia | journal = Canadian Field-Naturalist | volume = 71 | issue = 3 | pages = 154–155 | doi = 10.5962/p.341724 | doi-access = free }}</ref>

==Diet==
Mummichogs are agastric [[omnivorous|omnivores]].<ref>{{Cite journal |last1=Wood |first1=Chris M. |last2=Bucking |first2=Carol |last3=Grosell |first3=Martin |date=2010-08-01 |title=Acid–base responses to feeding and intestinal Cl– uptake in freshwater- and seawater-acclimated killifish,''Fundulus heteroclitus'', an agastric euryhaline teleost |journal=Journal of Experimental Biology |volume=213 |issue=15 |pages=2681–2692 |doi=10.1242/jeb.039164 |pmid=20639430 |bibcode=2010JExpB.213.2681W |issn=1477-9145|doi-access=free }}</ref> Analyses of their gut contents have found diatoms, amphipods and other crustaceans, molluscs, fish eggs (including their own species), very small fish, insect larvae, and bits of eelgrass.<ref name="Scott"/>

==Physiology==
This fish is well known for its ability to withstand a variety of environmental conditions.<ref>{{cite journal | last1 = Burnett | first1 = K.G. | last2 = Bain | first2 = L.J. | last3 = Baldwin | first3 = D.S. | display-authors = etal   | year = 2007 | title = ''Fundulus'' as the premier teleost model in environmental biology: Opportunities for new insights using genomics | journal = Comparative Biochemistry and Physiology D | volume = 2 | issue = 4| pages = 257–266 | doi=10.1016/j.cbd.2007.09.001| pmid = 18071578 | pmc = 2128618 }}</ref> They can survive temperatures between {{convert|6|and(-)|35|C|F}}; even within the same [[tidal cycle]] they can tolerate rapid temperature changes from {{convert|15|to(-)|30|C|F}}.<ref name="Abraham">Abraham, B.J. 1985. Species Profiles: Life histories and environmental requirements of coastal fishes and invertebrates (Mid-Atlantic)--mummichog and striped killifish. U.S. Fish and Wildlife Service Biological Reports 82 (11.40): 23 p. https://www.nwrc.usgs.gov/wdb/pub/species_profiles/82_11-040.pdf</ref> They are able to survive this vast temperature range by altering their metabolic rates at high and low temperatures. This is partly achieved by varying the isoenzyme of the lactate dehydrogenase ([[Lactate dehydrogenase b|Ldh-B]]) enzyme expressed in warm or cold waters. These two versions of the enzyme allow for faster catalytic function and metabolism depending on if the fish is in northern, colder waters or southern, warmer waters.<ref>{{Cite journal|last1=Mitton|first1=Jeffry B|last2=Koehn|first2=Richard K|title=Genetic Organization and Adaptive Response of Allozymes to Ecological Variables in Fundulus Heteroclitus |date=1975-01-01|journal=Genetics|volume=79|issue=1|pages=97–111|doi=10.1093/genetics/79.1.97|pmid=1126624 |pmc=1213263 |issn=1943-2631}}</ref> Based on genetic studies, the enzymes serum [[esterase]] (SERE) and malate dehydrogenase [[Malate dehydrogenase|(MDH]]) also appear to play an important role in mummichog temperature control.<ref>{{Cite journal|last1=Powers|first1=Dennis A.|last2=Schulte|first2=Patricia M.|date=September 1998|title=Evolutionary adaptations of gene structure and expression in natural populations in relation to a changing environment: A multidisciplinary approach to address the million-year saga of a small fish|journal=The Journal of Experimental Zoology|volume=282|issue=1–2|pages=71–94|doi=10.1002/(sici)1097-010x(199809/10)282:1/2<71::aid-jez11>3.0.co;2-j|pmid=9723168 |issn=0022-104X}}</ref>

They are also among fish species most tolerant of salinity changes ([[euryhaline]]).<ref>{{cite journal | last1 = Whitehead | first1 = A | year = 2010 | title = The evolutionary radiation of diverse osmotolerant physiologies in killifish (''Fundulus'' sp.) | journal = Evolution | volume = 64 | issue = 7| pages = 2070–2085 | doi=10.1111/j.1558-5646.2010.00957.x | pmid=20100216| s2cid = 23354536 | doi-access =  }}</ref> Mummichog larvae can grow in salinities ranging from 0.4 to 100 parts per thousand, the latter being about three times the normal salinity of seawater. Adult mummichogs tolerate low oxygen levels down to 1&nbsp;mg/L, at which they resort to [[hypoxia in fish|aquatic surface respiration]] (breathing in the surface layer of water, richer in oxygen because of contact with air) to survive.<ref>{{cite journal | last1 = Wannamaker | first1 = C.M. | last2 = Rice | first2 = J.A. | year = 2000 | title = Effects of hypoxia on movements and behavior of selected estuarine organisms from the southeastern United States | journal = Journal of Experimental Marine Biology and Ecology | volume = 249 | issue = 2| pages = 145–163 | doi=10.1016/s0022-0981(00)00160-x| pmid = 10841932 | bibcode = 2000JEMBE.249..145W }}</ref><ref>{{cite journal | last1 = Stierhoff | first1 = K.L. | last2 = Targett | first2 = T.E. | last3 = Grecay | first3 = P.A. | year = 2003 | title = Hypoxia tolerance of the mummichog: the role of access to the water surface | journal = Journal of Fish Biology | volume = 63 | issue = 3| pages = 580–592 | doi=10.1046/j.1095-8649.2003.00172.x| bibcode = 2003JFBio..63..580S }}</ref> They can even survive for a few hours in moist air outside of water, breathing air directly.<ref>{{cite journal | last1 = Halpin | first1 = P.M. | last2 = Martin | first2 = K.L.M. | year = 1999 | title = Aerial respiration in the salt marsh fish ''Fundulus heteroclitus'' (Fundulidae) | journal = Copeia | volume = 1999 | issue = 3| pages = 743–748 | doi=10.2307/1447607| jstor = 1447607 }}</ref>

Populations have developed resistance to [[methylmercury]], [[kepone]], [[dioxins and dioxin-like compounds|dioxins]], [[polychlorinated biphenyl]], and [[polyaromatic hydrocarbons]].<ref>{{cite journal | last1 = Weis | first1 = J | year = 2002 | title = Tolerance to environmental contaminants in the mummichog, ''Fundulus heteroclitus'' | journal = Human and Ecological Risk Assessment | volume = 8 | issue = 5| pages = 933–953 | doi=10.1080/1080-700291905756| bibcode = 2002HERA....8..933W | s2cid = 85361429 }}</ref> One study<ref>{{cite journal | last1 = Whitehead | first1 = A. | last2 = Galvez | first2 = F. | last3 = Zhang | first3 = S. | last4 = Williams | first4 = L.M. | last5 = Oleksiak | first5 = M.F. | year = 2011 | title = Functional genomics of physiological plasticity and local adaptation in killifish | journal = Journal of Heredity | volume = 102 | issue = 5| pages = 499–511 | doi = 10.1093/jhered/esq077 | pmid=20581107 | pmc=3156563}}</ref> has looked at the genomic variation exhibited by mummichogs populations living in [[Newark Bay]], [[Acushnet River|New Bedford Harbor]], and the [[Elizabeth River (Virginia)]] (in some areas heavily polluted with polychlorinated biphenyls and [[creosote]], a complex mixture containing dioxin-like chemicals) and has found that about 20% of their genes were modified as compared to populations living in clean sites.

==Behavior==
Mummichogs live in dense shoals that can include several hundred individuals.{{Citation needed|date=April 2021}}

During cold winter months in the northern parts of their range, mummichogs move to upstream tidal pools, where they burrow into the mud at depths up to {{convert|20|cm|in|abbr=on}} to overwinter.<ref>{{cite journal| last1 = Chidester | first1 = F.E. | year = 1920 | title = The behavior of ''Fundulus heteroclitus'' in the salt marshes of New Jersey | journal = American Naturalist | volume = 54 | issue = 635| pages = 244–245 | doi=10.1086/279787| bibcode = 1920ANat...54..551C | s2cid = 83738153 }}</ref><ref>{{cite journal | last1 = Raposa | first1 = K | year = 2003 | title = Overwintering habitat selection by the mummichog, ''Fundulus heteroclitus'', in a Cape Cod (USA) salt marsh | journal = Wetlands Ecology and Management | volume = 11 | issue = 3| pages = 175–182 | doi = 10.1023/A:1024244317173 | bibcode = 2003WetEM..11..175R | s2cid = 27058471 }}</ref> They can also bury themselves in mud if they are caught in a drying tidal pool between [[spring tide]]s. Alternatively, they can travel short distances on land to get back to the sea.<ref>{{cite journal | last1 = Mast | first1 = S. O. | year = 1915 | title = The behavior of ''Fundulus'', with especial reference to overland escape from tide-pools and locomotion on land | url =https://zenodo.org/record/1429177 | journal = Journal of Animal Behavior | volume = 5 | issue = 5| pages = 341–350 | doi = 10.1037/h0075747 }}</ref>

In the laboratory, mummichogs have yielded clear examples of free-running [[circadian rhythms]], in both body colour<ref>{{cite journal| last1 = Kavaliers | first1 = M. | last2 = Abbott | first2 = F.S. | year = 1977 | title = Rhythmic colour change of the killifish, ''Fundulus heteroclitus'' | journal = Canadian Journal of Zoology | volume = 55 | issue = 3| pages = 553–561 | doi=10.1139/z77-070 | bibcode = 1977CaJZ...55..553K }}</ref> and swimming activity.<ref>{{cite journal| last1 = Kavaliers | first1 = M. | year = 1980 | title = Social groupings and circadian activity of the killifish, ''Fundulus heteroclitus'' | journal = Biological Bulletin | volume = 158 | issue = 1| pages = 69–76 | doi=10.2307/1540759| jstor = 1540759 | url = https://www.biodiversitylibrary.org/part/6319 }}</ref> For the latter, clear rhythms were obtained in single individuals as well as in groups of 5 or 25 individuals. Evidence of free-running semi-lunar rhythms have also been obtained in mummichogs: in constant laboratory conditions, egg production peaked every 14.8 days for up to 5 months.<ref>{{cite journal| last1 = Hsiao | first1 = S.-M. | last2 = Meier | first2 = A.H. |year = 1989 | title = Comparison of semilunar cycles of spawning activity in ''Fundulus grandis'' and ''F. heteroclitus'' held under constant laboratory conditions | journal = Journal of Experimental Zoology | volume = 252 | issue = 3| pages = 213–218 | doi=10.1002/jez.1402520302 | bibcode = 1989JEZ...252..213H }}</ref>

===Reproduction===
Spawning takes place from spring through fall. In the southernmost populations, up to eight spawnings are possible in a season. Spawning takes place most often at high tide and when the moon is new or full. Maximal spawning occurs when high [[spring tide]]s coincide with night,<ref>{{cite journal | last1 = Taylor | first1 = M.H. | last2 = Leach | first2 = G.J. | last3 = DiMichele | first3 = L. | last4 = Levithan | first4 = W.H. | last5 = Jacob | first5 = W.F. | year = 1979 | title = Lunar spawning cycle in the mummichog, ''Fundulus Heteroclitus'' (Pisces: Cyprinodontidae) | journal = Copeia | volume = 1979 | issue = 2| pages = 291–297 | doi=10.2307/1443417| jstor = 1443417 }}</ref> though spawning during the day remains possible.{{Citation needed|date=April 2021}}

During courtship, males may pursue females, and females may attract males by turning on their sides near the bottom and flicking their tails. A male and female may swim together for a while, after which the male crowds the female against a rock or a plant and clasps her: the male's larger dorsal and anal fins curve around the female's body. Fingerlike projections that develop on the male's scales behind and below the dorsal fin may help the male maintain contact with the female. The pair quivers vigorously and eggs and sperm are released.<ref>{{cite journal | last1 = Newman | first1 = H.H. | year = 1907 | title = Spawning behavior and sexual dimorphism in ''Fundulus heteroclitus'' and allied fish | journal = Biological Bulletin (Woods Hole) | volume = 12 | issue = 5| pages = 314–345 | doi=10.2307/1535681| jstor = 1535681 }}</ref>

The eggs are pale yellow, about {{convert|2|mm|in|abbr=on|2}} in diameter, and strongly adhesive. During a spawning event, a female can deposit up to 740 eggs in separate clutches of 10 to 300 eggs at a time.<ref name="Coad"/> The eggs adhere to plants, algal mats, empty mussel shells, sand, or mud at sites that are reached by water only at high spring tides.<ref name="Coad"/> Eggs therefore develop while exposed to moist air, and they hatch when the next high spring tides reach them.<ref>Taylor, M.H., DiMichele, L., and Leach, G.J. 1977. Egg stranding in the life cycle of the mummichog ''Fundulus heteroclitus''. Copeia: 1977: 397–399.</ref><ref>{{cite journal | last1 = Taylor | first1 = M.H. | last2 = DiMichele | first2 = L. | year = 1983 | title = Spawning site utilization in a Delaware population of ''Fundulus heteroclitus'' (Pisces: Cyprinodontidae) | journal = Copeia | volume = 1983 | issue = 3| pages = 719–725 | doi=10.2307/1444338| jstor = 1444338 }}</ref><ref>{{cite journal | last1 = Taylor | first1 = M.H. | year = 1999 | title = A suite of adaptations for intertidal spawning | journal = American Zoologist | volume = 39 | issue = 2| pages = 313–320 | doi=10.1093/icb/39.2.313| doi-access = free }}</ref> The eggs cannot hatch in air, nor can they do so in moving water; hatching is initiated by a lack of oxygen, something that can happen in the boundary layer of relatively still water surrounding the metabolically active egg at high tide, but not in air or in moving water.<ref>{{cite journal | last1 = DiMichele | first1 = L. | last2 = Powers | first2 = D.A. | year = 1984 | title = The relationship between oxygen consumption rate and hatching in ''Fundulus heteroclitus'' | journal = Physiological Zoology | volume = 57 | pages = 46–51 | doi=10.1086/physzool.57.1.30155966| s2cid = 87680036 }}</ref>

As opposed to their northern counterparts, the southern subspecies have eggs that lack filaments (adhesive chorionic fibrils)<ref>{{cite journal | last1 = Morin | first1 = R.P. | last2 = Able | first2 = K.W. | year = 1983 | title = Patterns of geographic variation in the egg morphology of the fundulid fish, ''Fundulus heteroclitus'' | journal = Copeia | volume = 1983 | issue = 3| pages = 726–740 | doi=10.2307/1444339| jstor = 1444339 }}</ref> and they often deposit those eggs inside empty mussel shells.<ref name="Coad"/><ref name="Taylor, M.H. 1986"/> The two subspecies are also distinguished based on slight morphological<ref name="Able, K.W. 1986"/> and genomic<ref name="Brown, B.L. 1991"/> differences.

Most mummichogs become sexually mature when two years old, around {{convert|3.8|cm|in|abbr=on}} in length. Normal lifespan is four years.<ref name="Coad"/>

==Parasites==

Mummichogs are hosts to a [[Parasitism|parasitic]] fluke, ''[[Homalometron pallidum]]'', which has a complex lifecycle involving the aquatic snail, ''[[Ecrobia truncata]]''.<ref>{{cite journal |author=Stunkard, Horace W. |year=1964 |title=The morphology, life history and systematics of the digenetic trematode ''Homalometron pallidum'' Stafford 1904 |journal=The Biological Bulletin |volume=126 |issue=1 |pages=163–173 |url=http://www.biolbull.org/content/126/1/163.full.pdf |doi=10.2307/1539426|jstor=1539426 }}</ref> Other parasite species reported in mummichogs include 10 protozoans, eight trematodes, one nematode, two acanthocephalans, and two crustaceans.<ref>Hoffman, G.L. 1967. Parasites of North American freshwater fishes. University of California Press, Berkeley, 486 pp.</ref>  A study in New Jersey found that mummichogs heavily infested with the digenean gill parasite ''Ascocotyle phagicola'', spent more time near the surface and exhibited conspicuous behaviors such as jerking, an example of a parasite affecting the behavior of its host in a way beneficial to the parasite, as conspicuous behaviors near the surface make the fish more likely to be noticed by predatory wading birds, the next host in the parasite's life cycle.<ref>{{cite journal | last1 = Santiago Bass | first1 = C. | last2 = Weis | first2 = J.S. | year = 2009 | title = Conspicuous behaviour of ''Fundulus heteroclitus'' associated with high digenean metacercariae gill abundances | journal = Journal of Fish Biology | volume = 74 | issue = 4| pages = 763–772 | doi=10.1111/j.1095-8649.2008.02148.x| pmid = 20735598 | bibcode = 2009JFBio..74..763S }}</ref>

==Interest to humans==
Mummichogs readily eat mosquito larvae and attempts have been made to use them as [[Biological pest control|biocontrol]] agents of mosquito populations.<ref name="Abraham"/>

===Fishing===
Mummichogs are sold as bait in sport fisheries for marine species such as [[summer flounder]], [[striped bass]] and [[bluefish]], or even sometimes for freshwater species.<ref name="Abraham"/> They are the most popular baitfish species in the Northeast of America and traditionally when used as bait they were lip hooked and then dressed with a piece of squid.<ref>{{cite journal |last1=Saccente |first1=Frank |title=Workhorse Bait |journal=Angler's Journal |volume=4 |issue=1 |page=38}}</ref>

===Scientific utility===

Mummichogs are considered an important environmental [[model organism]] because of their ability to tolerate various extremes of chemical ([[pollution]], etc.) and physical (temperature, [[salinity]], oxygen, etc.) conditions. They are relatively abundant in nature and can be easily captured, transported and reared in laboratory facilities. They are commonly used in scientific studies of stress biology,<ref>{{Cite Q| Q34393031|author=Schulte, P.M.|author-link=Patricia Schulte}}</ref> thermal physiology and [[toxicology]], and have also been studied in the contexts of evolutionary biology, developmental biology, [[endocrinology]], cancer biology, and chronobiology (study of [[circadian rhythms]]).<ref>{{cite journal | last1 = Kavaliers | first1 = M | year = 1980 | title = Social groupings and circadian activity of the killifish, ''Fundulus heteroclitus'' | journal = Biological Bulletin | volume = 158 | issue = 1| pages = 69–76 | doi=10.2307/1540759| jstor = 1540759 | url = https://www.biodiversitylibrary.org/part/6319 }}</ref><ref>{{cite journal | last1 = Kavaliers | first1 = M. | last2 = Abbott | first2 = F.S. | year = 1977 | title = Rhythmic colour change of the killifish, ''Fundulus heteroclitus'' | journal = Canadian Journal of Zoology | volume = 55 | issue = 3| pages = 553–561 | doi=10.1139/z77-070 | bibcode = 1977CaJZ...55..553K }}</ref> With the successful sequencing and assembly of the full killifish genome,<ref>{{Cite web | url=https://www.ncbi.nlm.nih.gov/genome/ | archive-url=https://web.archive.org/web/20021229193132/http://www.ncbi.nlm.nih.gov/genome/ | archive-date=December 29, 2002 | title=Home - Genome - NCBI}}</ref> they serve as a premier scientific model for studying biochemical and physiological responses to varying environmental conditions.<ref>{{cite journal | last1 = Lister | first1 = AL | last2 = Van Der Kraak | first2 = GJ | last3 = Rutherford | first3 = R | last4 = MacLatchy | first4 = D | year = 2011 | title = ''Fundulus heteroclitus'': ovarian reproductive physiology and the impact of environmental contaminants | journal = Comparative Biochemistry and Physiology C | volume = 154 | issue = 4| pages = 278–287 | doi=10.1016/j.cbpc.2011.07.004| pmid = 21771666 }}</ref>

Their remarkable ability to tolerate various extremes of temperature and salinity has made them popular subjects in scientific studies of [[toxicology]]. For decades the killifish has been a useful laboratory model for toxicological studies that include exposures to single chemicals, chemical mixtures, and complex contaminated media.<ref name="Atz">{{Cite journal|last1=Atz|first1=J.W.|year=1986|title=Fundulus heteroclitus in the laboratory: A history|journal=American Zoologist|volume=26|pages=111–120|doi=10.1093/icb/26.1.111 |doi-access=free}}</ref> It is sometimes the only fish species found in severely polluted and oxygen-deprived waterways, such as the [[Elizabeth River (Virginia)|Elizabeth River]] in Virginia and, in New Jersey, the [[Hackensack River]] and the [[Arthur Kill]]. A 2008 [[Virginia Institute of Marine Science]] report stated that 38% of mummichogs from Elizabeth River had cancerous lesions, and "more than half had pre-cancerous lesions. That was largely due to high levels of [[polycyclic aromatic hydrocarbons]]".<ref>Rona Kobell [http://www.bayjournal.com/article/elizabeth_river_rises_from_the_depths Elizabeth River rises from the depths.Dedicated group is slowly bringing one of nation's most polluted rivers back to life.] Bay Journal, July 01, 2011</ref>

Killifish eggs are used in developmental studies and when teaching embryology because the eyes, the beating heart, and the different stages of [[ontogenesis]] can be easily examined. Embryos are also extremely durable and easy to manipulate in the laboratory.<ref name="Atz"/>

Mummichogs were the first fish sent to space.<ref>Reebs, S.G. (2009) [http://www.howfishbehave.ca/pdf/Fishes%20in%20space.pdf Fish in space] Retrieved 12 December 2014.</ref> In 1973 a couple of them were flown in a plastic bag aquarium aboard [[Skylab]], during the [[Skylab 3]] mission. In the absence of gravity the fish at first exhibited an unusual swimming behavior: they constantly pitched forward and therefore described tight circles. However, by day 22 of the mission they swam normally. Fifty eggs at an advanced stage of development had also been taken on board, and 48 of them hatched during the flight. The hatchlings swam normally.<ref>{{cite journal | last1 = Von Baumgarten | first1 = R.J. | last2 = Simmonds | first2 = R.C. | last3 = Boyd | first3 = J.F. | last4 = Garriott | first4 = O.K. | year = 1975 | title = Effects of prolonged weightlessness on the swimming pattern of fish aboard Skylab 3 | journal = Aviation, Space, and Environmental Medicine | volume = 46 | issue = 7 | pages = 902–906 | pmid = 1156300 }}</ref> More experiments with mummichogs in space followed as part of the [[Apollo–Soyuz Test Project]]<ref>{{cite journal | last1 = Hoffman | first1 = R.B. | last2 = Salinas | first2 = G.A. | last3 = Baky | first3 = A.A. | year = 1977 | title = Behavioral analyses of killifish exposed to weightlessness in the Apollo-Soyuz test project | journal = Aviation, Space, and Environmental Medicine | volume = 48 | issue = 8| pages = 712–717 | pmid = 889544 }}</ref> and as part of a biological package aboard the [[Bion 3|Bion 3/Kosmos 782]] satellite.<ref>NASA {{Cite web|url=http://lis.arc.nasa.gov/lis/Programs/Cosmos/Cosmos_782/Cosmos_782.html |archive-url=https://web.archive.org/web/20060929212656/http://lis.arc.nasa.gov/lis/Programs/Cosmos/Cosmos_782/Cosmos_782.html |archive-date=2006-09-29 |title=Bion 3 / Kosmos 782}}</ref>

== See also ==
* [[Japanese rice fish]] (''Oryzias latipes''), first fish to breed in space in 1994

==References==
{{Reflist|32em}}

==External links==
*{{Commons category-inline|Fundulus heteroclitus|''Fundulus heteroclitus''}}
* [http://www.fishbase.org/Summary/SpeciesSummary.php?id=3192 Fishbase entry (with image)]

{{Taxonbar|from=Q939303}}

[[Category:Fundulus]]
[[Category:Fish of the Western Atlantic]]
[[Category:Fish of the Eastern United States]]
[[Category:Fish of Canada]]
[[Category:Fauna of Atlantic Canada]]
[[Category:Fauna of the Northeastern United States]]
[[Category:Least concern biota of the United States]]
[[Category:Least concern biota of North America]]
[[Category:Fish described in 1766]]
[[Category:Animal taxa named by Carl Linnaeus]]