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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 . The species is noted for its hardiness and ability to tolerate highly variable salinity, temperature fluctuations from , very low oxygen levels (down to 1 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.
The name mummichog is derived from a Narragansett term meaning "going in crowds", which reflects the mummichog's strong shoaling tendency."Mummichog." Merriam-Webster.com. Merriam-Webster, n.d. Web. 6 February 2014. http://www.merriam-webster.com/dictionary/mummichog 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 is used for various bottom-dwelling species of Cyprinidae, Eleotridae, and Dartfish fishes, none of which belongs to the same family as the fundulid mummichog.Helfman, G.S., Collette, B.B., Facey, D.E., and Boweb, B.W. 2009. The Diversity of Fishes, 2nd ed. Wiley-Blackwell,Oxford.
Adults of the two subspecies can be distinguished based on slight morphological and genomic 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.Coad, B.W. 1995. Encyclopedia of Canadian Fishes. Canadian Museum of Nature, Ottawa, 928p.
The mummichog is very similar to the banded killifish, Fundulus diaphanus, and indeed the two species have been known to interbreed.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. 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 , as opposed to 8–12 in the mummichog.
Introduced populations have become established on the Atlantic coast of Portugal and southwestern Spain, starting in the 1970sHernando, J.A., 1975. Nuevas localidades de Valencia hispanica (Pisces: Ciprinodontidae) en el Suroeste de España. Doñana Acta Vertebrata 2: 265–267. and some have now reached the western Mediterranean basin. There may also be introduced populations in Hawaii and the Philippines.Fish Base Mummichog distribution 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.USGS Nonindigenous aquatic species database Mummichog occurrences
The mummichog is a common fish in coastal habitats such as salt marshes, muddy creeks, tidal channels, brackish estuaries, Zostera or Spartina 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.
They are also among fish species most tolerant of salinity changes (euryhaline). 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 mg/L, at which they resort to aquatic surface respiration (breathing in the surface layer of water, richer in oxygen because of contact with air) to survive. They can even survive for a few hours in moist air outside of water, breathing air directly.
Populations have developed resistance to methylmercury, kepone, dioxins, polychlorinated biphenyl, and polyaromatic hydrocarbons. One study has looked at the genomic variation exhibited by mummichogs populations living in Newark Bay, Acushnet River, 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.
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 to overwinter. They can also bury themselves in mud if they are caught in a drying tidal pool between . Alternatively, they can travel short distances on land to get back to the sea.
In the laboratory, mummichogs have yielded clear examples of free-running circadian rhythms, in both body colour and swimming activity. 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.
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.
The eggs are pale yellow, about 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. 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. Eggs therefore develop while exposed to moist air, and they hatch when the next high spring tides reach them.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. 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.
As opposed to their northern counterparts, the southern subspecies have eggs that lack filaments (adhesive chorionic fibrils) and they often deposit those eggs inside empty mussel shells. The two subspecies are also distinguished based on slight morphological and genomic differences.
Most mummichogs become sexually mature when two years old, around in length. Normal lifespan is four years.
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. It is sometimes the only fish species found in severely polluted and oxygen-deprived waterways, such as the 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".Rona Kobell 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
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.
Mummichogs were the first fish sent to space.Reebs, S.G. (2009) Fish in space Retrieved 12 December 2014. 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. More experiments with mummichogs in space followed as part of the Apollo–Soyuz Test Project and as part of a biological package aboard the Bion 3/Kosmos 782 satellite.NASA
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