Mummichog

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 marshes. 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.

Taxonomy

The genus name ''Fundulus'' comes from ', 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 synonyms for this species include ''Cobitis heteroclita'', ''Fundulus fasciatus'', ''Fundulus pisculentus'', and ''Fundulus nigrofasciatus''.Scott, W.B., and Crossman, E.J. 1973. Freshwater fishes of Canada. Bulletin 184 of the Fisheries Research Board of Canada, Ottawa. 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 Lacépède created the genus in 1803.

The name mummichog is derived from a Narragansett term meaning "going in crowds", which reflects the mummichog's strong shoaling tendency. 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 cyprinid, eleotrid, and ptereleotrid 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.

Description

The body of the mummichog is elongate but thick, with a deep caudal peduncle. Usual length is but a maximum length of up to 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) 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 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.

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. 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 rakers, as opposed to 8–12 in the mummichog.

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, southeast of the closest point of mainland Nova Scotia in the Atlantic Ocean. The approximate geographical division between the two subspecies lies in New Jersey, Delaware and Virginia.

Introduced populations have become established on the Atlantic coast of Portugal and southwestern Spain, starting in the 1970s and some have now reached the western Mediterranean basin. There may also be introduced populations in Hawaii and the Philippines. 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.

The mummichog is a common fish in coastal habitats such as salt marshes, muddy creeks, tidal channels, brackish estuaries, eelgrass