Mummichog

The name mummichog is derived from a Narragansett term meaning "going in crowds", which reflects the mummichog's strong shoaling tendency.^[7] 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.^[8]

Description

The body of the mummichog is elongate but thick, with a deep caudal peduncle. Usual length is 7.5 to 9 cm (3.0 to 3.5 in) but a maximum length of up to 15 cm (5.9 in) 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)^[9][10] 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.^{[citation needed]}

Adults of the two subspecies can be distinguished based on slight morphological^[11] and genomic^[12] 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.^[13][14]

The mummichog is very similar to the banded killifish, Fundulus diaphanus, and indeed the two species have been known to interbreed.^[15] 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.^{[citation needed]}

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, 175 km (109 mi) southeast of the closest point of mainland Nova Scotia in the Atlantic Ocean.^[16] The approximate geographical division between the two subspecies lies in New Jersey, Delaware and Virginia.^{[citation needed]}

Introduced populations have become established on the Atlantic coast of Portugal and southwestern Spain, starting in the 1970s^[17][18][19] and some have now reached the western Mediterranean basin.^[20] There may also be introduced populations in Hawaii and the Philippines.^[21] 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.^[22]

The mummichog is a common fish in coastal habitats such as salt marshes, muddy creeks, tidal channels, brackish estuaries, eelgrass or 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.^[23]

Diet

Mummichogs are agastric

They are also among fish species most tolerant of salinity changes (euryhaline).^[29] 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.^[30][31] They can even survive for a few hours in moist air outside of water, breathing air directly.^[32]

Populations have developed resistance to

Mummichogs live in dense shoals that can include several hundred individuals.^[citation needed]

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 20 cm (7.9 in) to overwinter.

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.[42]

The eggs are pale yellow, about 2 mm (0.08 in) 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.^[13] 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.^[13] Eggs therefore develop while exposed to moist air, and they hatch when the next high spring tides reach them.^[43][44][45] 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.^[46]

As opposed to their northern counterparts, the southern subspecies have eggs that lack filaments (adhesive chorionic fibrils)^[47] and they often deposit those eggs inside empty mussel shells.^[13][14] The two subspecies are also distinguished based on slight morphological^[11] and genomic^[12] differences.

Most mummichogs become sexually mature when two years old, around 3.8 cm (1.5 in) in length. Normal lifespan is four years.^[13]

Parasites

Mummichogs are hosts to a parasitic fluke, Homalometron pallidum, which has a complex lifecycle involving the aquatic snail, Ecrobia truncata.^[48] Other parasite species reported in mummichogs include 10 protozoans, eight trematodes, one nematode, two acanthocephalans, and two crustaceans.^[49] 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.^[50]

Interest to humans

Mummichogs readily eat mosquito larvae and attempts have been made to use them as biocontrol agents of mosquito populations.^[26]

Fishing

Mummichogs are sold as bait in sport fisheries for marine species such as summer flounder and bluefish, or even sometimes for freshwater species.^[26] 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.^[51]

Scientific utility

Mummichogs are considered an important environmental

• Japanese rice fish (Oryzias latipes), first fish to breed in space in 1994

References