Fundulus heteroclitus macrolepidotus
FAMILY
Fundulidae
TAXONOMY
Fundulus heteroclitus macrolepidotus Walbaum, 1792, northern America. In the 1980s, Able and Felley recognized the sub-species status of the northern populations of Fundulus heteroclitus.
OTHER COMMON NAMES
English: Killie, killifish; Spanish: Fúndulo; Portuguese: Fundulo.
PHYSICAL CHARACTERISTICS
Grows to 5 in (13 cm) in length. Sexually dimorphic and dichromatic. Males and females have up to 15 vertical bars, which tend to be faint or missing in mature adults. The mouth is blunt, with a turned-up lower jaw. The dorsal fin is positioned over the anal fin origin at about the midbody. Males have a dorsal ocellus. Breeding males are light gray to very black in background color. The body and all unpaired fins have bright iridescent white to greenish opalescent spots. The dorsal, anal, and caudal fins have a yellow margin that is less noticeable on the caudal fin in the black body variety. There is a yellowish cast to the abdomen and operculum, the latter with iridescent silver highlights. Color patterns and color intensities vary widely in both sexes. Females are larger than males. Body is chunky with a pale silvery background, brownish color on the back, and whitish color on the abdomen. The fins are clear. Adults rarely are confused with other species in their natural range.
DISTRIBUTION
From Chesapeake Bay, Maryland, United States, to Newfoundland, Canada. Naturalized in the estuary of the Guadalquivir River, southwestern Spain, and possibly established in the salt marshes of the estuary of the Guadiana River, at Castro Marim, southeastern Portugal.
HABITAT
The species is active primarily in tidally influenced coastal salt marshes as well as estuaries, tidal streams and creeks, shallow marine and brackish environments, and back-beach lagoons reached by high tides. They have been reported for freshwater portions of the Bronx River and naturalized in freshwater impoundments, the latter likely due to bait-bucket releases. Most studies of its habitat use have been undertaken in its primary habitat, the salt marshes.
BEHAVIOR
Traveling in huge schools numbering in the hundreds, the mummichog is in constant search of food. As a result, fishers find that they are caught easily in baited minnow traps. As a predator on salt marsh invertebrates and small fish, and as a prey item for wading birds and the blue crab, the northern mummichog has a significant impact on salt marsh trophic dynamics. The annual mortality rate is about 50% for adults and more than 99% for the larval and juvenile class sizes.
FEEDING ECOLOGY AND DIET
Feeds on a variety of marine and freshwater invertebrates, diatoms, mollusks, amphipods, crustaceans, plant material, insects, detritus, worms, and small fishes. It is doubtful that a mummichog would spurn anything edible that fits into its mouth. Mummichogs are preyed upon by larger fish and fish-eating birds.
REPRODUCTIVE BIOLOGY
Judging by its reproductive behavior in aquaria, the mummichog probably spawns continually in the spring and summer, but in nature its peak spawning activity is governed by a lunar cycle. Eggs are laid in clumps on floating algae mats or at the base of marsh grasses and buried in the sand in the high marshes at the very high tides of the new moon or full moon. The eggs are placed where desiccation will be minimized when the tide goes out. The eggs hatch when they are immersed again at the next very high tide. In aquaria water-incubated eggs hatch in about 16 days.
CONSERVATION STATUS
Not listed by the IUCN.
SIGNIFICANCE TO HUMANS
The mummichog is used as a bait fish and as an aquarium animal; it also is one of the most widely used laboratory animals. It is a harmless species unless it is swallowed live. It has been reported that many bored fishers have swallowed live mummichogs. In one such instance, some of the fish were infected with the larva of the nematode Eustrongyloides ignotus, causing stomach and intestinal problems for three fishers, two of whom required surgical intervention. Raasch noted, "Though 12 fishermen reported no symptoms from this pastime, the moral is that fishermen should abstain from taking the bait themselves when the fish refuse to do so."
