About Fundulus heteroclitus (Linnaeus, 1766)
Fundulus heteroclitus, commonly called the mummichog, has an elongated but thick body with a deep caudal peduncle. It typically reaches 7.5 to 9 cm (3.0 to 3.5 in) in length, with a maximum recorded length of 15 cm (5.9 in). Its mouth is upturned, and the lower jaw protrudes when the mouth is closed; both the 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. While the body has no lateral line, lateral line pores are present on the head. Coloration is variable, and individual mummichogs can even change shade when placed near different backgrounds; overall color is generally olive-brown or olive-green. Thin, wavy, silvery vertical bars may be present on the sides. During the reproductive season, males display more intense coloration: they become dark olive-green on the back, steel-blue on the sides with around 15 silvery bars, and yellow or orange-yellow on the underside. The male dorsal fin is mottled, and a small eyespot may be present near its rear edge. Females are typically paler, lack bars and intense belly yellowing, and have uniformly colored dorsal fins. The species is split into two subspecies, which can be distinguished by slight morphological and genomic differences. Northern subspecies eggs have adhesive chorionic fibrils (filaments) that southern subspecies eggs lack; the northern subspecies deposits eggs in sand, while the southern subspecies often lays eggs inside empty mussel shells. The mummichog is very similar to the banded killifish, Fundulus diaphanus, and the two species are known to interbreed. Their habitats may overlap, but banded killifish are more commonly found in freshwater, which is not typical for mummichog. Banded killifish have thin dark bars on a light-colored side, while mummichog have thin light bars on a dark-colored side. Internally, banded killifish have 4–7 gill rakers, while mummichog have 8–12 gill rakers. This species is native to the Atlantic coast of North America, ranging from the Gaspé Peninsula, Anticosti Island, and Port au Port Bay in the north to northeastern Florida in the south. It is also found on Sable Island, 175 km (109 mi) southeast of the nearest point of mainland Nova Scotia in the Atlantic Ocean. The approximate geographic boundary between the two subspecies runs through New Jersey, Delaware, and Virginia. Introduced populations have become established on the Atlantic coast of Portugal and southwestern Spain beginning in the 1970s, and some have now spread to the western Mediterranean basin. Possible introduced populations also exist in Hawaii and the Philippines. As bait fish, mummichogs are sometimes released into freshwater habitats where they can survive; there are documented records of individuals in New Hampshire ponds, the upper Ohio River, and the Beaver River. Mummichogs are common in coastal habitats including salt marshes, muddy creeks, tidal channels, brackish estuaries, eelgrass and cordgrass beds, and sheltered shorelines. They occur in coastal rivers but rarely venture beyond the head of tide. A small number of landlocked populations exist in freshwater lakes close to shore, for example on Digby Neck, Nova Scotia. Spawning occurs from spring through fall. In the southernmost populations, up to eight spawning events can occur in a single season. Spawning most often takes place at high tide, during new or full moons. Maximum spawning occurs when high spring tides coincide with night, though spawning can also happen during the day. During courtship, males may pursue females, and females may attract males by turning onto their sides near the bottom and flicking their tails. After a male and female swim together for some time, the male crowds the female against a rock or plant and clasps her, curving his larger dorsal and anal fins around her body. Finger-like projections that develop on the male's scales behind and below the dorsal fin may help him maintain contact with the female. The pair quivers vigorously to release eggs and sperm. The eggs are pale yellow, around 2 mm (0.08 in) in diameter, and strongly adhesive. During a single spawning event, a female can deposit up to 740 eggs in separate clutches of 10 to 300 eggs each. The eggs adhere to plants, algal mats, empty mussel shells, sand, or mud at sites that are only covered by water during high spring tides. Eggs develop while exposed to moist air, and hatch when the next high spring tides reach them. Eggs cannot hatch in air or moving water; hatching is triggered by low oxygen, which occurs in the boundary layer of relatively still water surrounding the metabolically active egg at high tide, but not in air or moving water. Most mummichogs reach sexual maturity at two years old, when they are around 3.8 cm (1.5 in) in length. The typical lifespan of a mummichog is four years.
