Mummichog

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) but is generally olive-brown or olive-green. There can be vertical bars on the sides that are thin, wavy, and silvery.

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. The approximate geographical division between the two subspecies lies in New Jersey, Delaware and Virginia.

Mummichogs are agastric omnivores. Analyses of their gut contents have found diatoms, amphipods and other crustaceans, molluscs, fish eggs (including their own species), very small fish, insect larvae, and bits of eelgrass.

Mummichogs live in dense shoals that can include several hundred individuals.

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. They can also bury themselves in mud if they are caught in a drying tidal pool between spring tides. 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.

Spawning takes place from spring through fall. In the southernmost populations, up to eight spawnings are possible in a season. Spawning takes place most often at high tide and when the moon is new or full. Maximal spawning occurs when high spring tides coincide with night, though spawning during the day remains possible.

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.

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