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 differences. and genomic 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. 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