These fish have flattened heads and smiling mouths – the upward curve, like a dolphins, helps them feed on fish at the surface above them. Males are dark olive green with light yellow bellies and brilliant blue or orange vertical stripes along their sides, especially in the breeding season. Females are lighter and mostly yellow all over, though the color is lighter on their bellies. Females have no stripes. 

About hand-sized, mummichogs typically measure between 5 and 7 inches (12.7 and 17.8 centimeters) long. Females are usually larger than males. 

Native to coastal streams, estuaries and saltwater marshes, these little fish can live in both fresh and salt water – and even move back and forth between the two. They need areas with underwater vegetation. They can also tolerate staggering amounts of pollutants, meaning they do not live only in pristine waterways.  

Mummichog can be found along the Atlantic coast of North America, from the Gulf Coast of Texas all the way up to the Gulf of Saint Lawrence in Canada. 

They live up to 3 years in the wild.

Mummichogs may use their fins and body posture to communicate among themselves. 

Mummichogs prefer to eat at the water’s surface, where they eat tiny invertebrates, as well as fish eggs (even mummichog eggs!). They eat mosquitoes—up to 2,000 larvae a day—and can be used to help control mosquito populations. 

To survive cold weather, some mummichogs will bury themselves in underwater sediment – sometimes up to 8 inches (20 centimeters) deep! They will stay buried until the temperature reaches about 60 Fahrenheit (15 degrees Celsius).

True to the meaning of their name (“goes in crowds”) mummichog live in dense schools that can include hundreds of individual fish. 

Mummichogs can spawn up to eight times a year. The males’ colors grow more brilliant as breeding season—spring through summer—approaches. They use these bright colors to attract mates. Females display their silvery bellies as a way to signal readiness to spawn. Sometimes, the pair will swim together in tandem before mating.

Female mummichogs lay their eggs out of the water, on floating algae or on a rock or shell, where the male fertilizes them. She can lay up to 460 eggs at once. The eggs need air to develop for the first few weeks. After the next high tide, the water covers them which triggers hatching.

The larva stay in shallow water in the intertidal zone until they are 6 to 8 weeks old. When they are about 0.6 to 0.8 inches (15 to 20 millimeters) long, they swim to slightly deeper water and join schools with adults. They don’t reach their full growth until they are about 2 years old.

Mummichogs are not considered threatened. Local populations may be at risk from habitat loss and ecosystem degradation.