Fathead Minnow

The fathead minnow in its wild form is generally dull olive-grey in appearance, with a dusky stripe extending along the back and side, and a lighter belly. There is a dusky blotch midway on the dorsal fin. Breeding males acquire a large, grey fleshy growth on the nape, as well as approximately 16 white breeding tubercles on the snout.

Typical total lengths are between 7 and 10 cm (2.8 and 3.9 in).

Fathead minnows are distributed across North America from Chihuahua, Mexico, north to the Maritime Provinces and Great Slave Lake drainage of Canada and have been introduced to Atlantic and Pacific coastal drainage basins in the United States. Their tolerance for multiple environmental conditions, characteristics of their life history, and their popularity as bait species contribute to their widespread distribution. The fathead minnow is quite tolerant of turbid, low-oxygen water and can most commonly be found in small lakes, ponds, and wetlands. They can also be found in larger lakes, streams, and other habitats.

Fathead minnows are omnivores that are categorized as Benthic filter feeders, sifting through dirt and silt to find food. The carnivorous portion of their diet is made up of mainly insects, crustaceans, other aquatic invertebrates, and zooplankton. The herbivorous portion of their diet is primarily made up of algae and phytoplankton. Fathead minnows will also feed on bottom detritus.

Fathead minnows are a largely preyed upon fish that is eaten by mainly piscivorous fish such as Largemouth Bass, Northern Pike, Yellow Perch, Walleye, and various other types of fish.

In the fathead minnow, the female supplies the eggs and the male cares for them until they hatch. The male defends a nest as females pass by and spawn eggs to be cared for by the male. In choosing a nest site, the newly reproductive male fathead minnow tends to take over the nest site of a parental male and evicting its resident rather than occupying an empty one. Also, when given the choice between different unguarded nest sites, it will usually choose the one that already contains eggs. The newer and more numerous the eggs are in the nest site, the more likely the current male is to be challenged by the newcomer. The new male will care for the old male's eggs, a behavior called allopaternal care.

The fathead has been very commonly used as a baitfish, and more recently has emerged in the aquarium trade as the rosy-red minnow. This colour morph was discovered in several Arkansas breeding farms in 1985. Both sexes of this strain have a rosy-golden body and fins and may express dark splotches of wild-type fathead coloration, and are sold in pet shops primarily as feeder fish. They can also be used in home aquariums as pets.

The fathead's invasive status in Europe is cited as the main cause for the spread of enteric redmouth disease among trout and eels there. Established feral populations have been found in France (in 1991), Flanders in Belgium (1995), the Netherlands (2008) and Germany (2015). A small UK population, first discovered in 2008, was declared eradicated the same year.