Johnny darters are small, slender fish with brown to yellow scales, paler sides, and whitish bellies. They average 51 mm in length. The backs and sides are marked with darker "saddle marks" and the sides have distinctive "W" shaped brown spots along the lateral line. There is a dark stripe that extends from the mouth to the eye, the dorsal fins are marked with brown spots, the tail fin has brown stripes, and the pectoral and anal fins are clear. Males become black on the head, upper body, and dorsal fins during the breeding season and they develop whitish knobby tips on their lower fins.
Johnny darters are found throughout eastern North America, from Wyoming, Colorado, the Dakotas, and Saskatchewan east to the Atlantic seaboard as far south as North Carolina. They are also found south into Alabama and Mississippi.
Johnny darters are found in shallow water (usually less than 0.5 m) in small to medium sized rivers, creeks, streams, and headwaters. They are found in areas with sandy, muddy, or rocky substrates, but are more common over sandy or gravel substrates in slow-moving water. They are also found along the sandy shores of lakes or large rivers.
Johnny darters spawn in waters from 11.7 to 21.1 degrees Celsius, taking from 10 to 16 days to hatch. Larvae are 5 mm long at hatching and generally grow to 29 to 54 mm by September.
Johnny darter males migrate to spawning areas before females and establish small nesting territories in protected, shallow waters. Males choose a stationary object, such as a log, rock, or even trash, that they will use as a nest. Males compete for nesting territories and aggressively defend their nests, even against fish up to 3 times their size. Johnny darters clean the underside of their chosen spawning object with their fins. They also enlarge the nest with movements of their body. When a female approaches, a male will begin to swim upside down under the spawning object, which attracts the female. The female swims upside down under the spawning object, alongside the male, who then prods her sides. This stimulates the female to deposit eggs, one at a time on the object, creating a small, single layer patch of eggs. Females deposit eggs in the nests of different males, and most males have several females deposit eggs in their nest.
Females can have from 86 to 691 eggs, which they lay in small batches in the nests of different males. Male nests have been recorded with between 30 and 1150 eggs in them. Johnny darters can breed in their first year after hatching.
Johnny darter eggs are attached to the underside of rocks and guarded by males until they hatch. Males rub the eggs with their fins to clean them from 13 to 16 times an hour. They also fan the eggs with their pectoral fins. When an eggs becomes covered with fungus, the male will eat it. Males aggressively defend their eggs against fish that might want to eat them. (Becker, 1983; Froese, 2008)
Johnny darters are solitary fish that live in bottom habitats in freshwater streams and lakeshores. They are active during the day. (Becker, 1983)
Males defend breeding territories during the breeding season and may make small migrations to breeding areas. Otherwise, there is little information on home ranges or their size. (Becker, 1983)
Johnny darters use their large eyes and keen vision to find prey. They don't seem to have a good sense of small. They use touch and vision in communication during mating.
Johnny darters feed on small insect larvae and crustaceans as both adults and young. Young feed on much smaller prey, such as tiny midge larvae and ostracods. Adults eat midge larvae, mayfly nymphs, caddisfly larvae, blackfly larvae, and small crustaceans.
Johnny darters are eaten by larger, predatory fish, including lake trout, lake whitefish, burbot, smallmouth bass, yellow perch, and others. Because of their shallow water habits, they are also likely prey of wading and diving birds, such as herons, and water snakes. Johnny darters are cryptically colored. (Becker, 1983)
Johnny darters are important members of native aquatic ecosystems, they are important predators of small invertebrates and are prey for larger predatory fish, including game fish, and wading and diving birds. (Becker, 1983)
There are no negative effects of Johnny darters on humans.
Johnny darters are important members of native aquatic ecosystems and are some of the first fish to colonize disturbed aquatic habitats. They are important prey for larger game fish. (Becker, 1983)
Johnny darters are not considered threatened throughout most of their range. They are considered vulnerable or imperiled in some states, including Arkansas, Kentucky, Oklahoma, Kansas, and Nebraska. Johnny darters are tolerant of high levels of silt and some pollution and are able to colonize disturbed aquatic habitats readily. (Becker, 1983; NatureServe, 2008)
Tanya Dewey (author), University of Michigan-Ann Arbor.
Becker, G. 1983. Fishes of Wisconsin. Madison, Wisconsin: The University of Wisconsin Press.
Froese, R. 2008. "Etheostoma nigrum" (On-line). fishbase.org. Accessed December 11, 2008 at http://www.fishbase.org/Summary/SpeciesSummary.php?id=3445.
NatureServe, 2008. "Etheostoma nigrum" (On-line). NatureServe Explorer: An online encyclopedia of life. Accessed December 12, 2008 at http://www.natureserve.org/explorer/servlet/NatureServe?searchName=Etheostoma%20nigrum.