By Tanya Dewey
Geographic Range
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. Populations in the Rocky Mountains of Wyoming and Colorado and the Ozark Mountains of Arkansas and Oklahoma are disjunct from other populations. They have been introduced to parts of Utah. (NatureServe, 2008)
Biogeographic Regions:
nearctic 
(introduced , native ).
Habitat
(209.92 ft)
Johnny darters are found in shallow water 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 are generally found in benthic parts of aquatic habitats, at depths of less than 0.5 m, although they have been captured in water as deep as 64 m. Johnny darters are considered pioneer species because they can quickly move in and become established in disturbed habitats. (Froese, 2008; NatureServe, 2008)
These animals are found in the following types of habitat:
temperate ; freshwater .
Aquatic Biomes:
benthic ; lakes and ponds; rivers and streams.
Physical Description
(3.03 in; avg. 2.01 in)
Johnny darters are small, slender fish with brown to yellow ctenoid scales, paler sides, and whitish bellies. 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. The first dorsal fin has 7 to 9 spines and the second dorsal find has 11 to 14 rays. Males become dusky to black on the head, upper body, and dorsal fins during the breeding season. The ventral portion of the pectoral fins and pelvic rays develop whitish, knobby tips. The average length is 51 mm and the largest recorded individual was 77 mm. (Becker, 1983)
Some key physical features:
ectothermic ; heterothermic ; bilateral symmetry .
Sexual dimorphism: sexes colored or patterned differently.
Development
Johnny darters spawn in waters from 11.7 to 21.1 degrees Celsius. Temperature influences length of development to hatching, with eggs laid in April (12.8 degrees Celsius) hatching at 16 days and eggs laid in May (20 degrees Celsius) hatching at 10 days. Larvae are 5 mm long at hatching and generally grow to 29 to 54 mm by September. (Becker, 1983)
Reproduction
Johnny darters breed once yearly.
Spawning occurs in the spring, usually in April or May.
Johnny darter males migrate to spawning areas before females and establish small nesting territories in protected, shallow waters. Males select a stationary object of at least 25 cm in diameter, such as a log, rock, or even trash under which spawning occurs. Males compete for nesting territories, with a side-by-side display that helps them to establish dominance. Once one is established as dominant, it drives the other male away. Male Johnny darters aggressively defend their nests, even against fish up to 3 times their size. They attack by butting the threat with their head and biting at the fins of an intruding fish. Johnny darters clean the underside of the chosen spawning object with their anal, pectoral, and tail fins. They also enlarge the nest with movements of their body. Males rarely leave their territory during the day, but territories are not defended at night. Males first swim aggressively towards females that approach their nest, but then begin to swim upside down under their 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 move along the object and deposit eggs. Females place one egg at a time on the object, eventually creating a small, single layer patch of eggs up to 13 cm in diameter. Females mate with 4 to 6 males and males typically mate with more than 1 female. (Becker, 1983)
Mating systems:
polygynandrous (promiscuous) .
Females lay from 30 to 200 eggs at each spawning event, which they will do several times in the nests of different males. Male nests have been recorded with between 30 and 1150 eggs in them. Smaller females have been recorded with from 48 to 299 eggs and larger females with from 86 to 691 eggs. Johnny darters can breed in their first year after hatching. (Becker, 1983)
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (external ); oviparous .
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)
Parental investment:
pre-fertilization (provisioning, protecting: female); pre-hatching/birth (protecting: male).
Lifespan/Longevity
Johnny darters live for up to 3 years. (Becker, 1983; Froese, 2008)
Behavior
Johnny darters are solitary fish that live in bottom habitats in freshwater streams and lakeshores. They are active during the day. (Becker, 1983)
Home Range
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)
Key behaviors:
natatorial ; diurnal ; motile ; sedentary ; solitary ; territorial .
Communication and Perception
Johnny darters use their large eyes and keen vision to find prey. They don't respond strongly to olfactory cues. Tactile and visual signals are used in mating communication. They have a complete lateral line. (Becker, 1983)
Perception channels:
visual ; tactile ; vibrations ; chemical .
Food Habits
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, such as Hyalella, Cyclops, and Daphnia. (Froese, 2008)
Primary Diet:
carnivore (insectivore , eats non-insect arthropods).
Animal Foods:
insects; aquatic crustaceans.
Predation
- lake trout (Salvelinus namaycush)
- lake whitefish (Coregonus clupeaformis)
- burbot (Lota lota)
- smallmouth bass (Micropterus dolomieu)
- yellow perch (Perca flavescens)
- herons (Ardeidae)
- water snakes (Nerodia)
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)
Anti-predator adaptations::
cryptic .
Ecosystem Roles
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)
Economic Importance for Humans: Negative
There are no negative effects of Johnny darters on humans.
Economic Importance for Humans: Positive
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)
Conservation Status
IUCN Red List: [link]:
Not Evaluated.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
State of Michigan List: [link]:
No special status.
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)
For More Information
Find Etheostoma nigrum information at
Contributors
Tanya Dewey (author), Animal Diversity Web, University of Michigan Museum of Zoology.
