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Etheostoma caeruleumRainbow darter

By Kayla McNeilly

Geographic Range

Rainbow darters (Etheostoma caeruleum) are native to the Nearctic region. Year-round, this species inhabits small rivers and streams in eastern North America. Rainbow darters have been widely located in vast numbers in the Ohio River valley and the tributaries of the Great Lakes. They are also found throughout the Mississippi River, as far north as Minnesota and as far south as southeastern Louisiana. This species also is located in the Potomac River in Maryland and Virginia, the Little Miami River in Ohio, the Hudson Bay tributaries in Minnesota, the Missouri River in Missouri, the Kanawha River in West Virginia and Virginia, the Wabash River in Indiana, the Green river in Tennessee and Kentucky, and the Osage River in Missouri. (Ray, et al., 2006)

Habitat

Rainbow darters are commonly found in cool running freshwater streams and small rivers. They are most common in gravel, rocky, or sandy substrates in fast-moving shallow riffles and can withstand freezing temperatures of an average of 15 degrees Celsius. They avoid heavily polluted and silty waters. When nesting or feeding, these darters are more frequent in deeper, slow-moving pools. They are typically located around small confined areas in shallow, clear waters. Rainbow darters are most common under or along the side of larger rocks and debris in small rapids. They are typically found at depths of 0.1 to 0.5 m. (Gilbert and Williams, 2002; Harding, et al., 1998; Page and Burr, 1991; Schlosser and Toth, 1984; Trautman, 1981; Wynes and Wissing, 1982)

  • Aquatic Biomes
  • rivers and streams
  • Range depth
    0.1 to 0.5 m
    0.33 to 1.64 ft

Physical Description

As adults, rainbow darters can reach lengths of about 6 to 8 cm. Both males and females have a frenulum, a little, folded portion of tissue that restricts movement in the mouth. They also have a straight tail, two anal spines, and two dorsal fins with 10 to 11 layered spines. Breeding males are a brilliant combination of bright colors and stripes meant to stand out. Specifically, they have brownish-olive green base saddles that lay vertically along the body. On the dorsal side, they have 8 to 13 dark blue-greenish bands that wrap around the body. Towards the middle of the body, the color between the saddles shifts to reddish-orange that continues to the tail fin. The underside has an orange-yellow edge, transitioning to a blue-green belly. The first dorsal fin has a sliver of a reddish-orange, a horizontal layer that blends into a dark blue top. The second dorsal fin has a reddish-orange bottom layer, but covers most of the fin until it blends horizontally with a sliver of dark blue at the tip. The first anal fin is bluish green, while the second anal fin has a dark blue-green tip, with reddish-orange in the middle. In the non-breeding season, male patterns are less showy. Oftentimes, they are described as clearer and more transparent. Adult females also have duller, more brownish-olive green colors. They have similar saddle bands as males, but they are less obvious, more spread out, and have no dark blue bands. Females have a bluish tint along their body. The two dorsal fins are almost transparent with dark brown spotted rows horizontally. The two anal fins are similar, with fewer brown horizontal spots. Juveniles are more similar to females in their early stages, gaining vibrant colors as they age. (Kuehne and Barbour, 1983; Trautman, 1981)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • Range length
    5 to 8 cm
    1.97 to 3.15 in
  • Average length
    6.2 cm
    2.44 in

Development

Adult rainbow darters spawn between March and June. The eggs are clear or transparent with a yellow tent yolk and a small black drop in the middle of the yolk. The length of the eggs averages 1.7 to 2 mm. The larvae hatch after 10 to 12 days, in water temperatures of 17 to 19 degrees Celsius. During the days before hatching, larvae develop a heartbeat on day 2 and their skeleton and teeth are apparent at day 8. Chromosomes determine the sex of rainbow darters. Hatching larvae are 6.0 to 6.2 mm long. From larva to juvenile, the process takes about 18 to 21 days, with juveniles reaching lengths of about 13.0 to 15.0 mm. Juveniles are known to eat aquatic water insects and small freshwater shrimp. Juveniles reach adulthood about 47 days after hatching. (Cooper, 1979; Paine and Balon, 1984)

Reproduction

During the reproductive season, both male and female colors become brighter. When females are ready for spawning, they travel to pools where the males live. Females are known to spawn multiple times over the reproductive season. Males that are larger or more colorful have a higher chance of reproducing. They use their size and color advantages to scare off lesser males. Multiple males will follow one female until she picks one, usually the brighter and bigger male. Once the female picks the male, she then buries her fins and torso into the gravel or sand of the streambed, only her head and tail stay unburied as she faces upstream. She buries and unburies herself several times, until she signals to the male. The male proceeds behind the female and mounts. They begin the spawning process with the two fish “vibrating” as a pair. The female releases her eggs, while the male releases his sperm, fertilizing the eggs. The male only has approximately 20 seconds to fertilize the eggs. The pair will repeat this process several times as they move upstream, a short distance at a time. They proceed until other males disturb them, which is very common. (Fuller, 1999; Reeves, 1907)

Rainbow darters’ reproduction is dependent upon water temperature and region. They spawn in temperatures between 15 to 18 degrees Celsius, which across their range includes the months of March through June. At a particular locale, the breeding season is limited to around three months. After their eggs are fertilized, they are sticky and become buried in the sand or gravel stream bottom. The eggs are about 1.5 mm, with a mass of around 0.0001 grams. They have a spherical shape, with a pale yellowish-color and appear to have a large black drop in the middle. It takes several days, but a female can lay up to 800 eggs. Each clutch includes around 14 to 60 eggs. Researchers suggest juveniles reach adulthood 47 days after hatching and wait until the next spawning season to reproduce. (Heins, et al., 1996; Reeves, 1907)

  • Breeding interval
    Rainbow darters spawn yearly.
  • Breeding season
    These fish spawn between the months of March and June in temperatures of 15 to 18 degrees Celsius.
  • Range number of offspring
    800 (high)
  • Range time to hatching
    10 to 12 days
  • Average time to independence
    0 days

Rainbow darters are not nesting fish. Their eggs become buried along the streambed wherever they spawned. These fish offer no parental guidance. (Heins, et al., 1996; Reeves, 1907)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

The average lifespan of wild rainbow darters is three years. Their maximum recorded wild lifespan is five years. Their captive lifespan has not been reported. (Beckman, 2002; Gilbert and Williams, 2002; Page and Burr, 1991)

  • Range lifespan
    Status: wild
    5 (high) years
  • Average lifespan
    Status: wild
    3 years
  • Average lifespan
    Status: wild
    3 years
  • Average lifespan
    Status: captivity
    3 years
    AnAge

Behavior

Rainbow darters are considered “shy” and stay hidden for most the day between or along rocks unless they are actively foraging or reproducing. During their breeding season, they are more social; at this time, males follow females in hopes of reproducing. Males communicate with their vibrant colors and size. If rainbow darters are threatened, they will hide and not move until the danger has passed. Darters are alerted of danger through pheromones emitted when another darter is injured and skin is torn. If they feel threatened by another species close to their own, males have been known to try and scare them away by flapping their gills. Rainbow darters are crepuscular, active during dusk and dawn. They are active swimmers and do not defend territories except when breeding or finding food. (Commens and Mathis, 1999; Crane, et al., 2009; Reeves, 1907)

Home Range

Rainbow darters are not known to maintain a home range.

Communication and Perception

Rainbow darters have the ability to detect chemical cues and behaviors from one another. In a situation where a rainbow darter is being attacked by a predator, it can release a chemical pheromone cue that alerts other rainbow darters to the danger once the skin has been torn. Other darters respond to this cue by decreasing activity, in an effort to be less detectable by predators. Rainbow darters respond aggressively to similar species, such as bumblebee gobies and yoke darters, by flapping their gills. They are seen as competitors and a threat to their food supplies and young. Males and females also use their vibrant colors for communication. During the breeding season, these bright colors attract possible mates. (Commens and Mathis, 1999; Crane, et al., 2009; Gibson and Mathis, 2006)

Food Habits

Rainbow darters are insectivores that consume many types of small invertebrates. A diet study showed a strong preference for caddisflies, which include the genera Hydropsyche and Cheumatopsyche. Other, smaller components include a variety of flies, including midges and black flies. They also eat mayflies from the genus Baetis. Uncommon parts of their diet include other caddisfly genera (Chimarra), aquatic larvae, small snails, nematodes, small crayfish, and a variety of fish eggs such as minnow and lamprey eggs. Rainbow darters often eat twice a day: early in the morning and late in the afternoon or evening. Their diets change seasonally due to changes in water temperatures and availability of invertebrates. In preparation for the decreased food supply in the winter, rainbow darters eat more between mid-August until mid-October. In April and May, their feeding habits increase and drop during the high temperatures of the summer. (Adamson and Wissing, 1977; Kuehne and Barbour, 1983; Wynes and Wissing, 1982)

  • Animal Foods
  • eggs
  • insects
  • mollusks
  • terrestrial worms
  • aquatic crustaceans

Predation

Rainbow darters have many predators in their habitats. They are fed upon by many larger fresh water fish including smallmouth bass, spotted bass, bluegills, longear sunfish, creek chubs, and crayfish. If rainbow darters are threatened, they will hide and not move until the danger is gone. These darters can also give off a chemical signal to other darters alerting them to the danger. Once a victim’s skin or tissue has been torn, the chemical is released, warning other rainbow darters of the danger. (Harding, et al., 1998; Kuehne and Barbour, 1983)

Ecosystem Roles

Researchers have found two different kinds of parasites acanthocephalans known as thorny-headed worms, Acanthocephalus dirus and Pomphorhynchus bulbocolli. These parasites damage the tissues and muscle layers on the rainbow darters. Additional parasites are two freshwater mussels Ptychobranchus occidentalis and Venustaconcha pleasii. These parasites enter through the gills, attaching to the inside of the darters for days at a time, until they reach the juvenile stage. Researchers have found darter behavior may change with infections of these parasites, which could become fatal for the fish. It has been reported that the parasite reduces activity in rainbow darters and they lose body mass. They also show a weaker response to chemical alarm cues given in the presence of predators. More than half of the rainbow darters that were collected in the James River in Greene County, Missouri have these parasites. (Crane, et al., 2011; Kuehne and Barbour, 1983; McDonough and Gleason, 1981)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Rainbow darters may be sold as pets as an aquarium species, however, they do not have a major economic impact on humans. (Katula, 2005)

Economic Importance for Humans: Negative

There are no known negative impacts of rainbow darters on humans.

Conservation Status

The IUCN Red List considers rainbow darters to be a species of “least concern.” Its population is listed as stable and no management action is required at this time. In fact, they are one of the most abundant darter species in their range. (Kuehne and Barbour, 1983; NatureServe, 2013)

Contributors

Kayla McNeilly (author), Radford University, Karen Powers (editor), Radford University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Adamson, S., T. Wissing. 1977. Food habits and feeding periodicity of the rainbow, fantail, and banded darters in Four Mile Creek. Ohio Journal of Science, 77/4: 164-169.

Beckman, D. 2002. Comparison of aging methods and validation of otolith ages for the rainbow darter, Etheostoma caeruleum. Copeia, 2002/3: 830-835.

Commens, A., A. Mathis. 1999. Alarm pheromones of rainbow darters: Responses to skin extracts of the conspecifics and congeners. Journal of Fish Biology, 55/6: 1359-1362.

Cooper, J. 1979. Description of eggs and larvae of fin tail (Etheostoma flabellare) and rainbow (E. caeruleum) darters from Lake Erie tributaries. Transactions of the American Fisheries Society, 108/1: 46-56.

Crane, A., D. Woods, A. Mathis. 2009. Behavioural responses to alarm cues by free-ranging rainbow darters (Etheostoma caeruleum). Behaviour, 146/11: 1565-1572.

Crane, A., A. Fritts, A. Mathis, J. Lisek, C. Barnhart. 2011. Do gill parasites influence the foraging and antipredator behaviour of rainbow darters, Etheostoma caeruleum?. Animal Behaviour, 82/4: 817-823.

Fuller, R. 1999. Cost of group spawning to guarding males in the rainbow darter, Etheostoma caeruleum. Copeia, 1999/4: 1084-1088.

Gibson, A., A. Mathis. 2006. Opercular beat rate for rainbow darters Etheostoma caeruleum exposed to chemical stimuli from conspecific and heterospecific fishes. Journal of Fish Biology, 69/1: 224-232.

Gilbert, C., J. Williams. 2002. National Audubon Society Field Guide to Fishes (North American). New York: Alfred A. Knopf.

Harding, J., A. Burky, C. Way. 1998. Habitat preferences of the rainbow darter, Etheostoma cearuleum, with regard to microhabitat velocity shelters. Copeia, 1998/4: 988-997.

Heins, D., J. Baker, D. Tylicki. 1996. Reproductive season, clutch size, and egg size of the rainbow darter, Etheostoma caeruleum, from the Homochitto River, Mississippi, with evaluation of data from the literature. Copia, 1996/4: 1005-1010.

Katula, R. 2005. "Darters: Aquarium Care and Design Guidelines" (On-line). Accessed July 31, 2014 at http://www.nanfa.org/articles/acdarteraquariums.shtml.

Kuehne, R., R. Barbour. 1983. The American Darters. Lexington, Kentucky: The University Press of Kentucky.

McDonough, M., L. Gleason. 1981. Histopathology in the rainbow darter, Etheostoma caeruleum, resulting from infections with the acanthocephalans, Pomphorhynchus bulbocolli and Acanthocephalus dirus. The Journal of Parasitology, 67/3: 403-409.

NatureServe, 2013. "Rainbow darter" (On-line). IUCN Red List of Threatened Species. Version 2013.2. Accessed March 31, 2014 at http://www.iucnredlist.org/details/202458/0.

Page, L. 1983. Handbook of Darters. Neptune City, NJ: TFH Publications.

Page, L., B. Burr. 1991. A Field Guide to Freshwater Fishes of North America North of Mexico. Boston: Houghton Mifflin Company.

Paine, M., E. Balon. 1984. Early development of the rainbow darter, Etheostoma caeruleum, according to the theory of saltatory ontogeny. Environment Biology of Fishes, 11/4: 277-299.

Paulson, N., J. Hatch. 2002. "Rainbow Darters" (On-line). Minnesota Pollution Control Agency. Accessed November 12, 2002 at http://www.pca.state.mn.us/kids/fish/rainbowdarter.html.

Ray, J., N. Lang, R. Wood, R. Mayden. 2008. History repeated: Recent and historical mitochondrial introgression between the current darter Etheostoma uniporum and rainbow darter Etheostoma caeruleum (Teleostei: Percidae). Journal of Fish Biology, 72/2: 418-434.

Ray, J., R. Wood, A. Simons. 2006. Phylogeography and post-glacial colonization patterns of the rainbow darter, Etheostoma caerueum (Teleostei: Percidae). Journal of Biogeography, 2006/33: 1550-1558.

Reeves, C. 1907. The breeding habits of the rainbow darter (Etheostoma coeruleum Storer), a study in sexual selection. Marine Biological Laboratory, 14/1: 35-59.

Schlosser, I., L. Toth. 1984. Niche relationships and population ecology of rainbow (Etheostoma caeruleum) and fantail (E. flabellare) darters in a temporally variable environment. Oikos, 42/2: 229-238.

Trautman, M. 1981. The Fishes of Ohio. Athens, Ohio: Ohio State University Press, Ohio Grant Program Center for Lake Erie Area Research.

Weston, M., R. Johnson. 2008. Visible impact elastomer as a tool for marking Etheostomine darters (Actinopterygii: Percide). Southeastern Naturalist, 7/1: 159-164.

Williams, J., C. Gilbert. 2002. National Audubon Society: Field Guide to Fishes (North America). New York, NY: Alfred A. Knopf.

Wynes, D., T. Wissing. 1982. Resource sharing among darters in an Ohio stream. American Midland Naturalist, 107/2: 294-304.

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