Rainbow darters ( (Ray, et al., 2006)) 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.
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)
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)
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)
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)
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)
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)
Rainbow darters are not known to maintain a home range.
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)
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)
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)
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)
Rainbow darters may be sold as pets as an aquarium species, however, they do not have a major economic impact on humans. (Katula, 2005)
There are no known negative impacts of rainbow darters on humans.
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)
Kayla McNeilly (author), Radford University, Karen Powers (editor), Radford University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
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.
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.
an animal that mainly eats meat
uses smells or other chemicals to communicate
active at dawn and dusk
fertilization takes place outside the female's body
union of egg and spermatozoan
mainly lives in water that is not salty.
An animal that eats mainly insects or spiders.
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).
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
generally wanders from place to place, usually within a well-defined range.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the business of buying and selling animals for people to keep in their homes as pets.
chemicals released into air or water that are detected by and responded to by other animals of the same species
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
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