The rainbow darter (''Etheostoma caeruleum'') is a small species of freshwater

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

, a darter from the

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

Etheostomatinae Etheosomatidae is a species rich subfamily of freshwater ray-finned fish, the members of which are commonly known as the darters. The subfamily is part of the family Percidae which also includes the perches, ruffes and pikeperches. The family i ...

, part of the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Percidae The Percidae are a family of ray-finned fish, part of the order Perciformes, which are found in fresh and brackish waters of the Northern Hemisphere. The majority are Nearctic, but there are also Palearctic species. The family contains more than ...

, which also contains the

perch Perch is a common name for fish of the genus ''Perca'', freshwater gamefish belonging to the family Percidae. The perch, of which three species occur in different geographical areas, lend their name to a large order of vertebrates: the Percif ...

es, ruffes and pikeperches. It is native to North America where it is found in small, fast-moving streams and small to medium-sized rivers. It grows to in length. The species is very sensitive to pollution and silt, staying in clean, pollution-free water. The rainbow darter is easily identified by three dark spots on the back, and blue and orange in the dorsal and anal fins.

Life

The rainbow darter lives in clean, rocky

riffles A riffle is a shallow landform in a flowing channel. Colloquially, it is a shallow place in a river where water flows quickly past rocks. However, in geology a riffle has specific characteristics. Topographic, sedimentary and hydraulic indica ...

from March through June. It has a lifespan of about 4 years. The males can grow up to 48 mm long, while the largest female reaches just under 43 mm. The male form is resplendent in bright oranges and iridescent blue spots, stripes, and checks.

Distribution

The rainbow darter is a small,

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

freshwater fish found in many creeks and small to medium-sized rivers throughout North America. In particular, it is common throughout the eastern United States, specifically throughout the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...

and

Ohio River Valley The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illinoi ...

regions. Its distribution extends south to northern parts of Alabama and as far west as Missouri and Arkansas.Kuehne, R., R. Barbour. 1983. ''The American Darters''. Lexington, Kentucky: The University Press of Kentucky. This distribution has been suggested to be due to once existing glaciers and to its intolerance of

brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estua ...

. One study to examine the phylogeography of ''E. caeruleum'' and its colonization patterns found its distribution is greatly due to historic glaciations, and furthermore, due to distributions from drainages which have since then resulted in the current morphological diversity of the rainbow darter.Ray, J. M, R.M. Wood, and A.M. Simons. 2006. Phylogeography and post-glacial colonization patterns of the rainbow darter, ''Etheostoma caeruluem'' (Teleostei: Percidae). ''Journal of Biogeography'' (33): 1550-1558. Geographically, the rainbow darter is one of the most abundant and common

Darter The darters, anhingas, or snakebirds are mainly tropical waterbirds in the family Anhingidae, which contains a single genus, ''Anhinga''. There are four living species, three of which are very common and widespread while the fourth is rarer and ...

species. Current distribution shown may be outdated and should be verified with state agencies. Particularly Texas where the species exists in limited number.

Ecology

The rainbow darter is classified as

insectivorous A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores were ...

, feeding on small invertebrates such as insects and crayfish, but it has also been known to feed on some fly larvae. In Four-Mile Creek in Ohio, the rainbow darter lives primarily on

trichoptera The caddisflies, or order Trichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the b ...

ns (i.e. caddisflies), having two feeding peaks: one in the morning and a second in the late afternoon or early evening.Adamson, S.W. and T.E. Wissing. 1977. Food habits and feeding periodicity of the Rainbow, Fantail, and Banded darters in Four-Mile Creek. ''Ohio Journal of Science'' (77): 164-169. The primary predators of the rainbow darter are larger freshwater fish, such as burbots (''

Lota lota The burbot (''Lota lota'') is the only gadiform (cod-like) freshwater fish. It is also known as bubbot, mariah, loche, cusk, freshwater cod, freshwater ling, freshwater cusk, the lawyer, coney-fish, lingcod, and eelpout. The species is closely ...

''), stonecats (''

Noturus flavus ''Noturus flavus'', the stonecat, is a North American freshwater catfish of the family Ictaluridae. The common name is due to its habit of hiding near or under stones in fast-moving water. Anatomy Stonecats are small, slender, flat-headed catfi ...

''), and smallmouth bass ('' Micropterus dolomieu''). Like many other darter species, it has the ability to maintain position on the substrate in flowing water.Carlson, R.L and G.V. Lauder. 2010. Living on the Bottom: Kinematics of Benthic Station-Holding in Darter Fishes (Percidae: Etheostomatinae). ''Journal of Morphology'' (271): 25-35. This unique characteristic plays a key role in its microhabitat preference. ''E. caeruleum'' has been shown to prefer creeks and rivers with rocky substrates and swift-moving riffles.Harding, J.M, A. J. Burky, and C.M. Way. 1998. Habitat Preferences of the Rainbow Darter, ''Etheostoma caeruleum'', with Regard to Microhabitat Velocity Shelters. ''Copeia'' (4): 988-997. This microhabitat preference has been suggested to be due to oxygen levels in the water during season changes or other factors, such as feeding or shelter-related habitat preferences. Because ''E. caeruleum'' has such a low tolerance for brackish water, human-induced changes such as pollution or sewer drainage has the potential to cause a significant negative impact on its abundance.

Life history

Darters have a wide range of life histories, but size correlates with most life history characteristics. For example, larger darters grow faster, live longer, produce bigger clutches, and have longer reproductive spans.Paine, M.D. 1990. Life history tactics of darters (Percidae: Etheostomatiini) and their relationship with body size, reproductive behavior, latitude and rarity. ''Journal of Fish Biology'' (37): 473-488. Mate selection by female darters is assumed to be common.Fuller, R.C. 2003. Disentangling female mate choice and male competition in the Rainbow Darter, ''Etheostoma caeruleum''. ''Copeia'' (1): 138-148. When examining the rainbow darter, life history traits were: average size 45 mm, growth 32 mm, maximum age four years, and clutch size 82. ''E. caeruleum'' mates during the spring, typically when water temperature is between 17 and 18 °C, and they will leave their normal microhabitat in the rapids to congregate on pebbles, where the stream leaves a pool, to mate. Once mates are selected, the fish mate repeatedly for several days until the female lays about 800 eggs. This darter also displays

group spawning A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

, and the males tend to exhibit

territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...

behavior during the breeding season.

Current management

Currently, the largest threat to ''E. caeruleum'' is run-off and pollution due to

urbanization Urbanization (or urbanisation) refers to the population shift from rural to urban areas, the corresponding decrease in the proportion of people living in rural areas, and the ways in which societies adapt to this change. It is predominantly t ...

. One study found the development of an interstate highway negatively affected the abundance of several fish species, including ''E. caeruleum'', because of decreasing quality of water of the nearby creek.Ritzi, C.M., B. L. Everson, J. B. Foster, J. J. Sheets, and D. W. Sparks. 2004. Urban ichthyology: changes in the fish community along an urban-rural creek in Indiana. ''Proceedings of the Indiana Academy of Science'' (113): 42-52. Currently, management plans consist of reducing nutrient, pesticide, and sediment loadings within such streams.Smiley, P.C., R. B. Gillespie, K. W. King, and C. Huang. 2009. Management implications of the relationships between water chemistry and fishes within channelized headwater streams in the Midwestern United States. ''Ecohydrology'' (2): 294-302. This same study suggests conservation practices should be a combination of both physical habitat monitoring and water chemistry monitoring, because it would benefit fish communities within headwater streams more than just implementing one conservation practice or the other. Although broad management plans are in place for many rivers and streams and their fish communities as a whole, no current management plans in place are specifically designed for ''E. caeruleum''.

References

* * * {{Taxonbar, from=Q217560 Etheostoma Taxa named by David Humphreys Storer Fish described in 1845