Iowa darter (Etheostoma exile)
|Size||Average female length: 6.5 cm (2)|
Average female weight: around 2 g (2)
- The Iowa darter is found farther west than any other darter species in North America.
- The male Iowa darter becomes extremely colourful during the breeding season.
- The Iowa darter is one of Montana’s smallest fish.
- The Iowa darter migrates to shallow water to reproduce.
The Iowa darter is classified as Least Concern (LC) on the IUCN Red List (1).
The specific part of the scientific name of the Iowa darter (Etheostoma exile) means ‘slim’ in Latin (2), and refers to the slender body of this fish species (3). The colouration of the male Iowa darter changes dramatically during the breeding season, although when it is not breeding its appearance is similar to that of the female. The upperside of this species is mostly brown and the sides of the body are mottled with between 9 and 12 large dark bars. The underside of the Iowa darter is white, light olive-green or tan (4). There is a dark, tear-shaped mark underneath each eye of both sexes (3).
As with other Percidae species, the dorsal fin is split into two (3), of which the anterior fin has a dark lower half with a light upper half and dark edges. The posterior dorsal fin and caudal fin are both patterned with spots. The other fins are either colourless or have a very slight pigmentation (4). The snout of this species is rounded (5) and the caudal fin is squarish (3) (4). The impressively sized pectoral fins of this species are fan-shaped (3).
During the breeding season, the male Iowa darter becomes much more brightly coloured, with the blotches along the side of the body turning blue-green and a pattern of bright red spots appearing in this area. The colouration of the fins becomes much more vivid, especially the anterior dorsal fin which becomes bright blue-green and is also patterned with bright red spots (3). The underside of the male becomes bright orange-red during the breeding season (5).
The female Iowa darter is slightly larger than the male (2) and does not change its appearance during the breeding season, retaining its mottled brown colouration. The female has the same colouration on its dorsal fin as the male, although the fin is slightly duller and is also smaller (5).
The range of the Iowa darter stretches south from southern Quebec and northern Alberta in Canada to Ohio, Illinois and Colorado in the United States. This fish is found farther west than any other darter species (1).
The Iowa darter generally inhabits still or slow-moving water bodies, such as small rivers, streams (1) (2) (5), ponds and lakes (1) (2) where there is abundant vegetation (1) (2) (5). This fish is most common in slightly acidic water with a pH of 6, although it does not occur in any water with a lower pH than this (5).
The Iowa darter migrates from deep to shallow water to reproduce, with the male usually migrating before the female. The breeding season varies depending on the location of the population, with those in Wisconsin spawning between late April and mid-June and those in Illinois and Michigan spawning from April to May in (5). When the male arrives in the shallow area, it establishes a territory which it protects from other males (2) (3). When a female enters the territory, the male swims around it in circles until the female eventually positions itself over a suitable spawning area (2) (3) (5). The female then vibrates her body to release the eggs onto the substrate while the male, which positions itself behind the female, fertilises them (2) (3). The average clutch of the Iowa darter contains around 250 eggs which develop for between 12 and 26 days before hatching (2).
The diet of the Iowa darter is composed mostly of invertebrates such as copepods, water fleas and midge larvae (2) (3) (5). This fast-moving fish lacks a swim bladder (3) (5) and makes short, rapid movements to capture its prey (3). This relatively long-living fish species can live for up to two or three years (2).
The Iowa darter has experienced a population decline in many areas throughout its range (1) (5), including Ohio and Illinois where the population is thought to have decreased due to agricultural pollution and other habitat modifications that have been caused by humans (5). This fish species is intolerant of pollutants, especially those that decrease the amount of aquatic plants within its habitat which are vital to its survival (5). The introduction of invasive species may also have reduced certain populations (1).
There are not currently known to be any conservation measures in place for the Iowa darter and it is not thought to need any research or monitoring (1), although people who collect or keep this fish species are required to apply for a permit (2).
The Iowa darter is classified as endangered in Illinois (5).
Find out more about the Iowa darter:
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- Anterior: situated at or near the front.
- Caudal fin: the tail fin of a fish.
- Copepod: a large and diverse group of minute marine and freshwater crustaceans. They usually have an elongated body and a forked tail.
- Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans (whales, dolphins and porpoises).
- Fertilisation: the fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.
- Invasive: describes species introduced deliberately or unintentionally outside their natural habitats where they have the ability to establish themselves, invade, outcompete natives and take over the new environments.
- Invertebrates: animals with no backbone, such as insects, crustaceans, worms, molluscs, spiders, cnidarians (jellyfish, corals, sea anemones) and echinoderms.
- Larva: immature stage in an animal’s lifecycle, after it hatches from an egg and before it changes into the adult form. Larvae are typically very different in appearance to adults; they are able to feed and move around but are usually unable to reproduce.
- Pectoral fins: in fish, the pair of fins that are found on either side of the body just behind the gills. They are generally used for balancing and braking.
- Posterior: situated behind or at the rear.
- Spawning: the production or depositing of eggs in water.
- Swim bladder: also known as a gas bladder, an air-filled sac inside the body of many fish which is used to control buoyancy.
- Territory: an area occupied and defended by an animal, a pair of animals or a group.
IUCN Red List (April, 2014)
Universityof Minnesota - Iowa darter (April, 2014)
Montana Fish, Wildlife and Outdoors - Iowa darter (April, 2014)
University of Wisconsin Sea Grant Institute (April, 2014)
Center for Integrated Data Analytics - Iowa darter (April, 2014)