Etheostoma exile

Iowa darter
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Family:	Percidae
Genus:	Etheostoma
Species:	E. exile
Binomial name
Etheostoma exile (Winn, 1958)

The Iowa darter (Etheostoma exile) is a species of freshwater fish in the perch family (Percidae) of order Perciformes. The Iowa darter, along with about 17 other species of darters, is native to the lakes and streams of Iowa.

In some parts of its range, the Iowa darter is also known as the weed darter, red-sided darter, or yellowbelly. The Iowa darter, like many other darters, are about 2-3 in (51–76 mm) in length and may be easily confused with other darters of similar color.

Range

Native distribution of the Iowa darter extends north to central Canada, east to New York, and south to central Illinois, and the species is particularly common in the western Great Lakes drainages and Iowa. Western populations are distributed patchily in Colorado, Wyoming, Montana and Alberta. They are native in Colorado only in the South Platte River drainage, but recent research has also placed them in the Yampa River (Colorado) and the Green River (Utah).^[2]

Description

The Iowa darter has a very slim, small body. Its common length is around 5.5 cm and its maximum age is three years.^[3] It has a small mouth and snout with scaled opercles and cheeks, two dorsal fins, one which is a spinous-rayed fin and another soft-rayed fin. Its caudal fin is squarish and the pectoral fins and pelvic fins are located close to each other behind the gills. It has an anal fin with two (rarely one) spines and an incomplete lateral line. The male and female Iowa darters have different color patterns. During breeding, males are olivaceous dorsally with darker splotches across the top of their backs. Their sides are red with blue rectangular blotches and ventrally they are whitish with a dark wedge shape below the eyes. The bottom half of the spiny dorsal fin has blue spots between the spines and above the spots is a succession of three bands, orange on the bottom, clear in the middle, and then blue on the outside. Females are olive-brown dorsally with darker splotches across the top of their backs. Their sides are mottled and fade into a silver-white on their bellies. They also have a dark wedge shape below the eyes that is well developed.^[4]

Habitat and habits

Iowa darters prefer cool, clear water over a sand or organic-matter substrate.^[4] Iowa darter lacks a swim bladder, so it sinks to the stream or lake bottom. To move around, it makes short dashes of astonishing speed (hence the name), often faster than the human eye can follow. The darter can zip along stream and lake substrate looking for food using less energy than other fish, which would keep floating up off the bottom.^[5]

Diet

The Iowa darter eats copepods, water fleas, and midge and mayfly larvae it finds in underwater vegetation. It has never been found in the stomach of any fish-eating animal because it is too quick to catch.^[5]

Conservation status

Iowa darters are considered vulnerable due to decreasing abundance and distribution. They appear to be decreasing in distribution over the last decade, and the limiting factor seems to be their habitats. This may be due to increasing turbidity limiting their preferred habitat.^[6]

Reproduction

Iowa darters spawn mainly in the spring. They migrate from deeper regions of lakes and streams to the shallow, vegetated reaches for spawning. Males typically migrate before females, and maintain and defend small territories near undercut banks with rooted vegetation. Smaller males, however, were promiscuous, did not defend territories, and were mobile, moving from place to place in search of females. When a female entered a male's territory, the male courted the female by swimming around her until she positioned herself near algae or rooted vegetation. The male mounted the female and positioned himself with his pelvic fins in front of her dorsal fin. The anal and caudal fins of the male were placed on the same side of the female. Most spawning occurred at depths of 10–40 cm on fibrous roots beneath slightly undercut banks, although some eggs were laid directly on sand or on roots or other plant materials on sand. During each spawning act, three to seven eggs were deposited. Following the completion of spawning, the eggs received some protection in that by continuing to maintain his territory, the male indirectly guarded the eggs. Females mated with several males, then returned to deeper habitats following spawning.^[7]

Lifecycle

The spawned eggs of the Iowa darter average around a 1.1 mm in diameter. Their developmental time is around 18–26 days at 13-16°C and the newly hatched darters are around 3.4 mm in standard length. The hatching size is around 3.6 mm total length (TL), and most major structural features, including the pectoral fin, first dorsal fin, second dorsal fin, and the branchiostegal rays were formed when the larvae were between 7.7 and 9.1 mm TL. Much of the lateral line sensory system was formed when the larvae reached about 20 mm TL.^[8]

Etymology

The genus name, Etheostoma, is from the Greek etheo meaning strain or filter and stoma meaning mouth. The species name, exile, also Greek, means slim or slender.^[8]

References