Iowa Darter - Etheostoma exile
There are about 100 species of small perches called darters. In Montana we have only one representative, the Iowa Darter. It is a native fish found in small streams and reservoirs in the plains region of our eastern drainage. During the spawning season, this species becomes one of Montana's most highly colored fish. Its maximum size is a little less than 3 inches (Brown 1971, Holton and Johnson 1996).
Iowa Darters are greenish or brownish with about eight saddle bands across the back and about nine to twelve dark blotches on the side. In breeding males these blotches become bluish-green with rust-red between them. The underside becomes orange and the first dorsal fin has a reddish band between a blue outer edge. The body is slender, the eye large, and the lateral line is incomplete (Brown 1971, Holton and Johnson 1996).
Iowa Darters range across much of south-central Canada and the north-central United States, in the St. Lawrence-Great Lakes, Hudson Bay, and Mississippi River basins.
Summary of Observations Submitted for Montana
Number of Observations:
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Not studied in Montana. Elsewhere, longer movements tend to be localized and related to breeding. During breeding they are found near shore of lakes and streams, then moving after breeding to deeper water in lakes or stream pools. Movements may occur from lakes into streams, probably over distances of several hundred meters (several hundred yards). In Michigan, movements to breeding areas began during mid-March to early April; males tended to initiate migration slightly before females (Winn 1958a, 1958b).
Iowa darters prefer clear slow-flowing streams with solid bottoms, although they have a wide range of tolerance for changes in water flow rates. They are also found in lakes and reservoirs, such as Nelson Reservoir east of Malta (Brown 1971). In Little Beaver Creek (Carter County), Iowa Darters were present during April to August in upstream and midstream pools and riffles that were characterized by cooler, clearer, lower water-velocity habitats, but were absent from downstream segments that were sampled, which had more riffles, reduced stream flows, and elevated late-summer water temperatures (to 30 C or more) (Barfoot and White 1999). Tempertures were 12-15 C in breeding pools of streams in Colorado during late April to early June, and the fish were found in masses of organic debris and slime on the pool bottoms; during the remainder of the year they were found under pebbles and in riffles in higher velocity water (Jaffa 1917). Breeding habitat in Michigan typically included the slow current of streams that contained some vegetation and submerged fibrous root banks. In lakes, Iowa Darters bred near shores over areas of fibrous root and organic debris. Sandy bottoms were often present in breeding habitats, males were never seen in muddy areas. After breeding, Iowa Darters moved to deeper waters of stream pools or lakes; in winter they could be found in thick organic debris and plants, to depths of 1.2 m (4 ft) (Jaffa 1917, Winn 1958a, 1958b).
Not studied in Montana. Food consists mostly of small crustaceans and aquatic insect larvae (Brown 1971). An examination of 100 stomachs (August 1968 to September 1969) from Sand Creek, Albany County Wyoming listed fly larvae in 54% of the stomachs, mayfly nymphs in 42%, caddisfly larvae in 15%, amphipods in 31%, and beetle adults, leaches, ostracods, copepods, snails, rotifers, and fish eggs in 1-4% of the stomachs; 12 stomachs were empty (Copes 1976). Overall, aquatic insects made up 64.7%, amphipods 14.6%, and animal remains 14.1% of the total volume. Stomachs contained an average of 4.2 food items. Larval Iowa Darters move to the surface or mid-strata of the water column near channel margins, where they feed on cladocerans and copepods (Turner 1921).
Not studied in Montana (but see Habitat comments). Iowa Darters were found in the stomachs of three Creek Chubs and one Brown Trout, and predaceous diving beetles attacked Iowa Darters while they were in fish traps (Copes 1976). In Sand Creek, Albany County Wyoming, the number of individuals per 100 ft of stream (800 ft sampled) during September were Age Class 0 = 9.3 (22.4%), Age Class 1 = 30.1 (73.4%), Age Class 2 = 1.6 (3.9%); respective Age Class biomass (grams) per 100 ft of stream were 4.2, 48.7, and 3.7. Age Classes 3 and 4 were rare.
Not studied in Montana. No parental care is given the young. Fish become brightly colored when spawning (Brown 1971). In Michigan (Winn 1958a), the reproductive period is April and May, when males establish territories. Males establish territories and guard an area of 30-60 cm diameter at the margin of a stream or near a lake shore. Size of reproductive females (Age Class 2) was 41-43 mm standard length. Females deposit 3-7 eggs per spawning in organic debris and fibrous mud banks, an average of 1619 eggs total are laid per female. Class 1 females (34-37 mm standard length) laid 550-962 eggs, Class 2 females (41-43 mm) laid 1404-1798 eggs, Class 3 females (46-47 mm) laid 1912-2048 eggs. Water-hardened eggs are 0.9-1.1 mm in diameter, and possess a single pale yellow oil globule and an opaque yolk (Simon and Faber 1987). Incubation is for 9 to 26 days in laboratory aquaria (Jaffe 1917, Winn 1958a, Simon and Faber 1987). Eggs are abandoned by the adults during incubation.
No management activities specific to Iowa Darter are currently occuring in Montana. Surveys to assess population status and life history throughout the state would be useful.
Threats or Limiting Factors
As with many small native stream fishes, Iowa Darters could be adversely effected by stream channelization, reductions to discharge, changes in water quality, and introductions of non-native predatory fishes.
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