Kyle R. Piller, Southeastern Louisiana University
Publication Date - April 2011
|Common Name:||Iowa Darter|
|Other Common Names:||Red-sided darter (Hoy 1883)|
|Scientific name:||Etheostoma exile|
|Wisconsin Synonyms:||Boleichthys exilis (Girard 1859; Hoy 1883)|
Etheostoma iowae (Jordan and Meek 1885; Pearse 1918)
Poecilichthys exilis (Greene 1935)
See Hubbs (1926) for complete synonymy
|Etymology:||Etheostoma - Greek, etheo, meaning strain or filter and stoma, meaning mouth|
exilis - Greek, slim or slender
The Iowa darter is a member of the perch family (Percidae). It was originally described as Boleichthys exilis by C. F. Girard (1859) from the upper Missouri River drainage in North Dakota. The origin of the common name, Iowa darter, is unknown. Due to similarity in body shape and the anteriorly curved lateral line, early researchers confused the Iowa darter with members of the Etheostoma subgenus Hololepis, none of which occur in Wisconsin. Taxonomic and nomenclatural confusion was clarified by Hubbs (1926) who provided a complete synonymy for the Iowa darter.
No comprehensive study of geographic variation in morphology has been conducted, and other studies of variation have been limited. Gosline (1947) examined meristic variation from 1,000 specimens from a single population in Michigan and noted that males tended to have more dorsal spines than females. Scott and Crossman (1973) compared populations from Ontario and Saskatchewan, and although sample sizes were small, some variation was noted, including slightly higher counts from populations from Ontario for dorsal spines, anal spines, and vertebrae. No Iowa darter subspecies are currently recognized.
There has been considerable controversy regarding the evolutionary relationships and systematic position of the Iowa darter. Based on morphology, both Page (1981) and Shaw (1996) placed the Iowa darter in the subgenus Boleichthys, whereas Bailey and Etnier (1988) placed it in the subgenus Oligocephalus, which includes other Wisconsin species such as the rainbow darter and mud darter. None of these studies included Wisconsin specimens in their phylogenetic analyses. Turner (1997) presented a third hypothesis based on mitochondrial DNA sequences and suggested that the Iowa darter is related more closely to members of the subgenera Ozarka and Oligocephalus than to the subgenus Boleichthys. Lang and Mayden (2007) independently analyzed mitochondrial and nuclear DNA sequence data for representatives of all darter subgenera and concluded that the Iowa darter was best classified as a member of the subgenus Oligocephalus.
The Iowa darter has an elongate, slightly laterally compressed body.
Body depth and head length go into standard length (SL) 4.8-5.5, and 3.5-3.8 times, respectively (Becker 1983). The snout is rounded, and the mouth is terminal and slightly oblique.
The upper jaw extends to just below the anterior margin of the pupil. The gill rakers are relatively short and stout. The Iowa darter possesses a small spine on the posterior portion of the opercle, and the gill membranes are broadly joined. The Iowa darter has ctenoid scales. The cheeks, opercle, nape, and belly are completely scaled, and the breast is partially scaled. The lateral line is curved upward anteriorly near the origin of the first dorsal fin and is incomplete, typically terminating near the origin of the second dorsal fin.
The Iowa darter does not possess a swim bladder (Simon and Faber 1987). The anal and first dorsal fins in males are longer than those of females (Winn 1958b). In Wisconsin, Iowa darters have 55-65 lateral line scales, of which 27-42 lack lateral line pores (Becker 1983). They also have nine (8-12) spines in the first dorsal fin, 11 (10-12) rays in the second dorsal fin, and five to six branchiostegal rays. The anal fin has two spines and eight (seven to nine) rays. Iowa darters typically have 37-38 (34-40) vertebrae (Bailey and Gosline 1955) and 48 chromosomes (Danzmann 1979).
Iowa darters have several alternating irregularly shaped dark and light blotches along their sides, a "teardrop" of pigment below each eye, and a checkered pattern on the caudal and second dorsal fins.
They lack saddles. Breeding males are brightly colored; their sides have bright red-orange blotches and darker greenish-blue blotches, and their belly is colored a bright reddish-orange.
Their first dorsal fin is bordered by a narrow blue band with submarginal bands of red and blue, and their anal fin also may be reddish orange.
The other fins lack bright chromatic pigments. Females and juveniles typically lack the bright chromatic pigments of breeding males and are usually mottled brown in appearance. However, the first dorsal fin of mature females often has coloration similar to but less striking than males.
In Wisconsin, the breeding Iowa darter is most similar to the rainbow darter and the mud darter. These two species have deeper and more robust bodies and possess red and blue pigmentation in the second dorsal fin, which the Iowa darter lacks. The Iowa darter has more than 50 lateral line scales versus 37-40 for the rainbow darter and 45-50 for the mud darter. The Iowa darter lacks saddles, which are prominent in rainbow and mud darters. Juveniles of many darters, including johnny, crystal, bluntnose, western sand, and least darters, are superficially similar to Iowa darters. However, Iowa darters can be differentiated by their two anal fin spines versus a single anal fin spine in the other species. For more details about the appearance and identification of the Iowa darter, see the website http://www.seagrant.wisc.edu/home/Default.aspx?tabid=604.
In Wisconsin, the Iowa darter reaches a maximum size of 68 mm SL (2.67 inches) (Lutterbie 1976). On average, northern Wisconsin populations (Florence, Forest, Marinette, and Langlade counties) of the Iowa darter grow slower and live longer, reaching age 4, than central Wisconsin populations (Portage, Marathon, Kewaunee, Shawano, Waupaca, Menominee, Clark, Wood, Door, and Trempealeau counties), which only reach age 3 (Lutterbie 1976; Table 1). Johnson and Hatch (1987) and Hatch (University of Minnesota, unpublished data) reported slightly higher growth for populations from Minnesota: 40-42 mm total length (TL) at age 1, 50-55 mm at age 2, and 60 mm at age 3. They also reported that females grew faster and lived longer than males and that few Iowa darters survived beyond their second spawning season (23-25 months). Copes (1970) determined that Iowa darters from Wyoming reached 39.2 mm TL at age 1, 53.0 mm at age 2, and 63.8 mm at age 3, and that females grew faster than males.
Table 1. Age and growth of northern and central Wisconsin populations of the Iowa darter (from Lutterbie 1976). Length values reported by Lutterbie (1976) were converted from standard length to total length using the conversion value of 1.20 reported by Becker (1983)
|Measure Total length (mm)||Estimated Total length (mm) at age|
The Iowa darter is distributed farther north than any other species in the genus Etheostoma (Becker 1983; Page and Burr 1991). It occurs throughout the northern third of the United States and the southern half of Canada in the Great Lakes, Mississippi River, and Hudson Bay basins (Page 1983).
The Iowa darter was introduced into the headwaters of the Colorado River, Colorado (Tyus et al. 1982; Woodling 1985); the Yampa River, Colorado; and Green River, Utah (Walford and Bestgen 2008) and in the San Juan River, New Mexico (Lee and Gilbert 1980; Tyus et al. 1982). The validity of the New Mexico record, however, has been questioned by Sublette et al. (1990)
In Wisconsin, the Iowa darter is an uncommon to common species that occurs primarily in the glaciated portions of the Mississippi River, Lake Superior, and Lake Michigan basins (Becker 1983).
Hoy (1883) reported that the Iowa darter occurred in the Rock and Fox rivers. Cahn (1927) found Iowa darters in Oconomowoc, Pine, and La Belle lakes (Waukesha County) in the Rock River drainage. Greene (1935) noted the occurrence of Iowa darters in all drainages in Wisconsin. He also reported that populations were relatively scarce in the Driftless Area in southwestern Wisconsin, a statement that has been corroborated by subsequent intensive field studies in this area (Becker 1966; Becker 1983; Fago 1992). Specimens are also known from the Mississippi River (Becker 1983; Fago 1992). Iowa darters occur in large lakes including Lake Winnebago and Lake Poygan (Winnebago County) and Lake Superior and Lake Michigan but are rare (Becker 1983; Fago 1992). More data on the distribution of Iowa darters within Wisconsin can be found at the website http://infotrek.er.usgs.gov/wdnrfish/map/index.
The Iowa darter is a habitat generalist and mainly occupies heavily vegetated streams and small rivers (3-25 m width), small lakes, and bog ponds (Becker 1983).
It is most frequently found along clear or tannic-stained, shallow, heavily vegetated reaches of the shorelines of lakes and their outlet streams (Eddy and Surber 1947; Becker 1983).
In a statewide distributional survey, Fago (1992) showed that the Iowa darter occurred in lakes (57%) more often than in streams or rivers (43%). Iowa darters occur most often in lakes with slightly acidic-neutral pH levels (6.0-7.0) and are generally absent below pH 6.0 (Rahel and Magnuson 1983). Tolerance of Iowa darters to extremes in temperature or to various pollutants has not been reported in the literature, although the water temperature preference of the Iowa darter is classified as warm (Lyons et al. 2009).
The microhabitat of the Iowa darter has not been studied thoroughly, but the species is most frequently collected in vegetated areas at depths less than 1.5 m over sand and gravel substrates (Becker 1983). Lyons (1987) noted that during summer and fall, adult Iowa darters in Sparkling Lake (Vilas County) were most abundant at depths less than 1 m but were also fairly common at depths of up to 5 m. They were often observed near rocks or logs but never under these structures. Young of the year and juveniles occupied deeper waters (2-4 m) among macrophytes in July and August. Moyle (1969) observed Iowa darters at depths of 5-6 m in Long Lake, Minnesota. Copes (1970) reported densities of young-of-the-year Iowa darters as high as 100/m2, but Lyons (1987) estimated much lower densities from Sparkling Lake. There, the density of young of the year ranged from 14-163/ha (0.0014-0.0163 m2) when the entire lake was considered and 0.01-0.13 m2 within the 6 m depth contour. Values for adults ranged from 3.3-53/ha (0.0003-0.0053/m2) for the entire lake and 0.003-0.04/m2 within the 6 m depth contour. Mahon and Balon (1977) reported that Iowa darters comprised 5.8% of the total number of individuals collected during a study of Long Pond, a lagoon on Lake Erie, but only 0.1% of the standing crop.
Larval Iowa darters occupy somewhat different habitats than older individuals. In Swamp Creek, northeastern Wisconsin (Wolf River Drainage), larval Iowa darters were collected in bottom detritus over sandy substrates, whereas in Lake Onalaska, part of Pool 7 of the Upper Mississippi River, larvae were captured downstream of beds of aquatic vegetation (Vallisineria and Elodea), and in the upper portion of the water column near the water's edge (Simon and Faber 1987).
Iowa darter populations are stable in Wisconsin but have declined in other areas of the Midwest. Iowa darter populations in northern Ohio (Trautman 1981; Phinney and Rice 1984) and Illinois (Smith 1968) have been greatly reduced in stream and lake systems that have been heavily influenced by agricultural influences and other anthropogenic modifications (Kuehne and Barbour 1983). The Iowa darter is considered endangered in Illinois (Illinois Endangered species Protection Board 1999).
Iowa darters spawn mainly in the spring. Lutterbie (1979) stated that Iowa darters in Wisconsin spawn from late April to mid-June. Cahn (1927) reported gravid females in June in Waukesha County and Lyons (Wisconsin DNR, 2002, personal communication) noted spawning activity in June in Vilas County. Forbes and Richardson (1920) and Winn (1958b) reported spawning in April and May in Illinois and Michigan, respectively, and Johnson and Hatch (1987) reported spawning from mid-April to mid-June in Minnesota. Copes (1970) noted that spawning occurred from late April through late July in Wyoming.
The most comprehensive study of the reproduction of Iowa darters was carried by Winn (1958a, b) in Michigan waters and in the laboratory. He found that Iowa darters migrated from deeper regions of lakes and streams to the shallow vegetated reaches for spawning. Males typically migrated before females. Male Iowa darters maintained and defended 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. In the laboratory, eggs were attached to algae and to the roots and leaf blades of the aquatic plant Vallisineria. 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.
Two studies have examined the fecundity of Iowa darters. Lutterbie (1976) reported that the ovaries of Wisconsin females comprised approximately 8.7% of the total body mass in April and 11.1% in June but declined to 1.1% in July, indicating the cessation of the spawning season. The relative mass of the ovaries remained at low levels in July and August but began to increase in September and October, as egg development began for the upcoming spawning season. At peak relative ovary mass in June, females were reported to hold both immature white (0.5 mm diameter) and mature orange (1.0 mm diameter) eggs. However, Simon and Faber (1987) suggested that these measurements of immature eggs were actually of the oil globules that had separated from the eggs rather than mature eggs themselves. The total number of eggs appeared to be a function of the age and size of the fish: age 1 - 429 (348-510); age 2 - 665 (312-970); and age3 - 934 (905-962) (Lutterbie 1976). Winn (1958b) reported a higher mean number of eggs for Iowa darters from Michigan: age 1 - 723 (550-992); age 2 - 1,619 (1,404-1,798); and age 3 - 1980 (1,912-2,048). These differences can be attributed to differences in the methods of enumeration. According to Lutterbie (1976) testicular development in males followed a similar seasonal pattern.
Several studies have examined aspects of Iowa darter development. Fish (1932) described and illustrated a 19.5 mm larval Iowa darter from Lake Erie. A more detailed analysis of developmental life history of the Iowa darter was conducted by Simon and Faber (1987). They studied populations from Quebec (Lac Henry), but additional material was analyzed from northern Illinois (Druce Lake) and from Wisconsin including the Upper Mississippi River and Hope Lake (Jefferson County). Winn (1958a, 1958b), studying Michigan populations, and Simon and Faber (1987) studying Illinois populations, noted that spawned eggs of the Iowa darter averaged 1.1 mm diameter (0.9-1.3 mm). In the laboratory, Jaffa (1917) reported that the developmental time of Iowa darter eggs from Colorado was 18-26 days at 13-16°C and that newly hatched darters were 3.4 mm SL. Simon and Faber (1987) reported a hatching size of 3.6 mm TL and stated that 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 approximately 20 mm TL. Larval pigmentation patterns superficially resembled those of larval yellow perch.
Iowa darters produce and react to alarm pheromones. Smith (1979) conducted laboratory experiments and showed individual Iowa darters exhibited fright responses, including freezing in place followed by decreased activity for up to an hour, when exposed to skin extracts of other Iowa darters. Fright responses of similar character occurred following exposure to muscle extracts, but the degree of response was significantly less. Histological examination of muscle and skin tissues indicated that the skin contained large non-mucous cells that were likely involved in secreting the alarm pheromones that elicited the fright responses. Chivers et al. (1995) found that Iowa darters decreased their reproductive activities in the presence of northern pike, a predator. Wisenden et al. (1995) also showed in laboratory experiments that Iowa darters released alarm pheromones to warn other members of the species of the presence of a predator. In response to these releases, other Iowa darters suppressed exploratory behavior and displayed more alert postures. Copes (1970) observed Iowa darters darting short distances (0.2-0.6 m) when alarmed, often darting and burrowing into debris or detritus. McPherson et al. (2004) documented that fright responses of Iowa darters were suppressed when exposed to metal contamination.
Emery (1973) studied the daytime and nighttime habits of Iowa darter and other species in Ontario. He noted that Iowa darters were routinely observed in shallow water (0.5-1.5 m) over sandy bottoms near fallen or submerged woody debris. He determined that Iowa darters fed most actively during the daytime and could be easily approached. At night, the species was cryptic and retreated to rock crevices or within and under submerged logs.
Iowa darters exhibit behaviors that enable them to survive some harsh physio-chemical conditions. Magnuson et al. (1985) observed the emigration of Iowa darters from Mystery Lake, Vilas County, into an outlet stream in late fall and early winter, followed by immigration back into the lake in late spring. The authors suggested that the movements were a behavioral adaptation to avoid winterkill. Iowa darters migrated while dissolved oxygen levels in the lake were relatively high; during mid to late winter dissolved oxygen dropped below <4 mg/L, a level stressful to most fish species. Previous studies, however, have reported that Iowa darters in a Michigan winterkill lake survived very low oxygen levels (<0.2 mg/l) (Becker 1983).
Hatzenbeler et al. (2000) surveyed the littoral zone of five northern Wisconsin lakes to assess seasonal changes (spring, summer, and fall) in species abundance. They noted that the abundances of several species, including yellow perch, pumpkinseed, and rock bass, were significantly different among seasons, but that numbers of Iowa darters and other benthic fishes remained fairly constant, apparently because they were able to withstand a range of physio-chemical conditions. Lyons (1987) indicated that the depth distribution of Iowa darters in Sparkling Lake did not change from June to October but implied that the high relative abundance of cover and vegetation in shallow areas compared to deeper areas may have influenced their distribution.
The Iowa darter eats primarily invertebrates. Pearse (1918) reported that the diet of Iowa darters from Dane County was comprised of amphipods (58%), midge larvae (Chironomidae) (21%), and beetle larvae (16%). Cahn (1927) noted that Iowa darters from Waukesha County consumed copepods and nymphs of mayflies and stoneflies. Moyle (1969) studied Iowa darters from Minnesota and determined that the bulk of their diet was comprised of midwater organisms such as amphipods (Hyalella spp.) and dipteran larvae (Palpomyia spp.). Turner (1921) reported that juveniles from Ohio ingested primarily copepods, cladocerans, and ostracods but that they switched to larger food items including mayflies, amphipods, and midges as they grew older. In Wyoming, Copes (1970) documented that aquatic insects, including dipteran and caddisfly larvae and mayfly and dragonfly nymphs, comprised 64.4% of the diet. The remaining portion of the diet consisted of amphipods (14%), unknown animal remains (14.4%), and leeches, ostracods, gastropods, and rotifers (6%). Aquarium-held Iowa darters ingested small sucker fry (Catostomidae), small guppies (Poecilia reticulata), mosquito larvae, fairy shrimp, Daphnia, copepods, and frozen brine shrimp (Copes 1970; Smith 1981). Keast and Fox (1990) showed that Iowa darters in Ontario ingested different groups of invertebrates as the resource base changed. In May, their diet primarily consisted of dipterans, while in August chironomids comprised 86% of stomach contents. In a study conducted in an Ontario Lake, 78% of Iowa darters collected from beneath the ice contained no food (Keast 1968), and they had become very thin by February and March (Keast 1968). Individuals that had fed contained, in order of percentage by volume, snails, amphipods, damselfly nymphs, mayfly nymphs, chironomid larvae, and planktonic crustaceans. Some prey types that were judged to be important in the summer (stonefly and dragonfly nymphs, caddisfly larvae, and hemipterans [true bugs]) were not found in Iowa darter stomachs collected in the winter.
The Iowa darter co-occurs with a wide variety of species. Cahn (1927) reported that the Iowa darter was commonly associated with the johnny darter, rainbow darter, and river shiner in the southeastern portion of Wisconsin. Cahn's identification of the river shiner from this area, however, is questionable. In a statewide analysis of fish assemblage composition, Lyons (1996) showed that the Iowa darter was most often found with yellow perch and golden shiners in the northern portion of the state. In northern Minnesota, Schlosser and Kallemeyn (2000) reported that Iowa darters were most often associated with central mudminnows, pearl dace, and blacknose shiners. Stream and river fish surveys by the Minnesota Pollution Control Agency indicated that the following seven species occurred at more than half of the sites where Iowa darter were captured: white sucker (84%), johnny darter (67%), fathead minnow (66%), central mudminnow (62%), common shiner (58%), blacknose dace (52%), and brook stickleback (51%) (Konrad Schmidt, 2008, Minnesota DNR, personal communication). Harvey (1978) surveyed the lakes on Manitoulin Island, Ontario, in Lake Huron and reported that the Iowa darter most often occurred with the yellow perch but also was commonly associated with the northern pike, bluntnose minnow, rock bass, and smallmouth bass.
The Iowa darter has no direct commercial or sport fishery value, but it is an important component of aquatic ecosystems. Iowa darters are prey for larger predatory fish including bowfin (Scott and Crossman 1973), northern pike and largemouth bass (Soupir et al. 2000), burbot (Hanson and Quadri 1980), creek chubs and brown trout (Copes 1976), and walleye (Lyons and Magnuson 1987) and birds such as the white pelican (Findholt and Anderson 1995). Iowa darters are intolerant of a variety of habitat modifications, including loss of macrophytes, and of pollutants, and are considered a sensitive indicator of environmental quality (Lyons 1992). Iowa darters make excellent aquarium fishes, although their spawning colors fade quickly when they are removed from their natural habitats (Katula 1996, 2000). Like most other darters that inhabit the state, they can be maintained on a diet of small invertebrates, such as bloodworms.