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Sugar Loaf Creek, tributary of Caddo River, Ouachita River system, on. U.S. Highway 70, in Township 4S, Range 22W, Hot Spring County, Arkansas (Hubbs and Black 1941).
Etymology/Derivation of Scientific Name
Etheostoma, from the Greek etheo, “to strain,” and stoma, mouth” (Pflieger 1997); radiosus – referring to the large number of soft dorsal rays (Hubbs and Black 1941).
Variation and systematics of Etheostoma radiosum were reviewed by Matthews and Gelwick (1988) who recognized three subspecies previously named by Moore and Rigney (1952): E. radiosum radiosum (inhabiting the Ouchita and Little rivers, Arkansas and Oklahoma), E. r. paludosum (Kiamichi, Boggy and Washita rivers, Oklahoma), and E. r. cyanorum (Blue River, Oklahoma). Echelle et al. (1975) analyzed variability in lactate dehydrogenase and esterase isozymes in Etheostoma radiosum and compared to patterns of morphological variability described by Moore and Rigney (1952).
Poecilichthys whipplii radiosus Hubbs and Black 1941:10-14.
Maximum size: 85 mm TL (Page and Burr 1991).
Coloration: Vertical blotches on sides of body most distinct posteriorly; a black spot at upper margin of pectoral fins (Hubbs et al. 2008). Page and Burr (1991) described coloration of species: short dark bars (rear bars long) along side, cut into upper and lower halves by yellow lateral line; body olive to tan above, 8-10 dark saddles; body white to orange below; black teardrop present; dorsal, caudal, and anal fins with blue edge and middle red band (faint on female); on large males, branchiostegal membranes orange and pelvic fins blue. Scalet (1973b) noted that color of females fades as breeding season approaches, while colors of the male intensify; in males, the humeral spot and the anteriormost saddle on the dorsal portion of the body become brilliant blue-green, the blue-green color of the pelvic fins intensifies and pelvic fins are tipped with orange, the breast and belly become bright orange, and colors of other fins and general body surface intensify.
Counts: Anal fin spines 2; more than 6 pored lateral line scales; less than 77 scales in lateral line (Hubbs et al. 2008); 47-66 (usually 52-61) lateral scales (Page and Burr 1991).
Body shape: Body cross section oval; body depth contained in standard length less than 5 times; pectoral fin shorter than head, not reaching anus; head profile rounded, profile in front of eye less than 45 degrees; snout not extending beyond upper lip; upper jaw not extending as far as to below middle of eye (Hubbs et al. 2008).
External morphology: Gill membranes rather widely joined across the isthmus; lateral line straight; scales on belly normal; preopercle smooth or weakly serrated (Hubbs et al. 2008). Genital papilla of female is long and conical (Page 1983). During the breeding season, males develop conical breeding tubercles located in the ventral portion of the body, extending from just behind pelvic fin origins to the anal fin origin (Scalet 1973b).
Distribution (Native and Introduced)
U.S. distribution: Primarily found in Red River tributaries in Oklahoma and Arkansas (Hubbs and Black 1941; Hubbs et al. 2008). Matthews and Gelwick (1988) and Moore and Rigney (1952) recognized three subspecies of Etheostoma radiosum: E. radiosum radiosum (inhabiting the Ouchita and Little rivers, Arkansas and Oklahoma), E. r. paludosum (Kiamichi, Boggy and Washita rivers, Oklahoma), and E. r. cyanorum (Blue River, Oklahoma).
Texas distribution: Red River (Hubbs and Black 1941; Hubbs et al. 2008).
Abundance/Conservation status (Federal, State, NGO)
Special Concern (Texas; Hubbs et al. 2008). Currently Stable (Warren et al. 2000) in the southern United States. Etheostoma radiosum widespread and abundant (Page 1983). Riggs and Bonn (1959) reported collection of four E. radiosum specimens from Butcher Pen Creek (Lake Texoma), Johnston County, Oklahoma, during the collection period from 1948-1958.
Macrohabitat: Streams (Scalet and Platania 1980); creeks, small to moderate-sized rivers (Page and Burr 1991).
Mesohabitat: Etheostoma radiosum inhabits a variety of habitats ranging from high gradient streams to more sluggish lowland streams; apparently preferring riffle areas of gravel-bottoms streams with moderate to high currents (Scalet and Platania 1980). In the Blue River, Oklahoma, E. r. cyanorum primarily associated with clear, flowing, rocky-bottomed raceways in the upper two-thirds of the river system: adults exhibited very little movement within the stream, while larval and young-of-year fish exhibited stream movement; postlarval fish were found in quiet water or pool areas of the stream; with increase in size, fish moved into progressively swifter water, and were found in raceway areas of the stream (adult habitat) at approximately 25 mm TL (Scalet 1973a). Collected from both isolated and connected pools in Cucumber Creek (third-order, upland stream) in the Mountain Fork drainage (Little River system), Oklahoma (Taylor 1997). Taylor (2000) sampled riffle and pool habits at upland localities in the Little River system and found E. radiosum to be associated with riffles. Laboratory testing indicated that E. r. cyanorum does not actively seek a particular thermal regime, but moves merely to avoid adverse conditions, and probably makes little use of temperature as a cue in habitat selection (Hill and Matthews 1980).
Spawning season: E. r. cyanorum spawns February to May, but mainly between mid-March and mid-April (Scalet 1973b).
Spawning habitat: E. r. cyanorum select small (3-5 mm in diameter) areas of gravel located in moderate current portions of raceway sections of the stream for spawning (Scalet 1973b). Protolarvae are passively swept into quiet water areas of the stream after hatching in raceway sections, or small bits of gravel on which eggs are attached may be carried by the water current into pool or quiet water areas prior to hatching (Scalet 1973a).
Spawning behavior: Spawning occurred in daylight hours, but not at night; male will follow and nip at the female while displaying brightly colored fins; when ready to spawn, the female will partially bury herself in the gravel or sand substrate, after which the male mounts her and the pair vibrate releasing eggs and sperm; female will move to another area where the process is repeated, sometimes with either the original male or another (Scalet 1973b; Page 1983).
Fecundity: Scalet (1973b) reported that peak gonadal development for E. r. cyanorum occurred in March, April and May, at which time the ovaries of females constituted approximately 10-15% of the body weight; fecundity was low, ranging from 51-270 mature eggs per female (based on counts from 11 specimens ranging from 35-55 mm SL) depending on size; fertilized eggs yellowish in color, spherical, transparent, demersal and adhesive, range in size from 1.2-1.5 mm; eggs laid singly or in clusters of up to 12.
Age/size at maturation: E. r. cyanorum reaches sexual maturity and spawns at 1 year old (Scalet 1973b).
Migration: Scalet (1973a) observed a type of migration in the Blue River proper (Oklahoma); just after spawning, large numbers of adults were found congregating in thick stands of Myriophyllum heterophyllum (water milfoil) where food was abundant, just after spawning; almost all individuals in these areas were completely spent, while individuals collected in spawning areas only a short distance away were still in spawning condition; apparently adults moved to areas with abundant food post-spawn.
Growth and population structure: Males slightly larger than females of the same age (Scalet 1973b). Scalet (1973a) reported approximately 2.7 adults present per square meter of raceway in the Blue River, Oklahoma study area.
Longevity: Up to 4 years (Scalet 1972, 1973b).
Food habits: Goldstein and Simon (1999) listed first and second level trophic classifications for this species as invertivore and benthic, respectively; main food items include crustaceans, mayfly and other insect larvae. In Glover Creek, Oklahoma, the diet of E. r. radiosum consisted primarily of aquatic insect larvae, especially dipterans, although a wide variety of other organisms were eaten; fish apparently fed selectively as frequency of major food items shifted noticeably between seasons; juveniles and adults diets differed significantly (Jones and Maughan 1989). In the Blue River, Oklahoma, diet of E. r. cyanorum adults consisted primarily of aquatic insect larvae and naiads (Tendipedidae, Baetidae, Hydropsychidae, Ephemeridae, and Simuliidae); young fish fed primarily on copepods and cladocerans; when fish reached approximately 16 mm TL the primary source of food consisted of ephemerids and dipteran larvae; fish from 22-30 mm TL fed mainly on small ephemerids, dipteran larvae, hydropsychids and baetids; both adults and juveniles were selective feeders (Scalet 1972). Scalet (1974) reported presence of four E. r. cyanorum eggs in two daters of the same subspecies, but noted that this predation was accidental or of little importance. In a study under laboratory conditions, Linder (1958) reported that E. radiosum ate their own eggs.
Phylogeny and morphologically similar fishes
Etheostoma radiosum differs from E. artesiae (redspot darter) in that no discrete red or yellow spots are present on side of body, and the vertical blotches on sides of body are most distinct posteriorly; E. artesiae has discrete red (in males) or yellow spots (in females) on side of body, and the vertical blotches on sides of body are usually not prominent (Hubbs et al. 2008).
Hybridization between Etheostoma spectabile and E. radiosum occurs in the Blue River, Oklahoma (Page 1983), and hybridization between these two species has been studied (Linder 1955, 1958; Branson and Campbell 1969; Echelle et al. 1974; Hubbs 1959, 1967; Mendelson 2003a, 2003b).
Scalet (1971) reported the following parasites from Etheostoma radiosum: Illinobdella moorei, a piscicolid leech; Crepidostomum cooperi, a digenetic trematode; and Uvulifer ambloplitis, the black-spot or black grub.
Commercial or Environmental Importance
Scalet (1974) examined twenty possible predator fishes of E. r. cyanorum and found no evidence of predation on either adult, juvenile, larval or egg stages, with the exception of four eggs eaten by two orangebelly darters.
Matthews et al. (2006) reported that this species was used successfully in a modular experimental riffle-pool stream system
Branson, B.A., and J.B. Campbell. 1969. Hybridization in the darters Etheostoma spectabile and Etheostoma radiosum cyanorum. Copeia 1969(1):70-75.
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Echelle, A.A., J.R. Schenck, and L.G. Hill. 1974. Etheostoma spectabile – E. radiosum hybridization in Blue River, Oklahoma. American Midland Naturalist 91(1):182-194.
Goldstein, R.M., and T.P. Simon. 1999. Toward a united definition of guild structure for feeding ecology of North American freshwater fishes. pp. 123-202 in T.P. Simon, editor. Assessing the sustainability and biological integrity of water resources using fish communities. CRC Press, Boca Raton, Florida. 671 pp.
Hill, L.G., and W.J. Matthews. 1980. Temperature selection by the darters Etheostoma spectabile and Etheostoma radiosum (Pisces: Percidae). American Midland Naturalist 104(2):412-415.
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Hubbs, C. 1967. Geographic variations in survival of hybrids between Etheostomatine fishes. Bulletin of the Texas Memorial Museum 13:1-72.
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Jones, R.N., and O.E. Maughan. 1989. Food habits of the juvenile and adult orangebelly darter, Ethestoma radiosum, in Glover Creek, Oklahoma. Proc. Okla. Acad. Sci. 69:39-43.
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Mendelson, T.C. 2003b. Sexual isolation evolves faster than hybrid inviability in a diverse and sexually dimorphic genus of fish (Percidae: Etheostoma). Evolution 57(2):317-327.
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Riggs, C.D., and E.W. Bonn. 1959. An annotated list of the fishes of Lake Texoma, Oklahoma and Texas. The Southwestern Naturalist 4(4):157-168.
Scalet, C.G. 1971. Parasites of the orangebelly darter, Etheostoma radiosum (Pisces: Percidae). Journal of Parasitology 57(4):900.
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Scalet, C. G. 1973a. Stream movements and population density of the orangebelly darter, Etheostoma radiosum cyanorum (Osteichthyes: Percidae). Southwestern Naturalist 17:381-387.
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Scalet, C.G. 1974. Lack of piscine predation on the orangebelly darter, Etheostoma radiosum cyanorum. American Midland Naturalist 92(2):510-512.
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