Etheostoma cyanorum ( Moore and Rigney, 1952 )

Matthews, William J. & Turner, Thomas F., 2019, Redescription and Recognition of Etheostoma cyanorum from Blue River, Oklahoma, Copeia 107 (2), pp. 208-218 : 211-214

Etheostoma cyanorum ( Moore and Rigney, 1952) , elevated to species

Blue River Orangebelly Darter

Figures 2 , 3 ; Tables 1, 2; Supplemental Table A

Holotype.— UMMZ 161366 , holotype of Poecilichthys whipplii cyanorum , adult breeding male, 68 mm SL, designated by Moore and Rigney (1952), collected by Moore in 1949 in Blue

River at State Hwy 99 north of Connerville , Johnston County, Oklahoma ( Fig. 2 ) .

Paratypes.— Paratypes include 329 individuals collected by Moore or students from the Blue River drainage (museum acronyms and catalog numbers, Moore and Rigney, 1952: p. 10) .

Diagnosis.— Etheostoma cyanorum differs from E. radiosum by their allopatric distribution, with E. cyanorum known only from Blue River and tributaries, versus E. radiosum occupying tributaries of Washita River west of Blue River and all drainages eastward from the Clear Boggy to the upper Ouachita and Little Missouri in southwest Arkansas. Etheostoma cyanorum differs from E. radiosum in having all assayed mtDNA haplotypes not shared with E. radiosum , lower counts of unpored lateral line scales, higher counts of pored lateral line scales, and a wider interorbital distance. Etheostoma cyanorum can be distinguished by a deeper and wider head from E. radiosum in all Oklahoma drainages, and in most but not all drainages in Arkansas. Nuptial males of Etheostoma cyanorum differ from nuptial E. radiosum in the geographically closest drainages (Washita, Clear Boggy, Muddy Boggy, and Kiamichi) by a solid blue distal band in the spinous dorsal ( Fig. 3C ), compared to the distal blue band in those populations of E. radiosum (¼ E. r. paludosum of Moore and Rigney) having an appearance of blue ‘‘dots’’ or ‘‘spots’’ bordered in white, between clear or orange tips of the fin spines.

Description.— Etheostoma cyanorum is a moderately large darter of the clade Vexillapinna ( Near et al., 2011) and subgenus Oligocephalus ( Lang and Mayden, 2006) , averaging about 45 mm standard length; largest specimens about 70 mm SL. Holotype meristics, morphometrics, and colors in Moore and Rigney (1952). Meristics and morphometrics from Moore and Rigney (1952) and Gelwick and Matthews (1988) compared in Supplemental Table A (see Data Accessibility). Snout decurved and blunt in large adults, less so in smaller individuals. Moore and Rigney (1952) noted, for unusually large holotype, ‘‘back is little elevated, sloping in almost a straight line to the caudal peduncle.’’ In smaller individuals, head slopes upward at about a 208 angle from eye to occiput with pronounced hump at the occiput, dorsum then elevated about 158 from horizontal posteriorly to origin of dorsal fin, beyond which body is relatively uniform depth to origin of soft dorsal and anal fins, beyond which dorsum and caudal peduncle taper slightly to caudal base. Lateral line scales average 55; unpored lateral line scales average 5.9; pored lateral line scales average 49. Dorsal spines average 10.4; dorsal soft rays average 13.6; anal-fin soft rays 7 to 8; pectoral-fin rays typically 12; pelvic-fin rays invariant at 6. Gill rakers average 10. Average measurements (in thousandths of standard length): predorsal length 345; body depth 205; caudal peduncle depth 116; head length 269; head depth 170; interorbital width 54; eye diameter 67; gape width 73; snout length 69. Distribution of scales on head and body in Moore and Rigney (1952); tuberculation in Collette (1965); natural history and ecology in Scalet (1971).

Coloration.— Coloration as in Moore and Rigney (1952) and Scalet (1971), except nuptial male E. cyanorum have more yellow or yellowish-orange on cheeks and lower sides of head and body ( Fig. 3A ) than does E. radiosum , particularly E. radiosum in Ouachita River drainage where coloration is more reddish-orange ( Matthews and Gelwick, 1988). Reproductive females drab in comparison to males; light yellow on cheeks and pectoral, anal, and caudal fins, and light orange below the opercle ( Fig. 3B ). Distal blue bar in spinous dorsal of nuptial male E. cyanorum solid band passing across the membranes and including the spine tips, except the two posterior spines ( Fig. 3C ).

Snout shape not diagnostic.— Moore and Rigney (1952) considered blunt snout diagnostic of E. r. cyanorum , but this is strongly influenced by body size. Table 1 of Moore and Rigney showed snout length of E. cyanorum went fewest times into head length compared to other subspecies,

suggesting a longer, not shorter, snout length. Matthews and Gelwick (1988, their table 5) also found that specimens from Blue River had longest mean snout length, pointing out that a ‘‘blunt’’ snout is not necessarily equivalent to a ‘‘short’’ snout if the snout is greatly curved downward and is properly measured from eye to snout tip (on an angle) per Hubbs and Lagler (1964). Indication that a ‘‘blunt’’ snout was diagnostic ( Moore and Rigney, 1952) was based on the large holotype (68 mm SL) described as ‘‘very robust,’’ with a head ‘‘quite blunt’’ and ‘‘sharply decurved from the eyes to the snout tip.’’ The holotype ( Fig. 2 ) is larger than any of 300 þ typically sized individuals evaluated by Matthews and Gelwick (1988; mean ¼ 45, maximum ¼ 64 mm SL). The holotype, although faded ( Fig. 2 ), is well preserved, with extremely downturned snout, blunt face, and deep body per Moore and Rigney, but their description only applies to very large specimens. Of six nuptial males from Blue River August 2017, ranging 47 to 60 mm SL, only the largest (upper right in Supplemental Figure B; see Data Accessibility) approaches bluntness of snout described by Moore and Rigney (1952). For 11 males ranging 35 to 69 mm SL collected in the upper Blue River on 24 September 1994, larger individuals had a significantly more obtuse angle (regression of AAP on SL, P ¼ 0.0015) between the horizontal axis of the body and the snout ( Fig. 4 ). The holotype had a wider AAP (648) between axis of the body than any specimens we examined ( Fig. 4 ), confirming that the holotype was an individual with an unusually blunt snout.

Allometry.— Three other head or body traits have strong to moderate allometric trends. In Supplemental Figure C (see Data Accessibility), 26 male E. cyanorum used in Matthews and Gelwick (1988) from three locations in Blue River, traits (parts per thousand of standard length) are plotted against standard length with a trendline added by the Excel linear trendline function for significant regressions. Larger males had relatively shorter snouts (regression P ¼ 0.068), consistent with the results in the section above, deeper bodies (regression P ¼ 0.011), and a weak, but non-significant trend for a deeper caudal peduncle (Supplemental Figure C; see Data Accessibility).

Distribution.— Etheostoma cyanorum is known only from the Blue River drainage in southcentral Oklahoma, a tributary of Red River. It is most abundant in the upper, spring-fed, rocky portions of the drainage, and in some small tributary creeks,

but is scarce or absent in lower, muddy portions of the drainage closer to Red River.

Etymology.— The specific name ‘‘ cyanorum ’’ (¼ ‘‘of the Blues’’ referring to Blue River) was suggested for the subspecies, on advice from R. M. Bailey ( Moore and Rigney, 1952), to reflect restriction of this form to Blue River and its tributaries. Linder (1955) and Echelle et al. (2015) referred to it as the ‘‘Blue River Orangebelly Darter,’’ but Near et al. (2011) called it ‘‘Blue Darter.’’ We follow Linder (1955) and Echelle et al. (2015) and recommend the common name ‘‘Blue River Orangebelly Darter,’’ because E. cyanorum is not predominantly blue in coloration. This common name aligns with the practice of referring to other fishes in Oklahoma in a drainage-specific manner, including Red River Pupfish ( Cyprinodon rubrofluviatilis ), Red River Shiner ( Notropis bairdi ), and Arkansas River Shiner ( Notropis girardi ).

Figures

FIG. 2. Holotype of Etheostoma cyanorum, as P. radiosus cyanorum (Moore and Rigney, 1952). Photograph courtesy of the Fish Division, University of Michigan Museum of Zoology.

FIG. 3. (A) Male E. cyanorum, 63 mm SL, in nuptial color, from mainstem Blue River, 1.7 km west-northwest of Connerville, OK, 30 March 2018 (WJM 3645; OMNH 86859); (B) female E. cyanorum, 41 mm SL, same collection (OMNH 86860). Location: 34827.0670N, 96839.3270W. Photographs by N. Lang. (C) Detail of distal color band in nuptial male from same collection, same date (OMNH 86861). Photograph by WJM.

FIG. 4. Angle of the anterior profile for 11 male E. cyanorum, from Blue River in September 1994, with significant trendline, and the holotype (indicated by arrow; not included in regression or in trendline).