Flagfin sucker (Vexillichthys atripinnis) replaces blackfin sucker (Thoburnia atripinnis) which resembles hog sucker (Hypentelium)

NEWS - Blackfin sucker (Thoburnia atripinnis) is more closely related to the hog suckers (Hypentelium) than to the rustyside suckers (Thoburnia) and its occurrence in the Barren River, Kentucky, is separate from the true Thoburnia, but its morphology is not like Hypentelium, so Jonathan Armbruster of the Auburn University Museum of Natural History describes it as a flagfin sucker (Vexillichthys atripinnis).

Vexillichthys can be distinguished from all other Catostomids by the presence of thin black stripes on the body and a large black mark on the anterodistal part of the dorsal fin. Hypentelium and Thoburnia may have stripes, but they are faint and the dorsal saddle is darker than the stripes (vs. the stripes are darker than the saddle in Vexillichthys).

Hypentelium has dark markings on the dorsal fin, but the fin has a band or spot rather than one large black area on the anterodistal part of the fin and the fin remains are hyaline. Vexillichthys can be further separated from Thoburnia by the absence of a broad rust-colored lateral line. Minytrema also has dark stripes, but these consist of distinct spots (vs. continuous stripes).

Some species of Moxostoma previously considered Scartomyzon may also have stripes, but they are not as strong as Vexillichthys and there is little black on the anterodistal edge of the dorsal fin (vs. a broad area).

Vexillichthys is also unique in the development of pads at the distal ends of the anterior unbranched rays of the pectoral fins as well as the anterior part of the first and sometimes the second branched ray (other fishes may have thickened skin in this area, but lack the distinct pads).

Osteologically, Vexillichthys can be diagnosed by two skull characteristics: the lateral dermethmoidal laminae are angled anteriorly (vs. laterally in T. rhothoeca or posteriorly as in Hypentelium and Moxostoma); The narrowest part of the lateral ethmoid when viewed ventrally is much smaller than the length of the anterolateral process (almost the same in T. rhothoeca and Hypentelium).

V. atripinnis is found only in the upper Barren River in Kentucky and Tennessee, USA, in headwater streams (1.5-9 m wide) with alternating pools and rapids. The streams are clear with limestone, shale, and siltstone substrates. Juveniles are found in pools (0.3-1 m deep) often in groups on gravel.

Adults are collected along the shore or in pools (1.0-1.5 m deep) and crevices in bedrock. Adults are associated with bedrock ledges, boulders, rock slabs, and root clumps. They feed on chironomids, cladocerans, copepods, ostracods, simuliids, melgaloptera, and trichoptera.

Males congregate in riffles several weeks before the arrival of the spawning females (females are usually in pools). Egg size is 1.7–2.5 mm and ranges from 1,070 to 1,755 eggs per female. Maximum lifespan is five years.

The genus name is from Latin vexillum for flag and Greek ichthys for fish. The dorsal fin has a flag-like pattern and about thirteen alternating dark and light stripes resembling the flag of the United States.

V. atripinnis has a body long and low, flattened ventrally to anal fin and then rising to caudal peduncle. Dorsal surface forms gentle arc from snout to dorsal fin and then slowly lowering to caudal peduncle.

Head small and roughly conical. Eye large. Mouth inferior. Upper lip plicate, about half width of lower lip; lower lip plicate proximally and with cross furrows distally; lower lip with distal split between left and right lobes.

Dorsal fin roughly triangular in juveniles and females, becoming almost rectangular in nuptial males; located approximately mid body; ii,8–10 (usually 9). Anal fin rounded, broader in nuptial males; ii,6–7 (usually 6). Caudal fin emarginate with rounded lobes, i,8,8,i.

Pectoral fin short and rounded with leading unbranched rays and anterior margin of first branched ray with fleshy pad; located at ventral margin of body; ii,12,i. Pelvic fins rounded, originating below middle of dorsal fin; i,6–8 (usually 7),i.

Lateral line complete: Scales small, 46–50 in lateral line, 16–20 predorsal scale rows, 9 caudal peduncle scale rows, 16 circumpeduncular scale rows, 31–32 circumferential scales. Scales of breast and nape deeply embedded.

Vertebrae 43–45. 35 right and 39 left pharyngeal teeth; ventral most teeth with U-shaped cusps (shallowest in middle, longest edge medial) and dorsal most teeth thin and filelike; pharyngeal arch narrow, not much wider than teeth; single tooth present on neck of arch (portion of arch ventral to widened section).

Coloration: Body distinctly dark above (base color tan with overlying dark markings) and white below. Head with thick, diffuse stripe from tip of snout, through eye, to dorsal margin of opercle. Body with approximately seven black stripes running entire length separated by tan to cream interspaces.

Faint dorsal saddles present below stripes, first behind head, second below origin of dorsal fin (slanted anteroventrally), third behind dorsal fin (slanted posteroventrally), fourth at middle of caudal peduncle (wedge-shaped, narrowest dorsally), and fifth at base of caudal fin; second and fourth saddles darkest.

Dorsal fin clear to hyaline with large, black spot anterodistally on first five to six rays with spot continuing only on extreme distal portion of remaining rays. Other fins hyaline with caudal darker; caudal also with broad, dark stripe down middle and sometimes with dark edge.

Nuptial specimens darker often with a dark mark over the pectoral girdle that extends medially behind opercular opening and interradial membranes of pectoral and/or anal fins pigmented (mainly in center third of length of fin). Color in life is similar, but pectoral fins and dorsal and ventral margins of caudal fin are rust-colored with lighter yellow to rust coloring on pelvic and anal fins.

Sexual Dimorphism: Males much smaller than females with larger anal fin (anal fin height to SL ratio 21.4–33.7% vs. 7.9–17.2%) and a more rectangular dorsal fin with a greater depressed dorsal fin length to SL ratio 22.3–33.4% (vs. 20.0–22.3%). Tubercles are found in both males and females.

Tubercles in females are small and present on anal fin and caudal peduncle ventral to lateral line. Nuptial males with large tubercles on the anal and caudal fins and small tubercles on much of the body (particularly caudal peduncle head and throat). Males also with some small tubercles occasionally on ventral side of pectoral fin and dorsal side of pelvic fin. Body tubercles of males best developed on caudal peduncle.

Original research

Jonathan W. Armbruster (2024), A new genus for the Blackfin Sucker, Thoburnia atripinnis (Cypriniformes: Catostomidae). Zootaxa 5536 (2): 325–335, DOI:10.11646/zootaxa.5536.2.8

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