Traccatichthys tuberculum, Du & Chan, 2012

Du, Chun-Xian & Chan, Bosco Pui Lok, 2012, Traccatichthys tuberculum, a new species of nemacheiline loach from Guangdong Province, South China (Pisces: Balitoridae), Zootaxa 3586, pp. 304-312 : 305-308

Traccatichthys tuberculum , new species, Du, Zhang & Chan

( Fig. 1a)

Holotype. IHB 201105029 , 87.7 mm SL; China: Guangdong Province: Jian-Jiang, a coastal river flowing into South China Sea , Xinyi County; collected by Z.W. Sun and Z.G. Jiang, May, 2011.

Paratypes. IHB 201105004 , 201105007–18 , 201105020 , 201105022–8 , 201105030 , 22 specimens, 54.5–75.1 mm SL, same data as holotype .

Diagnosis. Traccatichthys tuberculum differs from other Chinese species ( T. pulcher and T. zispi ) in having a wider interorbital space (width 39.1–48.4% HL vs. 27.4–33.7 in T. zispi and 27.2–35.4 in T. pulcher ), a longer caudal peduncle (length 14.6–19.9% SL vs. 11.9–15.4 and 12.6–14.1; Fig. 2a), and longer pectoral fins (length 16.1–22.2% SL vs. 13.2–17.9 and 11.9–17.6; Fig. 2b). Traccatichthys tuberculum is similar to T. zispi (Fig. lb) in the shared absence of a black band along the leading dorsal-fin rays, subdistal and median black bands across the dorsal fin, and submarginal black streaks on the caudal-fin lobes that are characteristic of T. pulcher ( Fig. 1c), but differs from T. zipsi in having a more anteriorly (vs. posteriorly) positioned anal fin (preanal length 72.0–76.5% SL (vs. 77.6–81.7). Traccatichthys tuberculum , is distinct from the Vietnamese species, T. taeniatus , in having a roughly round (vs. vertically elongated) black bar on the caudal-fin base, and in lacking a black band along the posterior part of the distal margin of the anal fin.

Description. Morphometric data for type specimens are given in Table 1. Body long, slightly spindle-shaped, anteriorly subcylindrical and posteriorly compressed laterally. Body densely scaled except for head. Dorsal profile of head slightly convex, predorsal profile of body straight. Dorsal-fin base and postdorsal profile somewhat concave. Ventral profile of head straight, of body from pectoral-fin insertion to anal-fin origin slightly convex; anal-fin base straight, postanal profile slightly concave. Greatest body depth anterior to dorsal-fin origin, least caudal-peduncle depth nearer to caudal-fin base than to posterior end of anal-fin base. Caudal peduncle stout, deeper than long.

Head slightly compressed laterally, width less than height, and roughly triangular in lateral view. Snout protruding, obtuse in dorsal view, longer than postorbital length of head; eye moderately large, close to dorsal profile of head; interorbital space convex, width shorter than snout length, and approximately 1.5 times eye diameter. Nostrils closer to anterior margin of eye than to snout tip; anterior and posterior nostrils closely positioned; anterior one pierced at extremity of short tube; posterior one oval, slightly larger than anterior one.

Mouth inferior and transversely arched, with narrow opening. Lips thick, papillose; upper lip without median incision, covered with papillae arranged finely and regularly in two rows with large papillae of anterior row larger than those of posterior row; lower lip medially covered with many large papillae. Jaws covered by lips; upper jaw with well-developed processus dentiformis; lower jaw spoon-shaped, without median incision. Three pairs of barbels, two rostral pairs and one maxillary pair; inner rostral pair extending to corner of mouth, outer rostral pair reaching vertical through posterior nostril; maxillary barbel reaching vertical through posterior margin of eye. Lateral line complete, reaching caudal-fin base.

Dorsal fin with three simple and 12 branched rays; origin nearer to snout tip than to base of caudal fin; dorsalfin base longer than its last simple ray. Pectoral fin with one simple and 12 branched rays; inserted immediately anterior to vertical through posteriormost point of operculum; tip of adpressed fin extending beyond midway to pelvic-fin insertion, almost to or slightly beyond a vertical line through dorsal-fin origin. Pelvic fin with one simple and seven branched rays, inserted posterior to vertical through dorsal-fin origin; tip of adpressed fin not extending to anal-fin origin. Anal fin with three simple and five branched rays; distal margin straight or slightly convex; origin closer to caudal-fin base than to pelvic-fin insertion; tip of adpressed fin, almost extending to caudal-fin base. Caudal fin with 7–8+8 = 15–16 branched rays; emarginate, upper and lower lobes equal in length.

Intestine short and straight, without zigzag loop behind posterior portion of U -shaped stomach. Gas bladder bipartite; anterior chamber invisible, entirely enclosed in capsule; posterior chamber long and oval.

Coloration in preservative. Top and sides of head black brown; ground color of back and upper half of flank above lateral line yellowish brown, and lower half below lateral line and abdomen white or grey. No spots or stripes on head. Back and sides of body with many irregular cross-shaped brownish blotches, especially in predorsal region; 15–16 herring-bone lines or chevrons fused to form longitudinal black stripe starting from above pectoral fin, extending along lateral line and terminating anterior to caudal-fin base; stripe darkest from above pectoral fin to anal-fin origin, with indented upper and lower margins. Black spot medially on caudal-fin base. Dorsal fin crossed by subdistal and median dusky bands; simple rays black with hyaline distal edge. Caudal fin with longitudinal dark stripe on median rays and submarginal dark stripe along each lobe; distal margin dark.

Sexual dimorphism. Many breeding tubercles on each interradial membrane of pectoral fin in males, missing in females. Genital papilla larger in females, inconspicuous in males.

Distribution. Known only from the Jian-Jiang, a coastal river in Guangdong Province, South China ( Fig. 3).

Etymology. The specific epithet is from the Latin word tuberculum , referring to the presence of tubercles on the dorsal surface of the pectoral-fin rays; treated as a noun in apposition.