Akysis bilustris, Ng, Heok Hee, 2011

Ng, Heok Hee, 2011, Akysis bilustris, a new species of catfish from southern Laos (Siluriformes: Akysidae), Zootaxa 3066, pp. 61-68 : 62-63

Akysis bilustris sp. nov.

( Fig. 1 )

Akysis ephippifer (non Ng & Kottelat)—Kottelat, 2001: 138, Fig. 390

Type material. Holotype: ZRC 53111, 25.3 mm SL; Laos: Attapeu Province, Xe Kong where Houai Tamopat enters it, downstream of Ban Khanmaknao, 14°36'31"N 106°33'8"E; M. Kottelat et al., 22 May 2009.

Paratypes: CMK 21247 (1), 25.6 mm SL; Laos: Attapeu Province, Xe Pian, about 2 km upstream of Ban Mai, 14°43'31"N 106°29'42"E; M. Kottelat et al., 20 May 2009. CMK 15692 (1), 22.9 mm SL; Laos: Attapeu Province, Xe Pian at Ban Mai, 14°42'22"N 106°29'46"E; M. Kottelat et al., 22 May 1999. CMK 21457 (1), 27.2 mm SL; Laos: Attapeu Province, Xe Kong, riffles in gravel banks at Ban Khanmaknao, 14°36'46"N 106°33'13"E; M. Kottelat et al., 22 May 2009. CMK 21411 (2), 23.1–26.1 mm SL; ZRC 53112 (2), 23.5–24.5 mm SL; data as for holotype.

Diagnosis. Akysis bilustris is distinguished from congeners by a combination of the following characters: eye diameter 14.0–17.5% HL; serrae on posterior margin of pectoral spine 2–3 and longer than half width of spine, pectoral fin reaching to or overlapping pelvic-fin base (length 24.5–29.3% SL), adipose-fin base length 14.3–18.3% SL, body depth at anus 11.4–13.8% SL, caudal-peduncle length 19.6–23.4% SL; caudal-peduncle depth 6.7–9.2% SL; caudal fin emarginate, and vertebrae 30–31.

Description. Morphometric data in Table 1 . Body moderately compressed. Dorsal profile gently convex from tip of snout to origin of dorsal fin, sloping gently ventrally to end of caudal peduncle. Ventral profile flat to anal-fin base, sloping gently dorsally to end of caudal peduncle. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Skin tuberculate. Vertebrae 14+16=30 (2) or 14+17=31* (4).

Head depressed and broad, with rounded snout margin when viewed from above. Anterior nostril tubular, base of nostril not in contact with base of nasal barbel. Gill openings narrow, extending from immediately ventral to posttemporal to point immediately lateral to ventral midline of body. Bony elements of dorsal surface of head covered with thick, tuberculate skin. Eye ovoid, horizontal axis longest; located entirely in dorsal half of head.

Barbels in four pairs. Maxillary barbel long and slender, extending to middle of pectoral-fin base. Nasal barbel slender, extending to base of pectoral spine. Inner mandibular-barbel origin close to midline, extending to base of pectoral spine. Outer mandibular barbel originating posterolaterally of inner mandibular barbel, extending to middle of pectoral-fin base.

Mouth subterminal, premaxillary tooth band not exposed when mouth closed. Oral teeth small and villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band gently arced, of equal width throughout. Dentary tooth band much narrower than premaxillary tooth band at symphysis, tapering laterally.

Dorsal fin located above anterior third of body, with i,4,i (6) rays; fin margin convex; spine short, straight. Adipose fin with anterior margin slightly concave, posterior margin angular; origin at vertical through middle of pelvic-fin base. Caudal fin weakly emarginate, with i,6,6,i (6) principal rays. Procurrent rays symmetrical, extending slightly anterior to fin base. Anal-fin origin at vertical through approximately midpoint of adipose-fin base. Anal fin with convex margin and iii,5,i (1), iii,6,i* (1), iv,4,i (1), iv,5,i (1), iv,6,i (1) or v,5,i (1) rays. Pelvic-fin origin at vertical through posterior end of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (6) rays; tip of adpressed fin not reaching anal-fin origin. Pectoral fin with I,5,i (6) rays; fin margin posteriorly convex; anterior spine margin smooth, posterior margin with 2–3 large serrations; serrations more than half width of spine.

Coloration. In ethanol: dorsal surface and sides of head and predorsal region roughly corresponding to area defined by neurocranium chestnut-brown, with irregular darker chocolate-brown spots randomly distributed. Dorsal surface and sides of body at and posterior to dorsal fin dark chocolate-brown. Belly, chest and ventral surfaces of head and body light brown. Dorsal half of body with two chestnut-brown saddle-shaped patches: first on body covering posterior half of interdorsal region and anterior third of adipose-fin base, second between adipose-fin base and caudal flexure. Tubercles within paler saddle-shaped markings highlighted in dark yellow. Ventral half of body with two similar but smaller pale saddle-shaped patches: first between anal and pelvic fins and second between posterior base of anal fin and caudal flexure. Dorsal-fin membrane chocolate-brown, with coloration more diffuse on distal third. Anal and pelvic fins hyaline with brown spots forming indistinct transverse bands through middle of fins; 2–3 such bands visible on pelvic fin and 3–4 such bands visible on anal fin. Pectoral fin with brown spots on fin rays forming 4–5 irregular bands. Caudal fin with reticulate chocolate-brown pattern on most of fin and proximal one third of both upper and lower lobes mostly hyaline with scattered melanophores; very thin hyaline margin on distal margin of fin. Adipose fin dark chocolate-brown, except where yellow saddles-shaped patches on body run through fin. Barbels yellow, annulated with brown rings.

Distribution. Known only from two geographically proximate localities in the Xe Kong drainage, a major subdrainage of the Mekong River in southern Laos ( Fig. 2 ).

Etymology. The specific epithet is the Latin adjective bilustris , meaning “that lasts two lustra (i.e. ten years),” in reference to the fact that the specimens comprising the type series were collected in two expeditions exactly ten years apart.

Figures

FIGURE 1. Akysis bilustris, ZRC 53111, holotype, 25.3 mm SL; Laos: Xe Kong River.

FIGURE 2. Map of the middle and lower Mekong with collection localities of A. bilustris; the symbol represents more than one locality.

Tables

TABLE 1. Morphometric data for Akysis bilustris (n = 6).

	Holotype ZRC 53111	Range	Mean±SD
%SL
Predorsal length Preanal length	36.0 61.3	33.8–39.3 57.9–68.0	36.1±1.91 61.5±3.84
Prepelvic length Prepectoral length Dorsal-fin base length Dorsal-spine length	45.1 22.5 17.8 18.2	44.5–48.0 19.5–24.3 16.0–19.2 14.3–19.2	45.9±1.42 22.2±1.66 17.4±1.06 17.1±1.85
Anal-fin base length Pelvic-fin length	19.8 13.4	15.7–24.9 13.0–14.9	19.4±3.23 13.8±0.71
Pectoral-fin length Pectoral-spine length Caudal-fin length Adipose-fin base length	29.2 20.9 30.0 15.0	24.5–29.3 19.5–24.5 26.1–30.6 14.3–18.3	27.3±1.91 21.5±2.27 28.5±1.75 15.5±1.53
Dorsal-to-adipose distance Post-adipose distance	18.2 19.0	18.0–22.6 17.7–20.7	20.1±1.97 19.3±1.04
Caudal-peduncle length Caudal-peduncle depth Body depth at anus Head length	22.1 6.7 11.9 26.5	19.6–23.4 6.7–9.2 11.4–13.8 24.3–26.5	21.4±1.34 8.3±0.85 12.1±0.89 25.2±0.90
Head width Head depth	25.7 17.0	24.7–26.9 15.2–17.9	25.6±0.78 16.4±1.03
%HL
Snout length Interorbital distance Eye diameter Nasal-barbel length Maxillary-barbel length	35.8 40.3 14.9 98.5 100.0	35.8–43.1 39.1–44.8 14.0–17.5 54.7–98.5 100.0–128.1	38.8±2.59 42.0±2.12 15.5±1.15 76.8±15.47 115.6±11.08
Inner mandibular-barbel length Outer mandibular-barbel length	49.3 71.6	49.3–84.2 71.6–106.3	65.4±12.18 93.2±13.88