Akysis longifilis, Heok Hee Ng, 2006

Heok Hee Ng, 2006, Akysis longifilis, a new species of catfish (Teleostei: Akysidae) from Myanmar., Zootaxa 1150, pp. 19-30 : 20-25

Akysis longifilis sp. nov.

(Fig. 1)

Type material. Holotype: UMMZ 246172, 33.8 mm SL; Myanmar: Bago division, Pyu township, Pyu stream (tributary of Sittang River) ca. 229 km from Yangon, 18°29’N 96°26’E; Than Kyaw Toe, September 2005.

Paratypes: UMMZ 245966 (7), 31.5-53.1 mm SL ; UF 161587 (2), 33.7-34.0 mm SL; data as for holotype .

Non-type material. UMMZ 246204 (1 c&s), 52.7 mm SL; data as for holotype.

Diagnosis

Akysis longifilis is a member of the A. variegatus species group and can be distinguished from congeners in the group (except for A. brachybarbatus , A. fuliginatus , A. pictus , A. prashadi , A. variegatus , A. varius and A. vespa ) in having a smooth (vs. serrated) posterior edge of the pectoral spine. It differs from A. brachybarbatus in having a narrower head (21.1-24.7% SL vs. 25.5-28.0) and a more slender caudal peduncle (5.6- 7.2% SL vs. 7.9-8.1), and from A. fuliginatus in having a longer adipose-fin base (25.7- 31.1% SL vs. 15.1-19.5), more slender body (9.7-13.6% SL vs. 14.1-16.6) and caudal peduncle (5.6-7.2% SL vs. 10.1-10.5), longer nasal and maxillary barbels (nasal barbel length 67.4-96.4% HL vs. 52.1-58.2; maxillary barbel length 123.2-159.6% HL vs. 100.0-109.1), presence of light saddle-shaped spots on the body (vs. uniformly dark body), and a forked (vs. truncate) caudal fin. Akysis longifilis can be distinguished from A. pictus in having a more slender caudal peduncle (5.6-7.2% SL vs. 7.7-8.5), longer adipose-fin base (25.7-31.1% SL vs. 22.0-23.6), and longer nasal and maxillary barbels (nasal barbel length 67.4-96.4% HL vs. 54.3-56.7; maxillary barbel length 123.2-159.6% HL vs. 95.7-128.8), and from A. prashadi in having a longer caudal peduncle (18.3- 23.2% SL vs. 16.5-18.4). It differs from A. variegatus in having longer nasal and maxillary barbels (nasal barbel length 67.4-96.4% HL vs. 33.3-62.3; maxillary barbel length 123.2-159.6% HL vs. 78.3-114.8), from A. varius in having a forked (vs. truncate) caudal fin, and from A. vespa in having a longer adipose-fin base (25.7-31.1% SL vs. 17.6-21.1), more slender caudal peduncle (5.6-7.2% SL vs. 7.6-8.5), longer nasal and maxillary barbels (nasal barbel length 67.4-96.4% HL vs. 54.5-72.5; maxillary barbel length 123.2-159.6% HL vs. 89.0-98.2), and more vertebrae (33-35 vs. 31-32).

Description

Biometric data in Table 1. Body moderately compressed. Dorsal profile rising evenly but not steeply from tip of snout to origin of dorsal fin, then sloping gently ventrally from there to end of caudal peduncle. Ventral profile flat to anal-fin base, then sloping gently dorsally from there to end of caudal peduncle. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Skin tuberculate. Lateral line complete and midlateral. Vertebrae 17+16=33* (2), 16+18=34 (2), 17+17=34 (2), 18+16=34 (1) or 17+18=35 (3).

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 one-third of distance from ventral midline of body to base of pectoral spine. 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 vertical through middle of dorsal-fin base. Nasal barbel slender, extending to dorsalmost limit of gill opening. Inner mandibular-barbel origin close to midline, extending to base of pectoral spine. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending beyond base of last pectoral-fin ray.

Mouth subterminal, premaxillary tooth band not exposed when mouth is closed. Oral teeth small and villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rounded, 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,3,ii (1), I,4,i* (8) or I,5 (1) rays; fin margin convex; spine short and straight. Adipose fin with anterior margin slightly concave and posterior margin angular, origin at vertical through middle of pelvic-fin base. Caudal fin gently forked, with i,6,6,i (10) principal rays; lower lobe slightly longer and broader than upper lobe. Procurrent rays symmetrical and extending only 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* (7) or iii,6 (3) rays. Pelvic-fin origin at vertical through posterior end of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (10) rays; tip of adpressed fin not reaching anal-fin origin. Pectoral fin with I,6,i (10) rays; fin margin posteriorly convex; anterior spine margin smooth, posterior margin without serrations.

Coloration. In ethanol: dorsal surface and sides of head medium grayish brown, with few darker brown spots randomly scattered throughout. Dorsal surface and sides of body dark grayish brown. Belly, chest and ventral surfaces of head and body light brown. Dorsal half of body with two elongate saddle-shaped light brown spots: first on body at anterior three-quarters of adipose-fin base, second more elongate and between posterior fifth of adipose-fin base and caudal flexure. Ventral half of body with two similar saddle-shaped, light brown spots: first between anal and pelvic fins and second between posterior base of anal fin and caudal flexure. Anterior ventral spot largely coalescent with light brown coloration of ventral surfaces. Proximal two thirds of dorsal fin chocolate brown. Anal and pelvic fins hyaline with very few brown spots forming indistinct transverse band through middle of fin. Proximal half of pectoral fin with reticulate brown band; rest of fin hyaline. Caudal fin chocolate brown with distal one third of both upper and lower lobes with large, mostly hyaline spot (with scattered melanophores). Adipose fin dark grayish brown, except where lighter brown saddles-shaped spots on body run through fin. Barbels light brown, maxillary pair sometimes with few brown rings proximally.

Etymology

From the Latin longus, meaning long, and filum, meaning thread, in reference to the long barbels of this species. Used as a noun.

Distribution

Known from the type locality in the Sittang River drainage, southern Myanmar (Fig. 2).

Discussion

Three other species of Akysis are recorded from Myanmar (Ng & Kottelat, 2004): A. pictus , A. prashadi and A. vespa . These species are not known to occur sympatrically with A. longifilis (which is known from the Sittang River drainage; A. pictus and A. vespa are known from the Ataran River drainage, and A. prashadi from the Irrawaddy River drainage). Akysis longifilis differs from all three species by the differences outlined in the diagnosis, and these differences are not solely due to ontogeny. Biplots of the relevant diagnostic biometric characters for the four species (Figs. 3-7) show that the regression lines are significantly different (ANCOVA, P<0.01 in all cases).

Both A. pictus and A. vespa are also found in southern Myanmar, but differ considerably from A. longifilis in coloration. Akysis longifilis possesses two distinct light saddle-shaped spots on the upper surfaces of the postdorsal region, while A. pictus possesses a very long light saddle-shaped spot in the same region (Fig. 8). The color pattern in A. pictus is unique to this species and reminiscent of that seen in species of Acrochordonichthys . Akysis vespa possesses two distinct vertical light bands (instead of saddle-shaped spots) in the postdorsal region.

Of the biometric characters, only barbel lengths distinguish A. longifilis from A. variegatus . However, there are also noticeable differences in the color patterns of the two species. Although all of the specimens of A. variegatus I examined have the color pattern strongly faded or missing, both Bleeker (1862: Pl. 83 Fig. 1) and Weber & de Beaufort (1913: Fig. 150) show this species to possess a distinct light colored vertical band on the caudal peduncle. The caudal peduncle of A. longifilis , in contrast, is marked by two light colored saddle-shaped spots (one dorsal and one ventral), which do not coalesce into a vertical band. Furthermore, the two species have widely separate distributions ( A. longifilis in the Sittang River drainage and A. variegatus in Java), with the two areas having significantly different fish faunas (Kottelat, 1989; Rainboth, 1991).