Akysis pulvinatus, Heok Hee Ng, 2007

Heok Hee Ng, 2007, Akysis pulvinatus, a new species of catfish (Siluriformes: Akysidae) from southern Thailand., Zootaxa 1608, pp. 51-58 : 52-56

Akysis pulvinatus , sp. nov.

(Fig. 1)

Type material. Holotype: UMMZ 248249 , 29.6 mm SL; Thailand; Ranong province, stream draining into Andaman Sea upstream of Kapoe , 9°34'14.0"N 98°41'40.4"E; J. Bohlen & V. Š lechtová, 5 April 2007.

Paratypes: UMMZ 245696 , 26.5 mm SL; Thailand: Ranong province, Baan Na district, hillstreams flowing from Langkatuek, Klong Naka ; K. Udomritthiruj, July 2005. UMMZ 248250 (2), 22.8-23.9 mm SL; Thailand; Phang Nga province, Tapi River drainage, Khlong Sok at Khao Sok canoe point, ca 5 km upstream of 'fish cave' , 8º52'45.8"N 98º41'19.4"E; J. Bohlen & V. Š lechtová, 5 April 2007. ZRC 51009 (3), 21.7-26.6 mm SL; data as for holotype.

Diagnosis. Akysis pulvinatus is distinguished from congeners (except for A. brachybarbatus , A. fuliginatus , A. longifilis , A. pictus , A. prashadi and A. vespa ) in lacking serrations on the posterior edge of the pectoral spine. It is distinguished from A. brachybarbatus in having a deeper caudal peduncle (9.4-10.3% SL vs. 7.9- 8.1), narrower head (21.9-25.1% SL vs. 25.5-28.0) and the presence (vs. absence) of a yellow snout, from A. fuliginatus in having a longer adipose-fin base (23.0-25.2% SL vs. 15.1-19.5), a gently forked (vs. truncate) caudal fin, and presence (vs. absence) of light-colored markings on the head and body, and from A. longifilis in having a deeper body and caudal peduncle (depth 13.2-16.0% SL vs. 9.7-13.6 and 9.4-10.3% SL vs. 5.6- 7.2 respectively), and shorter nasal and maxillary barbels (reaching posterior margin of orbit vs. dorsalmost limit of gill opening, 13.9-57.5% HL vs. 67.4-96.4, and reaching middle of pectoral-fin base vs. vertical through middle of dorsal-fin base, 78.5-105.0% HL vs. 123.2-159.6 respectively). Akysis pulvinatus differs from A. pictus and A. prashadi in having a longer head (27.6-29.8% SL vs. 20.9-25.1) and the presence (vs. absence) of a yellow snout. It is further distinguished from A. pictus in having more rounded pale colored patches on the body (vs. with elongate pale patches that typically extend throughout the dorsal surface of the entire postdorsal distance). Akysis pulvinatus most closely resembles A. vespa in color pattern, but differs from it in having a longer adipose-fin base (23.0-25.2% SL vs. 16.2-21.6), deeper caudal peduncle (9.4- 10.3% SL vs. 7.6-9.1) and caudal fin with lower lobe longer than upper (vs. both lobes approximately equal). Some specimens of A. varius also lack serrations on the posterior edge of the pectoral spine, but A. pulvinatus is easily distinguished from it in having a gently forked (vs. truncate) caudal fin.

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 to end of caudal peduncle. Ventral profile flat to anal-fin base, then sloping gently dorsally to end of caudal peduncle. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Skin tuberculate. Lateral line incomplete, ending at vertical through pelvic-fin base. Vertebrae 14+17=31 (1).

Head depressed and broad, triangular when viewed laterally and 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. Branchiostegal rays 6 (2). Gill rakers on first arch 2+8 (1) or 2+9 (1). Bony elements of dorsal surface of head covered with thick, tuberculate skin. Eye subcutaneous, 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 just beyond posterior orbital margin. Inner mandibular-barbel origin close to midline, extending almost to vertical through base of pectoral spine. Outer mandibular barbel originates posterolateral of inner mandibular barbel, extending to middle of pectoral-fin base.

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,4,i (7) rays; fin margin convex; spine short and straight. Adipose fin with anterior margin concave and posterior margin angular. Caudal fin gently forked, with lower lobe longer than upper and i,6,6,i (7) principal rays. Procurrent rays symmetrical and extending only slightly anterior to fin base. Anal-fin base ventral to adipose-fin origin. Anal fin with convex margin and iii,6 (4), iii,6,i* (2) or iv,6 (1) rays. Pelvic-fin origin at vertical through posterior end of dorsal-fin base. Pelvic fin with slightly convex margin and i,5 (7) rays; tip of adpressed fin just reaching anal-fin origin. Pectoral fin with I,7 (3) or I,7,i* (4) rays; fin margin posteriorly convex; anterior spine margin smooth, posterior margin without serrations.

Coloration. In ethanol: dorsal surface and sides of head and body chocolate brown, with anterior and posterior nostrils rimmed with yellow. Snout with yellow extending to anterior edge of anterior nostrils. Belly, chest and ventral surfaces of head and body yellow. Dorsal half of body with two almost round, saddle-shaped yellow spots: first on sides of body between dorsal and adipose fins, second more elongate and between posterior end of adipose-fin base and caudal flexure. Ventral half of body with two similar saddle-shaped, yellow spots: first between anal and pelvic fins and second between posterior base of anal fin and caudal flexure. Posterior dorsal and ventral spots separate in some individuals, partially coalescent in others. Proximal two thirds of dorsal fin chocolate brown, remaining third hyaline with scattered chocolate brown spots. Anal and pelvic fins hyaline with very few chocolate brown spots. Proximal one-third of pectoral fin with faint brown band formed by scattered melanophores; rest of fin hyaline. Caudal fin chocolate brown with distal one-third of both upper and lower lobes with large hyaline spot. Adipose fin chocolate brown, with yellow blotches on anterior, posterior and dorsal margins. Barbels dark yellow with brown rings. Live coloration similar, but with darker yellow color in pale regions of head and body (Fig. 2).

Distribution. Known only from the upper Tapi River drainage and hillstreams flowing into the Andaman Sea on the western half of the Isthmus of Kra (Fig. 3).

Habitat. The type locality of A. pulvinatus is a stream with both slow-flowing (8 m wide) and riffle (5 m wide) areas (Fig. 4). The substrate consisted of gravel and larger rocks, with the catfish being found between the rocks, particularly in the riffle areas. The water was clear, with a temperature of 29.3°C and a pH of 8. Other fish species collected at this locality include: Homaloptera smithi , Schistura sp., S. robertsi , Hara sp. and Mastacembelus armatus .

Etymology. From the Latin noun pulvinus, meaning an elevation; in reference to the long-based adipose fin of this species.

Discussion

Akysis pulvinatus superficially resembles A. vespa very closely, but differs considerably from it in several respects, viz. the longer adipose-fin base and deeper caudal peduncle, which are evident when the two species are compared side by side (Fig. 5). Additionally, there are slight differences in the color pattern of the two species. In the A. pulvinatus examined, the yellow dorsal and ventral spots between the dorsal and adipose fins frequently do not coalesce into a distinct yellow band (there is frequently a very thin region along the lateral myoseptum that the spots do not overlap; Fig. 5) and even when they do, the outlines of the component spots are still faintly evident (in the form of a thin broken brown line in the region where the spots coalesce), while in all material of A. vespa examined, this feature assumes the form of an oblique irregular band, without clear indication that it is formed from the coalescence of two spots (Fig. 5). Since there is not enough material of A. pulvinatus to determine the full extent of color variation in this species, this difference is noted, but not used as a diagnostic character.

Akysis pulvinatus is sometimes found syntopically with Pseudobagarius leucorhynchus , another akysid catfish that shares with it a pattern of bold yellow and brown bands on the head and body. The striped pattern has been hypothesized to be a form of aposematic coloration used in Batesian mimicry in A. vespa (model) and Caelatoglanis zonatus (mimic) by Ng & Kottelat (2005). In this case, both A. pulvinatus and P. leucorhynchus , like other akysids (de Pinna, 1996), possess a venom apparatus associated with the dorsal- and pectoralfin spines. The possibility exists that the bold, striped coloration of the two catfish serves as aposematic coloration used in Müllerian mimicry. However, this hypothesis awaits further testing in the absence of field data.

Akysis pulvinatus is known from the western half of the Isthmus of Kra, an area where the freshwater fish fauna is not well known. The freshwater fish fauna of this region is traditionally thought to be identical to that of the rest of the Malay Peninsula (Kottelat, 1989). Recent collections from this region (the western half of which includes the southern tip of the Tenasserim range) have suggested otherwise, also yielding an undescribed species of Hara (currently being described in another study; Ng & Kottelat, 2007). Considerable endemism may exist in this region and more comprehensive surveys are needed.