Hemirhamphodon kecil, Tan & Lim, 2013

Tan, Heok Hui & Lim, Kelvin K. P., 2013, Three New Species Of Freshwater Halfbeaks (Teleostei: Zenarchopteridae: Hemirhamphodon) From Borneo, Raffles Bulletin of Zoology 61 (2), pp. 735-747 : 742-744

Hemirhamphodon kecil , new species

( Figs. 12A–E , 13A, B )

Hemirhamphodon pogonognathus (non-Bleeker) – Anderson & Collette, 1991 (part); Christenson, 1992; Kottelat et al., 1993 (part); Kottelat, 1994.

Material examined. — Holotype: MZB 17211, 37.4 mm SL; Kalimantan Timur: Mahakam basin; downstream of Taman Wisata Air Terjun at Tanah Merah; H. H. Tan & D. Wowor, 2 Dec.1999 . Paratypes: MZB 17212, 3 ex., 30.4–33.4 mm SL ; ZRC 45684, 30 ex., 17.0– 40.8 mm SL; same locality as holotype . — MZB 6002 , 20 ex., 20.4–44.7 mm SL; CMK 21765, 19 ex., 19.4–46.0 mm SL; Kalimantan Timur: Mahakam drainage, Belayan system, REA plantations, Sungai Nyiur, PT SYB (Sasany Yudha Bhakti) Tepian Estate , 0°10'45"N 116°16'04"E ; R. K. Hadiaty & M. Kottelat, 19 Nov.2009 . — MZB 6003 , 8 ex., 28.0–40.0 mm SL; CMK 21871, 8 ex., 32.2–40.6 mm SL; Kalimantan Timur: Mahakam drainage, Belayan system, REA plantations, Long (=Sungai) Buluh , Damai estate, 0°14'29"N 116°19'14"E ; R. K. Hadiaty & M. Kottelat, 22 Nov.2009 .

Diagnosis. — Hemirhamphodon kecil differs from its congeners in having the following suite of characters: 1) Absence of discernable markings on body and fins, except dorsal part of caudal fin base with sparse black pigments on both male and female; and submargin of dorsal fin suffused with black pigments ( Fig. 12D, E ). 2) Small adult size, up to 41 mm SL (only H. tengah is smaller). 3) Adult sizes for male and female similar (as with H. tengah ), other congeners with males up to 50% larger than females. 4) Males with an enlarged posterior projection on the fourth anal-fin ray ( Fig. 13A ), with third, fourth, sixth and eighth anal-fin rays branched; females with third, fourth and eighth anal-fin rays branched ( Fig. 13B ). 5) Pelvic-fin origin anterior to dorsal-fin origin. 6) Dorsal-fin rays 14 to 15 (mode 14).

Description. — See Fig. 12A–E for general appearance and Table 1 for morphometric data.

Head short (head length 25.1–28.1% SL) and body slender and long (body depth 9.3–11.1% SL; caudal peduncle depth 4.4–5.8% SL; body length 71.4–74.9% SL). Lower jaw about half of body length (44.0–59.9% BL), about 1.2–1.6 times head length; usually straight, tip bent downwards in a few specimens; dermal flange of lower jaw on male deeper than on female. Dorsal-fin origin anterior to anal-fin origin, posterior to pelvic-fin origin, situated nearer to caudal fin (predorsal length 70.6–74.9% SL), dorsal-fin base short (dorsal-fin base length 21.5–24.9% SL); dorsal-fin rays 14–15 (mode 14); male without dorsal-fin ray extensions; dorsal fin of male about twice deeper than that of female. Caudal fin elongate, rounded, caudal-fin rays 25. Anal-fin rays 8 (last ray split to base), with short base (6.4–8.4% SL), male with distinct

E

posterior projection on base of fourth fin ray, adpressed elongated anal-fin ray reaching caudal-fin base, with branched ray on rays 3, 4, 6 and 8, andropodium developed on ray 5 to 7, rays 5 and 7 thickened throughout ( Fig. 13A ); female with anal rays 3, 4 and 8 branched ( Fig. 13B ). Pelvic-fin with 6 rays, fins adpressed to body, male with longer inner rays, adpressed rays reaching anal-fin origin; female with shorter rays, adpressed rays not reaching anus. Pectoral-fin rounded, with 9 rays. Precaudal vertebrae 24–25, caudal vertebrae 14–16; total vertebrae 39–41 (mode 39, n = 10). First gill arch with up to 16 gill rakers. Maximum size 41 mm SL.

Colouration in preservative. — See Figs. 12A–E .

Adult male – Head brown on dorsum, sides and ventrum cream. Upper rim of lower jaw below upper jaw with black stripe, ventrum of dermal flange on lower jaw with distinct black margin from tip to region directly below eye. Operculum with scattering of melanophores, appearing dusky on posterior part. Body with brown dorsal stripe, dorsum brownish and sides cream with diffused pale brown longitudinal stripe, ventrum cream. Dorsal fin with submargin suffused with black pigments. Dorsal region of anterior part of caudal-fin base with sparse black pigments. Rest of fins hyaline.

Adult female – colouration as for male. All fins hyaline.

Distribution. — Hemirhamphodon kecil is currently known only from East Kalimantan, Indonesian Borneo, in the waterways of the lower Mahakam basin that drain eastwards into the Makassar Strait ( Fig. 7 ).

Field notes. — Hemirhamphodon kecil occurs in streams with submerged bank vegetation and clear water of pH 7.0 flowing over rocky, sand and silt substratum. It tends to school in small groups of about 3 to 5 individuals at the surface, preferring quiet pools and dwelling near or under overhanging bank vegetation. Syntopic ichthyofauna consists of Osteochilus vittatus , Rasbora elegans , Systomus binotatus (Cyprinidae) , Betta patoti , Trichopodus trichopterus (Osphronemidae) , and Channa lucius (Channidae) .

Etymology. — From the Bahasa Indonesian word ‘kecil’, meaning small, in reference to the diminutive size of this species. Used as a noun in apposition.

Comparisons with congeners. — Hemirhamphodon kecil can be distinguished from its closest congener, H. pogonognathus , by the following characters: smaller adult size (41 vs. 58 mm SL); longer body (71.4–74.9 vs 68.7–71.8% SL); shorter head (25.1–28.1 vs 28.4–30.5 mm SL); shorter dorsal-fin base (21.5–24.9 vs 24.0–26.5% SL).

Figures

Fig. 12. Preserved colouration of H. kecil: A, ZRC 54684, 37.4 mm SL, male paratype; B. MZB 17211, 34.6 mm SL, male holotype; C, ZRC 54684, 38.6 mm SL, female paratype; D, ZRC 54684, 37.4 mm SL male paratype (white background); E, ZRC 54684, 38.6 mm SL, female paratype (white background; not to scale).

Fig. 13. Radiographs of anal fin of H. kecil: A, MZB 17211, 37.4 mm SL male holotype; B, ZRC 54684, 38.6 mm SL female paratype.

Fig. 7. Distribution of H. sesamum (solid circle), H. byssus (solid square) and H. kecil (hollow circle) in Borneo.