Hemirhamphodon byssus, new, 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 : 740-742

publication ID	https://doi.org/ 10.5281/zenodo.5352848
persistent identifier	https://treatment.plazi.org/id/038487FB-AB77-FF88-FC70-FD83FA84FAA7
treatment provided by	Tatiana
scientific name	Hemirhamphodon byssus, new
status	new

Treatment

Hemirhamphodon byssus, new View in CoL species

(Figs. 9A–E, 10A, 11A, B)

Dermogenys species undetermined – Doi et al., 2001: 16, Fig. 2 View Fig

Hemirhamphodon kuekenthali View in CoL (non-Steindachner) – Anderson & Collette, 1991 (part); Kottelat & Lim, 1995 (part); Doi et al., 2001; Jongkar & Lim, 2004

Hemirhamphodon pogonognathus View in CoL (non-Bleeker) – Roberts, 1989 (part)

Material examined. — Holotype: ZRC 54067, 1 ex., 70.5 mm SL; Sarawak: Matang Wildlife Centre, Sungai Rayu; M. Kottelat et al., 5 May 1994.

Paratypes: ZRC 37832, 6 ex., 24.7–53.0 mm SL; CMK 10861, 4 ex., 12.0– 60.4 mm SL; same locality as holotype . – ZRC 26042, 7 ex., 28.0– 58.2 mm SL; CMK 8413, 10 ex., 20.2–51.2 mm SL; Sarawak: 42 km before Lundu from Kuching, after Sungai Stinggang; M. Kottelat & P. K. L. Ng, 3 Jul.1992 . – ZRC 39361, 5 ex., 31.2–54.0 mm SL; Sarawak: Sungai Stinggang, along Bau-Lundu road; H. H. Tan et al., 6 Sep.1995 . – ZRC 37873, 15 ex., 26.8–58.5 mm SL; Sarawak: Lundu-Bau road, 27 km before Bau; M. Kottelat et al., 8 May 1994 . – ZRC 39500, 16 ex., 25.5–58.7 mm SL; Sarawak: Sungai Stom Muda , 71 km before Sematan towards Bau; H. H. Tan et al., 6 Sep.1995 . – ZRC 39376, 9 ex., 39.5–58.5 mm SL; Sarawak: Sungai Stom Muda , 71 km before Sematan towards Bau; H. H. Tan et al., 7 Sep.1995 . – ZRC 39508, 12 ex., 20.2–64.4 mm SL; Sarawak: 12 km before turnoff to Sungai Cinta Matang; H. H. Tan et al., 4 Sep.1995 . – NSMT-P 0111739 , 2 ex., 40.6–68.2 mm SL; Sarawak: Rayu basin, Sendok stream down stream (0065); A. Doi, 14 Aug.1998 . – NSMT-P 0111740 , 5 ex., 45.0– 69.3 mm SL; Sarawak: Rayu basin, Sendok stream upstream (221); A. Doi, 18 Sep.1998 . – NSMT-P 0111741 , 3 ex., 45.1–71.3 mm SL; Sarawak: Rayu basin, Buluh stream (380); A. Doi, 11 Sep.1998 . – NSMT-P 0111742 , 1 ex., 61.8 mm SL; Sarawak: Rayu basin, Ijyo stream (505); A. Doi, 11 Sep.1998 . – ZRC 39405, 20 ex., 33.4–55.0 mm SL; Sarawak: Serian , Sungai Kuhas, before Kampung Lanchang along Tebelu Tebakang turnoff; H. H. Tan et al., 5 Sep.1995 . – ZRC 41206, 6 ex., 39.5–57.3 mm SL; Sarawak: Serian , tributary of Sungei Kuhas, before Kampung Lanchang along Tebelu Tebakang turnoff; H. H. Tan et al., 19 Feb.1997 .

Non-type material: ZRC 43642, 5 ex., 35.5–57.4 mm SL; Sarawak: Lundu , Sungai Sebiris, 9 km to Sematan on Lundu-Sematan road; H. H. Tan & P. Yap, 2 Oct.1998 . – ZRC 37766, 2 ex., 49.0– 63.3 mm SL; Sarawak: Bako , Sungai Senait at goldmine; N. Sivasothi et al., 30 Jun.1994 . – ZRC 39459, 8 ex., 27.6–41.8 mm SL; Sarawak: Sungai Noren , 11 km to Bau from Serikin; H. H. Tan et al., 7 Sep.1995 . – ZRC 25927, 4 ex., 33.5–58.4 mm SL; Sarawak: Sungai Jaguh , 99 km from Kuching, after Balai Ringin; M. Kottelat & K. K. P. Lim, 2 Jul.1992 . – ZRC 39872, 8 ex., 13.6–46.5 mm SL; Sarawak: Gedong peat swamps, along Serian-Sri Aman road; H. H. Tan et al., 16 Jan.1996 . – ZRC 37893, 4 ex., 39.1–62.9 mm SL; Sarawak: blackwater ditch along Sri Aman-Sibu road, ca. 1 km south of junction with Lubok Antu road; M. Kottelat et al., 10 May 1994 . – ZRC 37864, 8 ex., 11.5–60.7 mm SL; Sarawak: Sungai Nibung , ca. 1 km north of Durin ferry on Sri Aman-Sibu road; M. Kottelat et al., 15 May 1994 .

Diagnosis. — Hemirhamphodon byssus differs from its congeners in having the following suite of characters: 1) Dorsal fin with melanophores in two sizes ( Fig. 10A View Fig ) – on both male and female examples above 30 mm SL, interradial membranes on the anterior half of the dorsal fin with large and intense melanophores throughout fin depth, appearing as thin black streaks. 2) Unique dorsal fin morphology on large males above 50 mm SL (Figs. 9A, 9C–D, 10A) – distal portions of first 6 to 7 rays elongated, free of interradial membrane, projected into filaments up to four times the depth of the dorsal fin; adpressed fin rays reaching half of caudal-fin. 3). Males with an enlarged posterior projection on the fourth anal-fin ray (Fig. 9A, 11A), with third, fourth and eighth anal-fin rays branched; females with third, fourth and eighth anal-fin rays branched ( Fig. 11B View Fig ). 4) Pelvic-fin origin anterior to dorsal-fin origin. 5) Dorsal-fin rays 13 to 14 (mode 14).

Description. — See Figs. 9A–E for general appearance and Table 1 for morphometric data.

Fig. 9. Live and preserved colouration of H. byssus : A, live male from Sematan, Sarawak, not preserved (photograph right side reversed, by Daron Tan); B, ZRC 37832, 70.5 mm SL, male holotype ; C, ZRC 37832, 47.1 mm SL, female paratype ; D, E, ZRC 43642, 57.3 mm SL, male paratype from Sematan (black and white background respectively; not to scale).

Head short (head length 27.3–29.4% SL) and body slender and long (body depth 9.0–13.1% SL; caudal peduncle depth 4.8–6.3% SL; body length 68.9–72.2% SL). Lower jaw more than half of body length (54.8–66.7% BL), about 1.4–1.7 times head length; usually straight, tip bent downwards in a few specimens; dermal flange of lower jaw on male deeper than that on female. Dorsal-fin origin anterior to anal-fin origin, posterior to pelvic-fin origin, situated nearer to caudal fin (predorsal length 70.6–75.5% SL), dorsal-fin base short (dorsal-fin base length 20.8–24.3% SL); dorsal-fin rays 13–14 (mode 14); male with first 6 to 7 dorsal-fin rays elongated into filaments, adpressed rays reaching midway of caudal fin. Caudal fin elongate, rounded, caudal-fin rays 25. Anal-fin rays 8 (last ray split to base), with short base (6.0–7.7% SL), male with distinct posterior projection on base of fourth fin ray, adpressed elongated anal-fin ray reaching up to midway of caudal fin, with branched ray on rays 3, 4 and 8, andropodium developed on ray 5 to 7, rays 5 and 7 thickened throughout ( Fig. 10A View Fig ); female with rays 3, 4 and 8 branched ( Fig. 10B View Fig ). Pelvic-fin rays 8, 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 rays 8, rounded. Precaudal vertebrae 24–25, caudal vertebrae 14–16; total vertebrae 39–40 (mode 40, n = 10). First gill arch with up to 16 gill rakers. Maximum size 71.3 mm SL.

Colouration in life. — See Fig. 9E.

Adult male – Head yellowish-brown on dorsum and sides, ventrum cream. Upper jaw brownish with corresponding portion of lower jaw with 2 blue iridescent stripes with reddish band in between; dorsal surface of exposed lower jaw iridescent blue, middle section of dermal flange on lower jaw reddish with cream sub-margin; ventrum of lower jaw flange with thin black margin from tip to region directly below upper jaw. Eye with upper half of iris pale pinkish. Operculum flushed bluish with 2 to 3 iridescent blue stripes alternating with pink on posterior half of opercle. Body with reddish dorsal stripe, dorsum pinkish and sides yellowish brown with pinkish flush, ventrum cream. Dorsal fin with first 6 to 7 rays distal one-third to half with dark brown to black pigments suffused throughout the rays and interradial membrane; rest of fin hyaline. Caudal, anal and pelvic fins with bright blue margin. Pectoral fins hyaline.

Adult female: not recorded.

Colouration in preservative. — See Fig. 9A–D.

Adult male – Head brown on dorsum and sides, ventrum cream. Upper jaw dark brown, dorsal surface of exposed lower jaw black, middle section of dermal flange on lower jaw brownish and cream, ventrum of lower jaw flange with distinct thin black margin from tip to region directly below eye. Operculum with scattering of melanophores, dark brown flush on posterior part. Body with brown dorsal stripe, dorsum dark brown and sides light brown, ventrum cream; no discernable markings on body. First 6 to 7 rays on dorsal fin with intense melanophores on interradial membrane, resulting in black streaks; distal tips of anterior half of dorsal fin extended to form black filaments, reaching up to middle of caudal fin; rest of fin hyaline. Caudal, anal, pelvic and pectoral fins hyaline.

Adult female – colouration as for male, but subdued. Anterior half of dorsal fin with black streaks, as in male. All other fins hyaline. Black streaks on anterior portion of dorsal fin present in specimens larger than or equal to 30 mm SL.

Distribution. — Hemirhamphodon byssus is known from the lowland stream systems in southern Sarawak that include Sematan, Lundu, Bau, Batu Kawa, Matang, Bako, Serian, Balai Ringin, Gedong and Sri Aman ( Fig. 7 View Fig ). From Sibu northwards (including Bintulu and Baram areas, and Brunei Darussalam), it is replaced by H. kuekenthali with which it is apparently allopatric. This distribution pattern is shared with the following allopatric species pairs (in south–north orientation): Rasbora kalochroma / R. kottelati ( Lim, 1995) , Betta ibanorum / B. akarensis (Tan & Ng, 2004, 2005).

Field notes. — Hemirhamphodon byssus occurs in streams of lowland forest and peat swamps. In streams with clear water, the body is lighter in colour; while in tannin stained waters, the body tends to be darker coloured, at times appearing black. Etymology. — From the Latin byssus , meaning fine thread, in allusion to the distinct filamentous dorsal-fin rays of large males. Used as a noun in apposition.

Comparisons with congeners. — Hemirhamphodon byssus can be distinguished from its closest congener, H. kuekenthali , by the following characters: anterior half of dorsal fin with black streaks on the interradial membrane (vs black streaks in the middle, Fig. 10B View Fig ); anterior half of dorsal fin with filamentous fin rays reaching up to middle of caudal fin (vs small extensions or none); up to 16 gill rakers on the first gill arch (vs 18). The filamentous dorsal-fin rays of H. byssus are distinct and pronounced in large male specimens from the southern parts of Sarawak (Sematan, Lundu, Bau, Batu Kawa, Matang, Rayu, Bako, Serian, Balai Ringin and Gedong). From Sri Aman northwards to region south of Sibu, the filamentous fin rays are not as pronounced; but the diagnostic black streaks on the dorsal fin are present.

Remarks. — Hemirhamphodon kuekenthali was described by Steindachner (1901) based on specimens obtained from the Baram River in northern Sarawak. It was regarded as a synonym of H. pogonognathus until it was revalidated by Anderson & Collette (1991). They designated a lectotype for H. kuekenthali and diagnosed it as the only species with two types of melanophores on the dorsal fin. As they did not have access to fresh specimens from southern Sarawak, they were not able to discern differences between the populations in the northern and southern parts of Sarawak. Subsequent workers identified halfbeaks from all over Sarawak as H. kuekenthali (e.g., Kottelat & Lim, 1995; Jongkar & Lim, 2004). Doi et al. (2001) did observe the dorsal fin extensions in only three specimens among their more than 1,600 specimens from the Rayu basin of western Sarawak but listed these as ‘ Dermogenys species undetermined’. Without access to large series of Hemirhamphodon from various parts of Sarawak for comparison, it would not have been likely for H. byssus to be recognised as distinct from H. kuekenthali .