Trigonostigma heteromorpha ( Duncker, 1904 )

Hui, Tan Heok, 2020, Trigonostigma truncata, a new species of harlequin rasbora from Malay Peninsula (Teleostei: Danionidae), Raffles Bulletin of Zoology 68, pp. 421-433 : 427-431

Trigonostigma heteromorpha ( Duncker, 1904)

( Figs. 1 , 4B , 5 , 7 )

Rasbora heteromorpha Duncker, 1904: 182 , pl. 1, fig. 5; Weber & de Beaufort, 1916: 79; Tweedie, 1936: 21; Herre & Myers, 1937: 55; Fowler, 1938: 57; Brittan, 1954a: 152; 1954b: 187, fig. 44; Menon, 1954: 8; Alfred, 1963: 166; 1966: 19; Mohsin & Ambak, 1983: 50 (part); Zakaria-Ismail, 1987: 406; Lim & Ng, 1990: 32; Ng & Lim, 1992: 259, table 3; 1996: 111; 1997: 249; Kottelat et al., 1993: 63, pl. 1; Tan & Tan, 1994: 353; Ng & Tan, 1997: 84; Sim, 2002: 50; Rachmatika et al., 2006: 64; Rüber et al., 2007: figs. 1–3; Collins et al., 2012 (not all molecular phylogenetic studies are included in this synonymy list, as most of them do not include locality data; and many also suffer from using the same set of sequence data without verification of vouchers, thus perpetuating errors [pers. obs.]).

Trigonostigma heteromorpha ( Duncker, 1904) : Kottelat & Witte, 1999: 54; Ng & Tan, 1999: 352, table 1; Conway, 2005: table 1, fig. 11; Tan & Kottelat, 2009: 52; Baker & Lim, 2012: 36; Kottelat, 2013: 170 (part); Chow et al., 2014: 56; Fahmi-Ahmad et al., 2015: 34, table 1; Azmai et al., 2020: 74.

Material examined. — ZRC 39918, 2 ex., 19.3–24.2 mm SL; Malaysia: Perak, Sungei Beriang, 21 km milestone from Taiping to Segama ; Tan HH et al., 18 November 1995 . — ZRC 14383, 1 ex., 28.0 mm SL; Malaysia: Selangor, Sungei Buloh forest reserve, swampy forest stream; Ng PKL & Lim KKP, 6 March 1991 . — ZRC 13794 sa, 7 ex., 9.8–25.9 mm SL; Malaysia: Johor, Panti forest stream; Ng PKL, 31 August 1990 . — ZRC 4903–4914 , 11 ex., 15.6–25.0 mm SL; Malaysia: Johor, Mawai, Sunegi Mupor; Alfred ER, 21 February 1971 . — ZRC 55562, 9 ex., 19.0– 27.6 mm SL; Singapore: Central Catchment Nature Reserve , channel between Upper Peirce and MacRitchie Reservoirs; Tan HH et al., 18 September 2007 (only the largest specimens were used for meristic counts and morphometric measurements; n=20, SL= 21.6–27.6 mm).

The following material was also examined but no measurements or counts taken — BMNH 1905.5.6 : 2–3 (2 paralectotypes), 22.3–23.2 mm SL; Malaysia : Selangor, Kuala Lumpur; Robinson HC, 1905. PENINSULAR MALAYSIA — ZRC 27602, 1 ex., 18.0 mm SL; Malaysia: Selangor, Sabak Bernam, Sungei Bernam ; Ng PKL et al., 19 September 1992 . — ZRC 13547, 2 ex., 27.9–28.3 mm SL; Malaysia: Johor, Pontian , stream adjacent to Gunung Pulai reservoir I; Ng PKL & Yeong R, 9 September 1988 . — ZRC 21243, 4 ex., 17.9–22.9 mm SL: Malaysia: Johor, Sungei Selangi , 15 km Kota Tinggi-Tanjung Sedili Road; Ng PKL et al., 22 April 1992 . SINGAPORE — ZRC 2314 (6 paralectotypes); Singapore: Botanical Garden pond . — ZRC 12405, 4 ex., 18.4–21.0 mm SL: Singapore: Sime Road forest ; Ng PKL & Lim KKP, 27 October 1989 . — ZRC 34601, 18 ex., 9.0– 18.9 mm SL; Singapore: Sime Road forest ; Lim KKP et al., May 1992 . — ZRC 34623, 2 ex., 23.0– 24.1 mm SL; Singapore Rifle Range road stream; Chang CY et al., 27 May 1993 . — ZRC 12386, 4 ex., 17.9–27.0 mm SL; Singapore Nee Soon swamp forest, second track; Lim KKP & Ng PKL, 14 April 1990 . — ZRC 38248, 7 ex., 17.0– 28.5 mm SL; Singapore Nee Soon swamp forest; Lim KKP, 20 June 1994 . INDONESIA: Riau Archipelago — ZRC 14044, 8 ex., 19.6–30.3 mm SL: Indonesia: Pulau Batam , north-western part; Ng PKL & Lim KKP, 25 February 1991 . — ZRC 33215, 5 ex., 10.0–28.0 mm SL; Indonesia: Pulau Bintan North ; Tan THT et al., 11 May 1993 . — ZRC 31540, 10 ex., 19.1–31.2 mm SL; Indonesia : Pulau Lingga, Daik; Searby M, November 1996 . INDONESIA: Sumatra — ZRC 41950, 8 ex., 11.3–25.1 mm SL; Indonesia: Sumatra: Riau, upper Indragiri ; Tan HH et al., November 1996 . — Others : ZRC 61239, 1 ex., 27.8 mm SL; obtained from aquarium trade, September 2015 .

Diagnosis. Trigonostigma heteromorpha shares with T. truncata , new species, a large black axine starting from approximately mid-body with dorsal apex near dorsal-fin origin, ventral apex near pelvic-fin origin, and caudal apex near caudal-fin base; this axine being the largest amongst all congeners. Trigonostigma heteromorpha differs from all congeners in the following combination of characters: a steep sloping lateral head to pre-dorsal region (shared with T. espei , vs. a gentle sloping lateral profile from posterior of head to predorsal region for T. truncata , T. hengeli , and T. somphongsi ); terminal mouth (shared with all except T. truncata with a sub-superior mouth); caudal apex of axine reaching caudal-fin base (shared with all except T. truncata with caudal apex not reaching); dorsal and ventral apices of axine originate near to both dorsal-fin and pelvic-fin origins (shared with T. truncata , vs. dorsal apex starting up to three scale-width posterior to dorsal-fin origin and ventral apex starting two scale-width after pelvic-fin origin in T. espei and T. hengeli ; axine reduced to thick black stripe in T. somphongsi ); dorsal fin with distinct orange/red pigments (shared with T. truncata and T. espei , vs. both T. hengeli and T. somphongsi with almost hyaline dorsal fin); and the largest adult size (up to 35 mm SL).

Description. See Figs. 1 , 4B , 7 for general appearance. See Table 2 for meristic and morphometric data. Head pointed, with terminal mouth, barbels absent. Profile of head and anterior of body with a steep slope upwards to dorsal-fin origin, presence of distinct notch between occiput and nape. Orbit relatively large (orbital diameter 35.6–44.8% HL). Body compressed, deepest at dorsal-fin origin (body depth 32.6–38.2% SL) and shallowest at caudal peduncle (caudal peduncle depth 12.6–15.8% SL). Dorsal and pelvic fins situated mid-body (predorsal length 46.8–54.8% SL; prepelvic length 47.9–52.5% SL), triangular and small (dorsal-fin base length 13.1–18.4% SL). Caudal fin forked, symmetrical (upper caudal-fin lobe length 32.6–39.1% SL; lower caudal-fin lobe length 33.5–41.6% SL). Anal fin triangular, origin situated ⅔ down body (preanal length 64.6–70.2% SL), and small (anal-fin base length 10.5–15.2% SL). Both pelvic and pectoral fins triangular. Lateral scale series with 25–30 scales (mode 26), lateral line incomplete and leading horizontally away from head and sloping downwards, perforated lateral line scales 5–9 (mode 7). Both dorsal-fin and pelvic-fin origins on vertical through lateral scale 7–9 (mode 8) and 8–9 (mode 9) respectively, anal-fin origin at 14–16 (mode 15). Axine starting at lateral scale series 9½–11 (mode 11).

Colouration in preservative. See Fig. 7 . Base body colour cream, dorsum dark brown, with dark brown stripe across

dorsum, ventrum cream; freshly preserved specimens can be flushed orange or reddish. Head region above eye dark brown. Eye with silvery iris. Region posterior to opercle opening with distinct dark brown humeral streak. All fins hyaline, thin black margin on distal half of anterior edge of dorsal and anal fins; for freshly preserved specimens, dorsal and caudal fins orange or red, anal fin with middle portion orange, paired fins hyaline. Black axine on mid-body, anterior margin straight edged, dorsal apex starting about one scale posterior to dorsal-fin origin, ventral apex starting above pelvic-fin origin, caudal apex extending length of caudal peduncle reaching base of caudal fin; axine surrounded with distinct margin of 1–1½ scale width. Region of body anterior to triangular marking with diffused melanophores.

Colouration in life. See Figs. 1 , 4 . Base body colour orangered, dorsum can be a darker shade, belly lighter shade or silvery; sometimes with slight bluish iridescence on anterior half of body and bright orange blotch at caudal-fin base; in fully acclimatised specimens in captivity, a purplish sheen can be visible on body. Region of head above eye dark brown. Eye with orange iris with black dorsal patch and ring. Region posterior to opercular opening with diffused black humeral streak. Large velvety black axine on mid-body, anterior margin straight edged, dorsal apex at about one scale posterior to dorsal-fin origin, ventral apex at pelvic-fin origin, caudal apex extending length of caudal peduncle to caudal-fin base; whole axine with distinct margin of 1–1½ scale width. Paired fins hyaline. Dorsal fin base flushed red or orange, thin black margin on distal half of anterior edge, distal margin hyaline. Caudal fin reddish-orange with hyaline distal margin. Anal fin base hyaline, thin black margin on distal half of anterior edge, middle section sometimes with small patch of orangish-red, rest of fin hyaline. Supra-anal region to ventral base of caudal peduncle with diffused black streak.

Distribution. Trigonostigma heteromorpha is the most widely distributed species of the genus, occurring in Malay Peninsula (Perak, Selangor, Negri Sembilan, Johor, Pahang), Singapore, Sumatra (North Sumatra and Riau provinces), Riau archipelago islands of Batam, Bintan, and Lingga, Bangka island and Belitung island (see Fig. 5 ). In Sumatra, T. heteromorpha is found only in North Sumatra and Riau provinces and is replaced by T. hengeli in Jambi and South Sumatra provinces ( Kottelat & Witte, 1999; Tan & Kottelat, 2009).

Remarks. Duncker’s (1904) description of T. heteromorpha was based on material collected from Selangor, Negri Sembilan, and Singapore. Locality data for the type series was from Negri Sembilan and this had been clarified by Alfred (1963). No holotype was designated at the time of publication. Ladiges et al. (1958) selected a lectotype from Negri Sembilan, based in Zoological Museum Hamburg ( Kottelat, 2013). The locality where Duncker collected T. heteromorpha in Singapore is the Botanical Garden pond (not specified which pond) which is now depleted of T. heteromorpha as the surrounding swamp forest habitats have been destroyed. Surviving populations occur in forest streams and a remnant swamp forest habitat within the Central Catchment Nature Reserve ( Ng & Lim, 1997; Ho et al., 2016).

Both T. heteromorpha and T. truncata , new species, are the largest-sized representatives of the genus. The current largest documented T. heteromorpha is 35 mm SL ( Weber & de Beaufort, 1916: 80) and for T. truncata is 33.7 mm

SL (present study – ZRC 54736; this specimen has been kept in captivity before preservation).

Comparative material. Trigonostigma espei — ZRC 40766, 10 ex., 12.3–19.2 mm SL; Thailand: Trat Province, aquarium material; donor Kubota K, 13 January 1997 . Trigonostigma hengeli — ZRC 38687, 4 ex., 12.4–20.3 mm SL; Indonesia: Sumatra; Jambi, Pijoan , Sungai Pijoan; aquarium fish collectors, 28 May 1994 . — ZRC 37705, 18 ex., 18.8–24.4 mm SL; Indonesia: Sumatra; Jambi, aquarium material; Lim KKP et al., June 1994 . — ZRC 47139, 47 ex., 13.5–17.2 mm SL; Indonesia: Kalimantan Barat; Pontianak , aquarium trade; donor Yap P, 8 July 1998 .

Figures

Fig. 1. Trigonostigma heteromorpha with depiction of the axine (Ax) with three apices labelled. A, dorsal apex; B, ventral apex; C, caudal apex. Specimen from Singapore: Central Catchment Nature Reserve, not preserved.

Fig. 4. A, Trigonostigma truncata, new species, ZRC 54736, 33.7 mm SL, trade material; B, T. heteromorpha, ZRC 61239, 28.4 mm SL, trade material; C, T. espei, ZRC uncat, 28.2 mm SL, trade material (obese individual); D, T. hengeli, ZRC uncat, 23.3 mm SL, Sumatra: Jambi; E, T. somphongsi, not preserved, ca. 15 mm SL (right-side reversed; photograph by N. Panitvong).

Fig. 5. Trigonostigma truncata, new species, ZRC 54736, 33.7 mm SL (left); and Trigonostigma heteromorpha, ZRC 61239, 28.4 mm SL (right); detail of body, showing axine.

Fig. 7. Trigonostigma heteromorpha, BMNH 1905.5.6:2–3, paralectotypes, 22.3 mm SL (top), 23.2 mm SL (bottom); Peninsular Malaysia:Selangor (copyright of Natural History Museum,London).