Betta nuluhon, Kamal & Tan & Ng, 2020

Kamal, N. S. S., Tan, H. H. & Ng, Casey K. C., 2020, Betta nuluhon, a new species of fighting fish from western Sabah, Malaysia (Teleostei: Osphronemidae), Zootaxa 4819 (1), pp. 187-194 : 188-192

Betta nuluhon , new species

Figs. 1–4

Material examined. Holotype—ZRC 61247, 62.6 mm SL, male; Sabah: Crocker Range Forest Reserve; Kamal N. S. S. et al., Nov 2019.

Paratypes. FRC 0162 , 5 ex. , ZRC 61154, 5 ex. , 39.8–54.0 mm SL; same locality data as holotype . FRC 0161 , 3 ex. , ZRC 57026, 3 ex. , 46.0– 57.4 mm SL; Sabah: Crocker Range Forest Reserve ; Kamal N. S. S. et al., April 2018 .

Diagnosis. Betta nuluhon is distinct from its congeners in the B. akarensis group in having the following unique combination of characters: yellow iris when live; mature males with greenish-blue iridescence on opercle when live; mature fish with distinct transverse bars on caudal fin; slender body (body depth 22.1–25.2 % SL); belly area with faint reticulate pattern (posterior margin of scales rimmed with black); anal-fin plain; lateral scales 29–31; predorsal scales 20–21.

Description. See Figs. 1–4 for general appearance. See Table 1 for meristic and morphometric data of B. nuluhon .

Head broad, blunt, short (head length 31.7–35.2 % SL); body cylindrical in cross-section anteriorly, becoming compressed at dorsal-fin origin to caudal region; body deepest at dorsal-fin origin (22.1–25.2 % SL), shallowest in caudal peduncle (16.4–20.0 % SL); dorsal-fin rays I, 7 (total 8), pointed, situated at about ⅔ head-and-body length (predorsal length 65.8–71.3 % SL), dorsal-fin base short (10.6–13.5 % SL); caudal-fin lanceolate, with 5+6 principal rays, middle rays elongated slightly beyond interradial membrane margin; anal-fin with I–II, 25–27 (total 26–28) rays, pointed, situated around ½ body (preanal length 45.4–49.7 % SL), anal-fin base long (49.5–54.6 % SL); pelvic-fin with i, 5 rays, rounded, with filamentous second ray, adpressed filamentous ray reaching 13 th analfin ray (pelvic-fin length 31.5–45.1 % SL); pectoral-fin rays 13–14, rounded; lateral scales 29–31, predorsal scales 20–21, subdorsal scales 5½–6½, postdorsal scales 10–11, transverse scales 9½. Vertebral count 11–12 + 19–20, total vertebrae = 31 (n =6).

Fresh colouration. See Figs. 1 , 2 , 4 . Head brown, dorsum dark brown; dark brown to black preorbital stripe running from upper jaw through eye to postorbital to opercle edge; black chin bar present, dark brown suborbital stripe present; eye with dorsal region of iris yellow, lateral regions black, bottom region reddish; mature male with whole throat area dark brown, sometimes with greenish-blue iridescence; female and juvenile with brown throat; body brown, dorsum dark brown, posterior edge of body scales along flank rimmed with bright blue; all fins brownish, dorsal fin with 4 to 6 black transverse bars, caudal fin with 12 to 16 black transverse bars, anal fin with broad reddish-brown margin, pelvic fin with whitish filamentous ray.

Preserved colouration. See Fig. 3 . Head brown, dorsum dark brown, black preorbital stripe running from upper jaw through eye to postorbital to opercular edge, black chin bar present, dark brown suborbital stripe present with pigments along opercle edge (pattern similar to Betta chini , see Tan & Ng, 2005: 49, Fig. 7c); mature male with whole throat area diffused with brown; female and juvenile with throat area light brown; body brown, dorsum dark brown; belly area cream with light brown reticulate pattern from posterior edge of scales bearing darker pigments; all fins brownish except hyaline pectoral fin, dorsal fin with 4 to 6 black transverse bars, caudal fin with 12 to 16 black transverse bars, anal fin reddish-brown, pelvic fin with white filamentous ray.

Field notes. Specimens were collected from the velocity refugia of a shallow (knee level) clear-water stream with overhanging bank vegetation in Crocker Range Forest Reserve’s closed-canopy forest fringe area. The substrate was composed mainly of pebbles, sand and silt. Some water parameters were recorded: dissolved oxygen 6.25 mg /L, pH 6.57, suspended solids 0.4 mg /L, turbidity 28.0 FAU, temperature 24.0° C. Syntopic species include: Anguilla marmorata Quoy & Gaimard (Anguillidae) , Barbodes sealei Herre , Nematabramis borneensis Inger & Chin , Tor tambra Valenciennes, in Cuvier & Valenciennes (Cyprinidae) , and Gastromyzon introrsus Tan (Gastromyzontidae) .

Etymology. This new species is named for the Kadazandusun vernacular nuluhon , meaning hill. This pertains to its hill stream habitat. Used as a noun in apposition.

Remarks. Betta nuluhon can be distinguished from similar species from the geographic vicinity ( B. akarensis , B. balunga and B. chini ) in the following characters: gently sloping anterior body dorsum profile (vs. convex profile of B. balunga and B. chini ); absence of tiny black spots on anal fin (vs. presence of many tiny black spots in B. chini ); shallower body depth than B. akarensis and B. balunga (22.1–25.2 % SL, vs. 23.5–27.9 and 28.0–31.5, respectively); shorter preanal length than B. balunga (45.4–49.7 % SL, vs. 49.2–52.2); shorter dorsal-fin base length than B. balunga (10.6–13.5 % SL, vs. 13.7–14.1); smaller orbit diameter than B. balunga (23.3–29.7 % SL, vs. 29.5–33.3).

Betta nuluhon can be differentiated from the other members of the B. akarensis group in the following characters:

From B. antoni —deeper body (22.1–25.2 % SL, vs. 20.6–22.9); fewer lateral scales (29–31, vs. 31–33); fewer predorsal scales (20–21, vs. 23–24). From B. aurigans —shallower body (22.1–25.2 % SL, vs. 25.2–27.4); fewer lateral scales (29–31, vs. 33–33½); fewer predorsal scales (20–21, vs. 24–26); fewer anal-fin rays (26–28, vs. 29–30). From B. ibanorum —more patterned opercle (vs. less patterned); lower range of lateral scales (29–31, vs. 30–32); fewer predorsal scales (20–21, vs. 21–23).From B. obscura —shallower body (22.1–25.2 % SL, vs. 28.7–32.7). From B. pinguis —less pigmented opercle (vs. heavily pigmented); shallower body (22.1–25.2 % SL, vs. 30.6–31.6); fewer lateral scales (29–31, vs. 31½–32½); fewer predorsal scales (20–21, vs. 23–24) (data obtained from Tan & Kottelat, 1998; Tan & Lim, 2004; Tan & Ng, 2004; 2005; 2006).

The recent collection of Betta chini (ZRC 61155; see Figs. 4–5 ) from Klias Forest Reserve indicates that there is still a viable population. The heath and peat swamp forest habitat had been badly burnt previously, during the El- Niño fires of 1998 ( Phua et al., 2007), and there was suspicion the species may have become extinct. Betta chini is now assessed as Endangered by the International Union for Conservation of Nature ( Low, 2019).

When B. chini was described, the largest specimen recorded was 56.0 mm SL (ZRC 35088; see Ng, 1993: 290). The recent series contains five specimens (out of ten) ranging from 57.5 to 62.5 mm SL, which indicate that the present series maybe occupying a preferred micro-habitat; as the type series had been obtained from peripheral streams of the reserve. All specimens of the recently-collected series have stocky bodies, with a convex body dorsum profile (see Fig. 5 ), similar to the range of values of body depth and caudal peduncle depth of B. nuluhon (see Table 2). From these values, the body shapes of both B. chini and B. nuluhon may be expected to be more similar, but they are distinctly different (see Figs. 3–5 ).

Figures

FIGURE 1. Betta nuluhon, new species, ca. 50 mm SL, freshly caught male specimen, not preserved.

FIGURE 2. Betta nuluhon, new species, male (top), female (bottom); freshly caught, not preserved.

FIGURE 3. Betta nuluhon, new species, ZRC 61247, holotype, 62.6 mm SL (above with white background, bottom with black background).

FIGURE 4. Top—Betta chini, ZRC 61155, 58.6 mm SL male; bottom—Betta nuluhon, holotype, ZRC 61247, 62.6 mm SL male; both freshly preserved.

FIGURE 5. Betta chini, ZRC 61155, 58.6 mm SL; Sabah: Klias Forest Reserve (right side, laterally inverted) (above with white background, bottom with black background).