Betta omega, Hui & Ahmad, 2018

Hui, Tan Heok & Ahmad, Amirrudin Bin, 2018, Betta omega, a new species of black water fighting fish (Teleostei: Osphronemidae) from Malaysia, Raffles Bulletin of Zoology 66, pp. 402-407 : 403-406

Betta omega , new species

( Figs. 1–3 )

Betta macrophthalma (non-Regan, 1910) – Schmidt, 1988: 341 (illustrated in Kottelat et al., 1993: pl. 77).

Material examined. – Holotype: ZRC 59663, 70.0 mm SL; Peninsular Malaysia: Johor: Pekan Nanas area , Sungai Burong near Jeram Batu; J. J. Foo, 19 Feb 2016.

Paratypes: ZRC 59664, 1 ex., 74.0 mm SL; same locality data as holotype . – ZRC 59665, 3 ex., 60.4-81.2 mm SL; Peninsular Malaysia: Johor: Pekan Nanas area ; Allan & Barbara Brown, (preserved in) 1984 .

Non-type material: ZRC 59666, 14 ex., 30.1–35.1 mm SL ; ZRC 59667, 9 ex., 69.5–79.2 mm SL; Peninsular Malaysia: Johor: Pekan Nanas area ; F1 generation from wild caught individuals; Allan & Barbara Brown, (preserved in) 1988 .

Diagnosis. Betta omega can be distinguished from other members of the B. waseri group in having the following combination of characters: black markings on lower jaw continuous with two black downward curved bars on throat, ending with rounded bulging ends near edge of lower jaw (vertical line projection downwards from lower jaw posterior end; see Fig. 4i ); opercle uniform brown with light dark brown mottling, operculum without lower distal margin black; black transverse bars on the dorsal and caudal fin interradial membranes; absence of a dark distal border on anal fin.

Betta omega differs from its putative closest relative B. hipposideros in having an omega (Ω) pattern on throat (vs. downward slender black bars, resembling a horseshoe shape), lateral scale 15 below the dorsal-fin origin (vs. mode 16), lateral scale 6 above the anal-fin origin (vs. mode 7) and postdorsal scales 10–12, mode 11 (vs. 9–10, mode 9½).

Description. General body form as in Figs. 1 , 2 ; meristic and morphometric information listed in Table 1. Body relatively long and stout (body depth at dorsal-fin origin 27.1–28.5% SL); head stout with pointed snout and evenly sloping or with slight convexity at supra-orbital area (head length 28.4–32.1% SL); dorsal fin pointed, situated nearer to caudal fin (predorsal length 62.2–68.9% SL), dorsal-fin base short (dorsal fin base length 12.6–15.4% SL), covering 6½ subdorsal scales; caudal fin rounded with middle rays elongate; anal fin with posterior rays elongate, anal fin base more than half of SL (anal-fin base length 55.3–60.7% SL); pelvic fin falcate with first ray filamentous, relatively long (pelvic fin length 29.8–36.4% SL), reaching up to base of 12th anal fin ray; pectoral fin rounded.

Vertebral count: 10–11 + 19–21 (total 29–32, mode 31 or 32, n=5).

Live colouration. See Figs. 1 , 3 for live colouration.

Head and dorsum of body brown. Eye with unique colouration zones of the B. waseri group (as defined by Tan, 1998). Mouth with lower and upper lips black, lower jaw black, black marking continuous with two black downward curved bars on throat, ending with bulging rounded tips around near edge of lower jaw (vertical line projection downwards from lower jaw posterior end). Opercle with faint greenish-yellow individuals were caught along every few meters of the ditch, possibly an indication of the territorial behaviour of the fish (Benel Tang, pers. comm.). Syntopic fish species included: Desmopuntius hexazona , Rasbora einthovenii (Cyprinidae) , Monopterus javanensis (Synbranchidae) , Betta bellica , B. pulchra (Osphronemidae) , and Channa lucius (Channidae) .

Etymology. From the Greek Omega / Ω (upper case), the last letter of the Greek alphabet; in allusion to the unique throat pattern and in reference to the last members of this species in the quickly disappearing black water habitat type in Malaysia and Southeast Asia. Used as a noun in apposition.

Remarks. Betta omega can be distinguished further from B. waseri in the following characters: “Ω /omega” shape throat pattern (vs. two tear-drop shaped black marks below but not connected to black lower lip; see Fig. 4 ); absence of black lower margin of operculum (vs. presence); opercle without any distinct brown markings and with light greenish-yellow iridescence (vs. several short black streaks, and without iridescence); deeper body (27.1–28.5% SL, vs. 23.1–27.6); dorsal fin begins at lateral scale 15 (vs. 17–18); anterior anal-fin base at vertical through lateral scale 6 (vs. 8–9).

iridescence, iridescence extending to side of body (up to 10 scale rows) above belly area. Body yellowish-brown, with faint dark patches just above anal fin sheath scales. Dorsal fin brownish with up to 10 transverse bars on interradial membranes. Caudal fin brownish with up to 24 transverse bars on interradial membranes. Anal fin brownish, without distal dark border but with narrow white margin. Pelvic fin yellowish-brown with whitish interradial membranes, distal part of filamentous pelvic-fin ray iridescent whitish-green. Pectoral fin hyaline with black sub-basal bar.

Preserved colouration. Preserved colouration illustrated in Fig. 2 . Head and body dorsum dark brown. Opercle area with brown mottling. Throat pattern indistinct. Lateral of body with indistinct brown central stripe. Faint brown stripe above anal-fin base. Rest of body yellowish-brown on lateral and cream-yellow on ventrum. Fin rays light brownish and rest hyaline.

Distribution. Betta omega is recorded only from the remnant black water habitats near Pekan Nanas in Johor, Peninsular Malaysia. There is a likelihood that this species is near extinction or already extinct.

Field notes. The habitat of Betta omega was located in remnant black water swamps, present as roadside ditches along the Pontian Kecil-Pekan Nanas road; also as small streams flowing through oil palm estates. These dug ditches are usually overgrown with vegetation. Fishes were caught using a simple earthworm-baited hand-line. Only a few Betta omega can be further distinguished from B. tomi in the following characters: “Ω /omega” shape throat pattern (vs. throat with two black oval spots which do not merge with black lower lip; see Fig. 4 ); absence of black lower margin of operculum (vs. presence); opercle without any distinct brown markings and with light greenish-yellow iridescence (vs. several short black streaks, and without iridescence); distal margin of anal fin without black or coloured band (vs. presence); anterior anal-fin base at vertical through lateral scale 6 (vs. 7–8); subdorsal scales 6½ (vs. 5–5½); postdorsal scales 10–12, mode 11 (vs. 10–10½, mode 10).

Betta omega can be further distinguished from B. spilotogena in the following characters: “Ω /omega” shape throat pattern (vs. throat with two very broad black oval spots which may appear joined medially, spots do not merge with black lower lip; see Fig. 4 ); absence of black lower margin of operculum (vs. presence); opercle without any distinct brown markings and with light greenish-yellow iridescence (vs. distinctly covered with several large black spots, without iridescence); anterior anal-fin base at vertical through lateral scale 6 (vs. 7–8, mode 7); subdorsal scales 6½ (vs. 5½–6, mode 5½).

Betta omega can be further distinguished from B. chloropharynx and B. pardalotos in the following characters: “Ω /omega” shape throat pattern (vs. throat with two cream blotches on a black throat; see Fig. 4 ); opercle without any distinct brown markings and with light greenish-yellow iridescence (vs. heavily spotted opercle of B. pardalotos ).

Betta omega can be further distinguished from B. pi in the following characters: “Ω /omega” shape throat pattern (vs. throat with π-shaped black pattern; see Fig. 4 ); opercle without any distinct brown markings and with light greenishyellow iridescence (vs. opercle with several black blotches of variable size, without iridescence); distal margin of anal

fin without black or coloured band (vs. presence); shorter head length (28.4–32.1% SL, vs. 32.3–34.4); deeper caudal peduncle depth (19.2–20.6% SL, vs. 16.3–18.4); subdorsal scales 6 ½ (vs. 5½–6, mode 6).

Betta omega can be further distinguished from B. renata in the following characters: “Ω /omega” shape throat pattern (vs. a kidney-shaped black mark on throat, not connected with black lower lip; see Fig. 4 ); opercle without any distinct

brown markings and with light greenish-yellow iridescence (vs. several black spots on opercle); absence of black lower margin of operculum (vs. presence).

Figures

Fig. 1. Betta omega, new species – ZRC 59663, 70.0 mm SL holotype, life colouration (photograph by Z. Zakaria).

Fig. 2. Betta omega, new species – ZRC 59663, 70.0 mm SL holotype, preserved specimen.

Fig. 3. Betta omega, new species – ZRC 59664, 74.0 mm SL paratype, front view of head showing lower jaw and throat pattern (photograph by Z. Zakaria).

Fig. 4. Schematic diagrams of throat patterns of the Betta waseri species group. a, B. waseri; b, B. hipposideros; c, B. tomi; d, B. spilotogena; e, B. chloropharynx; f, B. renata; g, B. pi; h, B. pardalatos; i, B. omega.