Betta mulyadii, Ding & Lei & Haryono & Shi & Zhang, 2025

Betta mulyadii sp. nov.

Figs 5 View Figure 5 , 6 View Figure 6 , Suppl. material 2: fig. S 2

Betta sp. Riau Red — Linke 2014: 228.

Type material.

Holotype. MZB.26964 , 18.5 mm SL, male; Indonesia, Sumatra Island, Riau, Oil palm plantation; colls. Mulyadi Tjoa Hong Tjai, Nov. 2023 . The exact locality withheld to avoid potential pressure on the wild population of ornamental fish industry. Qualified researchers can request information from the first author or MZB. Paratypes. NCUMB.65326 , 28 specimens, 22.4–28.4 mm SL; same data as for holotype; colls. Mulyadi Tjoa Hong Tjai & Johan Raharjo. Jun. 2022 .

Diagnosis.

Betta mulyadii sp. nov. differs from its congeners in the B. coccina group by the following unique combination of characters: fewer dorsal-fin rays (8 * – 10) and subdorsal scales (5 * - 6); shorter dorsal-fin base (9.89–15.1 % SL, mean 12.5 %); male with reddish body; without green iridescent mid-lateral body patch; unpaired fins red without significant marks (dorsal and caudal fins with bright bluish margins).

Description.

Morphometric and meristic data are summarized in Table 1 View Table 1 . General appearances presented in Fig. 5 View Figure 5 . Head rounded and small. Body slender (at dorsal-fin origin 18.7 % – 22.0 % SL, mean 19.9 %), not compressed at caudal peduncle (12.9 % – 16.5 % SL). Dorsal fin narrow (total 8 * – 10 rays), base short (9.89–15.1 % SL with 5 * – 6 subdorsal scales) and placed significantly far back (predorsal length 58.1–65.9 % SL). Dorsal fin pointed with elongated posterior rays, sometimes reaching caudal-fin base in mature males. Anal fin situated ~ ½ body (preanal length 38.1 % – 43.5 % SL), base long (48.9 % – 58.9 % SL). Anal fin with total 27 * – 29 rays, pointed, posterior rays elongated, sometimes reach half-length of caudal fin in mature males. Caudal fin lanceolate in males, rounded in females, with i-ii rudimentary, I simple principal, 4 + 5 branched principal, I simple principal, i-ii rudimentary rays (modal i-I- 4 + 5 - I-i). Pectoral fin rounded with (12–14, modal 13) rays. Pelvic fin with one spine, one simple and four branched rays, simple ray filamentous. Lateral scales 29–30 *, plus two or three scales on caudal-fin base; predorsal scales 19–21 *; postdorsal scales 9–12 (modal 10); 7–8 * scales in transverse series at dorsal fin origin.

Live coloration.

Male (Fig. 5 B, C, E View Figure 5 ). Head reddish with iridescent greenish / golden patches, dorsum reddish with iridescent greenish / golden patches. Opercle without distinct bar in neutral mood, two barely recognizable pale reddish twin bars on opercle in aggressive or breeding mood. Iris with iridescent bluish patches. Body uniformly reddish with weak iridescent blue patches on some scales (absent in stressed or preserved specimens), dorsum reddish with iridescent greenish / golden patches. No distinct dark stripes or iridescent patches on body flank. Dorsal-fin simply red with a bright bluish margin. Caudal fin simple red with a bright bluish margin on the upper half (sometimes also present on the lower half). Anal fin simply red (rarely with a bluish margin). Pectoral fin hyaline. Pelvic fin red with whitish filamentous ray.

Female (Fig. 5 D View Figure 5 ). Head and body coloration similar to male, but less reddish. All fin colorations similar to male, but bluish margin less distinct.

Preserved coloration.

Male (Suppl. material 2: fig. S 2): Head yellowish brown, dorsum brownish, no bar present on opercle. Body and dorsum uniformly yellowish brown. Unpaired fin uniformly dark reddish without distinct margin. Pectoral fin hyaline. Pelvic fin red with hyaline filamentous ray.

Female (Suppl. material 2: fig. S 2): Head and body coloration similar to male. All fin colorations similar to male, but more brownish.

Comparison.

Betta mulyadii sp. nov. can be easily distinguished from the closely related phylogenetic sister species Betta iaspis sp. nov. by the following combination of characters: uniformly reddish body (vs blackish), simple reddish anal fin (vs blackish with reddish patches on posterior part), dorsal-fin inter-radial membrane without dark marks (vs present). It is also distinct from other congeners of the same phylogenetic branch B. persephone and B. miniopinna by the presence of red dorsal- and caudal fins (vs dark greenish / bluish); filamentous elongated posterior rays of anal fin (vs pointed but not filamentous). It differs from its most morphologically similar species B. rutilans by the presence of a bright bluish margin on dorsal and anal fins (vs absence / indistinct), elongated anal-fin posterior rays reaching half-length of caudal fin in mature males (vs slightly pointed but not significantly elongated), fewer dorsal-fin rays (8 * – 10 vs 11–12 *), fewer subdorsal scales (5 * – 6 vs 9 * – 10) and shorter dorsal-fin base (7.5–19.1 % SL vs 20–23 %). It also differs from B. burdigala , B. coccina , B. livida , B. tussyae , and B. uberis by lack of iridescent greenish / bluish streaks / patches on inter-radial membrane of unpaired fins (vs presence); differs further from B. burdigala and B. uberis by fewer dorsal-fin rays (8 * – 10 vs 14–17), from B. coccina by whitish pelvic-fin tips (vs black), from B. livida and B. tussyae by fewer lateral scales (29 * – 30 vs 30–31). It can be differentiated from B. brownorum by the lack of an iridescent mid-lateral blotch (vs presence); from B. hendra by a reddish body and fins (vs iridescent bluish / greenish), absence of distinct bar on opercle (vs prominent red parallel bars), fewer transverse scales 7–8 * (vs 8–10).

Distribution.

Betta mulyadii sp. nov. is currently known only from an area in Riau, Sumatra Island (Fig. 1 View Figure 1 ).

Etymology.

The species is named after Mulyadi Tjoa Hong Tjai, who discovered this species and contributed much first-hand field information on this genus during the last 30 years. Previously the species was widely known by the common name “ api-api ” given by the discoverer, which means flame / fire in Bahasa Indonesia referring to the reddish body and lanceolate caudal fin.

Field notes.

The species was first recorded by Mulyadi Tjoa Hong Tjai in Duri in 2012. Currently it is still only found in this area, which is severely disturbed by human activities. Most of the nearby regions have been converted into oil-palm plantations or occupied by oil wells. Thus, we have not yet been able to record this species outside the type locality, which is a broken tiny swamp located inside an oil-palm plantation and adjacent to several running oil wells (Fig. 6 View Figure 6 ). Further studies will be necessary to explore potential remaining population and habitats of this endangered species.

All the syntopic fish species recorded from the habitats include Betta cf. pugnax ( Tan & Ng, 2005) and Rasbora einthovenii .

Conservation status.

Oil-palm plantations and the petroleum industry have severely destroyed the environment in Duri, especially forest peat swamps. During the field survey in 2023, little original forest peat swamps could be found in this region. The type locality of the new species is in poor condition, original forest no longer exists, and the remaining swamp is shaded by secondary shrubs. Biodiversity is very low, which is expected since it is inside a large oil-palm plantation (Fig. 6 B View Figure 6 ). Few conservation efforts for freshwater fish are known there, since it is also a petroleum industry area. Immediate in-situ and ex-situ conservation is highly recommended for this species. Thus, following the IUCN Red List Categories and Criteria (v. 3.1), we propose Betta mulyadii sp. nov. be listed as Critically Endangered B 2 ab (iii), based on its very restricted distribution area in a single swamp (<5 km 2) and the extremely high likelihood of becoming extinct due to the current existence of surrounding oil-palm plantations and oil wells.

Molecular analysis.

The consensus phylogenetic tree based on the mitochondrial Cyt b suggests that Betta mulyadii sp. nov. is a monophyletic group distinct from its sister group Betta iaspis sp. nov. by an uncorrected p-distance of 4.35 % (Fig. 7 View Figure 7 ; Suppl. material 1: table S 2). Betta mulyadii sp. nov. is also distinct from other congeners in the same branch for which Cyt b is available with a p-distance ranging from 5.75 % to 7.19 % (Suppl. material 1: table S 2), and distinguished from the remaining species in the other branch with a p-distance ranging from 19.2 % – 22.0 % (Suppl. material 1: table S 2). These results suggest that genetic differences among the new species and its congeners are indicative of divergence at a species level. Betta mulyadii sp. nov. also differs from all known Betta species in its unique morphological characters (see above Diagnosis and Comparison). Thus, based on both molecular and morphological analysis in the current study, this fish from Riau, Sumatra is formally recognized as a distinct species.