Every species

This species is included in the Betta unimaculata complex of closely-related species within the genus, of which members share the following set of characters: body long and slender with depth at dorsal fin origin 18-25 % SL; head large and blunt with width 19-24 % SL; long maxilla and lower lip with distance from tip of lower jaw to poste...

B. persephone can be told apart from other members of the group by the following characters: no lateral blotch; body blackish; dorsal surface of head posterior to eye sloping gently; no parallel vertical iridescent gold opercle bars; pelvic-fin falcate with white filamentous tip, remainder black to reddish; median fins covered diffusely with light green iridescence; dorsal fin-rays 9; anal-fin rays 24-27; subdorsal scales 6-7; lateral scales 27-29; predorsal scales 17-18.

B. pi is included in the Betta waseri group of closely-related species within the genus, an assemblage within which members share the following combination of characters: base body colouration clay yellow; opercle scales iridescent gold in mature males of all species except B. tomi; throat with black markings which join with black lower jaw in some species; no chin bar.

This species lends its name to the Betta picta complex of closely-related species, an assemblage of which members share the following combination of characters: unpaired fins rounded (anal fin sometimes pointed): I-III, 18-24 anal-fin rays; anal and caudal fins with dark distal margins, most pronounced in mature males; pre- and post-orbital stripes present; chin bar present; opercle with iridescent blue, green, or gold scales.

B. pinguis is included in the Betta akarensis group/complex of closely-related species within the genus, of which members share the following set of characters: possession of pre-orbital and post-orbital stripes (the post-orbital stripe is faint or interrupted in some species); chin bar present; caudal-fin lanceolate with highly extended median rays in mature males; caudal fin usually with transverse bars; greenish or bluish iridescent scales on body of males in some species; opercle without iridescent scales except in juveniles.

It can be told apart from other members of the B. pugnax group by the following characters: second postorbital stripe on opercle complete; no transverse bars in caudal-fin; 20-22 predorsal scales; preanal length 50.6-54.8 % SL. Not all authors consider it a member of this group, however, with some placing it in the B. picta complex, e.g., Schindler and Schmidt (2006). The genus is th...

It can be told apart from other members of the B. pugnax group by the following characters: chin bar present; no complete second postorbital stripe on opercle; presence of transverse bars in caudal-fin of males; caudal-fin in males broadly lanceolate; opercle scales iridescent blue; anal-fin with reddish subdistal band and black margin; caudal-fin without dark margin; 25-28 anal-fin rays; 28-31 lateral scales; 11-12 postdorsal scales; length of pelvic fins 26.6-43.8 % SL; length of head 27.5-35.2 % SL; inter-orbital width 32.4-53.0 % HL.

Restricted to remnant blackwater habits in heavily-disturbed areas of former peat swamp forest, the original vegetation having been cleared to make space for plantations of oil pal, pineapple and rubber. It's now typically found among overhanging marginal vegetation of irrigation canals, with sympatric species including Belontia hasseltii, Betta bellica, B. imbellis, Sphaerichthys osphromenoides, Parosphromenus sp., and Trichopsis vittata. PH in its natural waters has been recorded over the range 3.9 - 4.2.

It should be noted that not all authors consider the B. pugnax group to contain the same species, with some placed in the B. picta complex by Schindler and Schmidt (2006), for example. B. raja can be told apart from other members of the B. pugnax group by the following characters: mature males with very long pelvic fins covering 15-23 anal-fin rays or even longer than the base of the anal-fin in some cases; anal-fin and lower caudal-fin with black marginal bands; 25-28 anal-fin rays; 30-32 lat...

This species is included in the Betta waseri group/complex of closely-related species within the genus, an assemblage which also includes a handful of potentially new species such as B. sp. 'Medas' on an unofficial basis. Group members share the following combination of characters: base body colouration clay yellow; opercle scales iridescent gold in mature males of all species except B. tomi; throat with black markings which join with black lower jaw in some species; no chin bar.

This species was previously included in the Betta foerschi group of closely-related species within the genus, but following its redescription in 2012 now lends its name to the B. rubra group. It was first placed into its own species group by Witte and Schmidt (1992), primarily on the basis of a triangular marking that appears below the eyes of the fish, although Tan and Ng (2005) suggested that this feature is insufficient to warrant the fo...

This species is included in the B. coccina group/complex of closely-related Betta species within the genus. This assemblage mostly comprises small, red-coloured fishes, with the exceptions of B. persephone and B. miniopinna which are darkish, and identifying some of them can be problematic as external patterning can be both similar and confusingly variable.

This species was considered a colour form of the closely-related B. imbellis and commonly-referred to as 'black imbellis' prior to description due to its blackish opercle and body. It's also previously been confused with B. splendens due to the colour of the vertical opercular bars which tend to be reddish (but may also be pale red, greenish-silvery, plain silvery or without colour in some populations), but DNA analysis has demonstrated it...

This species is included in the B. bellica group/complex of closely-related species within the genus, an assemblage of which members share the following set of characters: long and slender body with dorsal and ventral margins almost parallel; body depth 23-28 % SL; 30-33 anal-fin rays; 11-13 dorsal-fin rays; 32-34 total vertebrae; body dark brown in colour with iridescent green markings on each individual scale.

B. simplex is included in the Betta picta group/complex of closely-related species within the genus, an assemblage comprising species with the following shared characters: unpaired fins rounded (anal-fin sometimes tapering to a blunt point); anal-fin rays I-III, 18-24; dark marginal band on anal and caudal fins, more pronounced in mature males; presence of pre-orbital and post-orbital stripes; presence of chin bar on throat; iridescent green, gold, or blue scales on opercle.

This species is included in the Betta splendens complex of closely-related species within the genus, of which members share the following set of characters: head length short 22-31 % SL; often a brightly-coloured body; iris of the eye with iridescent green or blue patches; body elongate or slender; opercles parallel when head viewed dorsally; caudal-fin rays red or brown and contrasting with the iridescent interradial membranes; unpaired fins without an iridescent margin; opercle with red or blue vertical bars in males; dorsal-fin rays 0-II, 7-9; anal-fin rays II-V, 21-26.

This hypothetically-undescribed species appears to be a member of the Betta unimaculata complex of closely-related species within the genus, of which members share the following set of characters: body long and slender with depth at dorsal fin origin 18-25 % SL; head large and blunt with width 19-24 % SL; long maxilla and lower lip with distance from tip of lower jaw to posterior end of maxilla 27-54 % HL; caudal-fin rounded in shape, occasionally with elongated median rays; pelvic-fin short and filamentous; dorsal and anal fins relatively pointed.

Inhabits freshwater swamps and associated streams, typically shaded from the sun by dense riparian vegetation. The water is normally clear or lightly stained with tannins, and the fish found in water less than a metre deep alongside related species including Betta edithae, B. miniopinna, and B. fusca. PH has been measured to range between 4.9-5.5.

This species' common name is derived from the tradition of keeping the fish in order to fight against each other in organised 'bouts' upon which participants and onlookers place wagers. It has been extensively line-bred for vigour, strength, and the ornamental trade, and hybridised with the congeners B. imbellis, B. smaragdina, and B. mahachaiensis.

Known only forest hill streams with flowing, clear water. These are typically shaded from the sun by dense riparian vegetation. The substrate is composed of rocks or gravel, fallen leaves, branches and submerged tree roots, and presumably the fish show a preference for quieter marginal zones as with related congeners. The type locality was described as a 'swampy stream' and sympatric species incl...