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. falx 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.

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 was traded as B. sp. ‘Kapuas’ prior to its formal description and continues to be mislabelled B. dimidiata. The two can easily be told apart as the caudal-fin is rounded in B. krataios but spade-shaped and in adults, highly-extended in B. dimidiata.

Together these two comprise the B. dimidiata group/complex of closely-related species within the genus, members of which can be characterised b…

B. macrostoma 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 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.

B. ibanorum is uncommon in the hobby and is apparently more frequently fished for food than the aquarium trade. It’s 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 lance…

B. chloropharynx 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. The easiest way to distinguish these is by examining the throat markings which vary according to species.

In this case the lighter of these form a shape that roughly resembles a horizontal figure of ei…

This species is relatively rare in the aquarium trade.

It can be differentiated from all congeners by a combination of possessing ctenoid (vs. cycloid) scales on the sides of the head plus lacking a dark spot at the caudal-fin base.

The precise extent of this species’ range is unclear. The majority of records pertain to the lower rio Xingu basin in the state of Pará, northern Brazil, including middle and lower reaches of its major tributary the rio Iriri, although the type locality is in Mato Grosso state several hundred kilometres upstream.

There also exist a handful of records from the rio Jamanxim (a major affluent of the rio Tapajós which drain…