This species is also referred to as ‘Kretser’s paradisefish’ and ‘spotted gourami’.

There exist three colour forms, two of which exhibit a greater degree of reddish or violet pigmentation in the fins, respectively. The third is more bluish and was described as M. kretseri minor by Deraniyagala (1958).

M. spechti is also sometimes referred to as M. concolor, particularly in older literature. A dispute regarding conservation of that name was resolved by the ICZN in 2006, however, since M. concolor Ahl, 1937 is a junior primary homonym of M. concolor Schreitmüller, 1936 and thus permanently invalid.

M. ocellatus can be distinguished from congeners by the following combination of characters: caudal-fin rounded; eye stripe not connecting spot on posterior projection of opercle with eye; dorsal-fin rays filamentous posterior to a vertical through the posterior anal-fin rays in adults; 16-19 spinous dorsal-fin rays; 6-13 rakers on ceratobranchial of first gill arch; posterior tip or margin of body scales not darker than scales.

M. opercularis is a classic aquarium fish, having been introduced to the hobby by a French soldier named Gerault in 1869. Of the initial 100 specimens shipped, 22 survived and were successfully bred later that same year by another Frenchman, the Parisian Pierre Carbonnier. This gives the species the distinction of being one of the very first ornamental fish imported to Europe. It is also known as ‘Chinese fighting fish’, ‘paradise gourami’, and ‘blue paradise fish’.

This species is sometimes sold under the trade name of 'chameleon fish' due to its ability to rapidly change colour, especially when breeding or stressed. It was originally described as Labrus badis by Hamilton but Bleeker reclassified it as Badis buchanani in 1854; he had adopted the species name 'badis' as the new name for the genus and wished to avoid using a tautonym. At that time the use of tautonyms was avoided in zoological taxonomy but is now permissible under ICZN ru…

This species lends its name to the Betta foerschi group of closely-related species within the genus, of which members share the following set of characters: possession of iridescent blue or green unpaired fins; rays and interradial membranes in unpaired fins not contrasting; dorsal fin with thin, bright white distal band; opercle with two, reddish-yellow, vertical bars.

Members are regarded as being closely-related to bubble nesting Betta specie…

This species occasionally appears in the ornamental trade where it is sometimes referred to as ‘blue tiger piranha’

Following Fink and Macaht can be distinguished from other members of the genus by the following combination of characters: body shape deep and rhomboid; head robust, snout blunt; eye large; mouth moderate, jaw projecting; 1-3 ontogeneticlly var…

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.

Famed as a rapacious predator capable of rapidly stripping flesh from bone and a danger to any animal entering its native waters, P. nattereri is among the most notorious freshwater fishes in the world. As a result, displays featuring this “bloodthirsty” creature are found in most public aquaria, grisly Hollywood movies have been released, and the species has become popular in the aquarium trade. Little of this infamy is based on factual evidence, however.

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.