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.