All
Betta species are small fishes, but they vary considerably in size, ranging from under 2.5 cm (1 in) total length in
B. chanoides to 14 cm (5.5 in) in the Akar betta (
B. akarensis). The bettas exhibit two kinds of spawning behaviour: some build
bubble nests, such as
B. splendens, while others are
mouthbrooders, such as
B. picta. The mouthbrooding species are sometimes called "pseudo bettas", and are sometimes speculated to have
evolved from the nest-builders in an
adaptation to their fast-moving stream habitats. A phylogenetic study published in 2004 concluded tentatively that bubble-nesting was the ancestral condition in
Betta, and that mouthbrooding has evolved on more than one occasion in the history of the genus. However, it was unable to establish a correlation with any of three habitat variables studied: whether a species was found in lowland or highland streams, whether it was found in
peat swamp forests, and whether it was found in water with fast or slow currents. Mouthbrooding species tend to exhibit less sexual dimorphism, perhaps because they do not need to defend a territory as the bubble-nesters do. ==Name==