Anabantoidei

The Anabantoidei are a suborder of anabantiform ray-finned freshwater fish distinguished by their possession of a lung-like labyrinth organ, which enables them to breathe air. The fish in the Anabantoidei suborder are known as anabantoids or labyrinth fish, or colloquially as gouramies. Some labyrinth fish are important food fish, and many others, such as the Siamese fighting fish and paradise fish, are popular as aquarium fish. The labyrinth organ, a defining characteristic of fish in the suborder Anabantoidei, is a much-folded suprabranchial accessory breathing organ. It is formed by vascularized expansion of the epibranchial bone of the first gill arch and used for respiration in air. This organ allows labyrinth fish to take in oxygen directly from the air, instead of taking it from the water in which they reside through use of gills. The labyrinth organ helps the inhaled oxygen to be absorbed into the bloodstream. As a result, labyrinth fish can survive for a short period of time out of water, as they can inhale the air around them, provided they stay moist. Labyrinth fish are not born with functional labyrinth organs. The development of the organ is gradual and most labyrinth fish breathe entirely with their gills and develop the labyrinth organs when they grow older. Labyrinth fish are endemic to fresh waters of Asia and Africa. In Asia, they are found throughout East, Southeast, and South Asia, especially but not exclusively in the warm, slow-flowing, low-oxygen waters. In Africa, significantly smaller numbers of labyrinth fish can be found in the southern half of the continent, with concentrations in the rainforest waters. The characteristics of the fish habitats are indicators of the size of the labyrinth organ, as the organ size is negatively correlated with the level of oxygen in the waters. Species native to low-oxygen waters are more likely to have larger and more complex labyrinth organs than species found in fast-flowing, oxygen-rich waters. In general, the labyrinth fish are carnivores that eat small aquatic organisms and carrion. Some species will also consume algae and water plants. Most fish are active during daytime, but several African species feed at twilight and night. Species of the genus Trichogaster can spit water toward insects to bring them down to the water surface, similarly to the archerfish behavior. Labyrinth fish are well known for their bubble-nesting behavior, although some species do not build bubble nests and employ other methods of brooding. For the bubble nesting species, males establish nesting territories and defend them vigorously. As the name suggests, the bubble nests are floating bubbles coated with oral mucus from the males. Typically, the male bubble nesters stay nearby to guard the nests and constantly retrieve any falling eggs and fry to the nest. Some Betta species from fast-flowing waters, however, are mouthbrooders and do not build bubble nests. In these species, males hold the eggs and fry in their mouths and release the free-swimming fry about a week to 10 days after spawning.