The popular aquarium fishes betta, gourami, and the Paradise Fish are known as anabantoids [often seen as anabantids], or scientifically, Anabantoidei, a suborder of the order Perciformes. The name Perciformes is derived from the Greek perke [perch] and the Latin forma [shape]. The order contains approximately 40% of all bony fish and is the largest order among all the vertebrates; it is also the most variably sized order, having members as small as 7 millimeters (just over 1/4 inch) to as large as 5 metres (16.4 feet). They first appeared and diversified in the late Cretacious period. There are 156 families in 18 sub-orders; most of the more than 7,000 species of perciformes are marine shore fish, including about 2,200 species that occur in freshwater for part of their lives. Approximately 2,000 species are strictly freshwater fish, including the cichlids, bass and perch, in addition to the anabantoids.
Another common name for anabantoids is labyrinth fish, derived from the folded suprabranchial accessory breathing organ known as the labyrinth organ, called such because of its labyrinth or maze-like structure. This organ is designed to store air and extract oxygen from the air; the fish regularly rises to the surface to inhale air which passes into the labyrinth where the oxygen is absorbed into the bloodstream. Provided they remain moist, anabantoids can survive out of water for short periods by breathing air. The fish are not born with a functioning labyrinth organ, it must develop as the fish grows; fry use their gills to respirate. The size of the organ somewhat depends upon the oxygen level in the water in which the fish develop; fish native to low-oxygen water have relatively larger labyrinth organs that those inhabiting oxygen-rich waters. The fish are well adapted to this secondary breathing and would literally drown if deprived of air; the tank housing anabantoids should always be well covered to retain warmth and moisture above the water surface.
The labyrinth organ is also used by those species that build bubblenests. Air is spit out and contains an oily surface so the bubbles adhere to each other. The fertilized eggs are then spit into the bubblenest which is guarded by the male. Not all species use bubblenests; some, like the Chocolate Gourami (Sphaerichthys species), are maternal mouthbrooders; the female retains the fertilized eggs in her bucal cavity for up to 14 days as they develop and hatch. Some Betta species that occur in fast-flowing water also use mouthbrooding, but the familiar Siamese Fighting Fish Betta splendens builds a bubblenest.
Anabantoids are endemic to freshwater areas of Asia and Africa, with the vast majority of species (including those most familiar to aquarists) occurring in Asia. None are found in brackish water. Many of the larger Asian species are important food fish for the human population. The African species are generally larger and some are very predatory. The Anabantoidei, a name derived from the Greek for "to travel up" in reference to their frequent trips to the surface for air, contains three families:
The males of all species are territorial and can be aggressive to varying degrees. Some, such as the Chocolate Gourami species, have complex social structures that can only be appreciated when the fish are kept in groups in suitably-sized aquaria. Many of the species show parental care. Specifics will be included in the respective species profile.
Well-planted aquaria with minimal filtration and water movement are best. These fish spend much of their time near the surface, and floating vegetation having long root systems such as what occurs in almost all their natural habitats provides shelter and security as well as being a source of particles of food and support for bubblenests. Floating plants in the Ceratopteris genus are ideally suited to an aquarium housing these fascinating fishes. Lighting should be subdued, as these fish do not appreciate brightness; plants of the genera Cryptocoryne, Microsorium and Anubias that will thrive under less light are suitable choices beneath the canopy of floating plants. Given such a suitable environment, most species will readily spawn, and some fry will likely survive without intervention from the aquarist.
June 28, 2010
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