Betta

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Feeding

Strongly carnivorous in the wild, where the diet centres on small aquatic invertebrates: mosquito and midge larvae, other insect larvae, small crustaceans and zooplankton, and small worms. In captivity, betta-specific pellets are the practical staple, supplemented with frozen bloodworm or brine shrimp a few times a week. Flake is poorly suited because of the small upward-facing mouth and the species' tendency to gulp pellets at the surface. Overfeeding causes bloating quickly; small portions once or twice a day are plenty.

Compatibility

• Males cannot share a tank. The fighting response is the defining behaviour of the species and a pair of males will fight, often fatally
• Long fins attract fin-nippers (tiger barbs, serpae tetras) and the male itself will harass slow long-finned fish such as guppies, mistaking the trailing fins for those of a rival
• Most reliably kept alone. The list of suitable community tankmates is short and depends heavily on the individual fish's temperament. Calm small shoalers like ember tetras or harlequin rasboras and bottom dwellers like corydoras can work in a tank of around 75 litres or more, but expect to have a backup plan
• Female sororities (five or more in a heavily planted tank from about 40 L upward) exist as a practice, but failure is common and the welfare risk is real. Not recommended without prior experience

Origin and habitat

Native to mainland Southeast Asia, with confirmed range across Thailand, Cambodia, Laos, Myanmar, Malaysia, and Vietnam, and a likely range extending into adjacent parts of Indonesia. The species is endemic to the central plain of Thailand and was first domesticated there at least 1,000 years ago, which is one of the longest captive histories of any fish. Early selection was for fighting rather than appearance, with staged matches treated as a gambling sport; Thais still use the name pla kat (commonly glossed as 'biting fish' or 'fighter'), and modern fighter strains are sold under names such as pla kat mor. The species was carried outside Southeast Asia in the 19th century. King Rama III is reported to have given specimens to the Danish physician Theodore Cantor, and the fish reached Europe in the late 1800s before being formally described by Regan in 1910. The flowing fins and saturated colours of the ornamental forms are the product of more than a century of selective breeding from that initial fighting stock; wild Betta splendens are noticeably smaller in finnage and brownish-green to grey, with colour intensifying mainly during display. Splendens is Latin for shining. The English-language genus and common name derive from Malay; sources offer two related explanations, one tracing the name to ikan betah meaning 'enduring fish' and another to an older warrior clan name (Bettah), and the etymology is not fully settled. The species sits in the family Osphronemidae (order Anabantiformes) and has at least 72 close relatives in the same genus, although outside Southeast Asia 'betta' is used almost exclusively for this one fish. As an anabantoid, it has a labyrinth organ above the gills, a structure that lets it breathe directly from atmospheric air; that is what allows it to survive in warm, oxygen-poor habitats like rice paddies, drainage ditches, and seasonal marshes, and it is the reason the fish can live in conditions where most aquarium species would suffocate. It does not mean those conditions are good for it. The genome is unusually small for a vertebrate at around 450 megabase pairs, and a 2021 study (Wang et al., biorxiv) traced the genetic effects of centuries of domestication on the species. The fish is also Thailand's national aquatic animal, declared by the National Legislative Assembly in 2019. Despite being one of the most-kept aquarium fish in the world, wild B. splendens is listed as Vulnerable on the IUCN Red List, with pollution and habitat destruction across central Thailand as the main causes.

Breeding

Bubble-nest builder. A sexually mature male blows mucus-coated air bubbles at the surface into a floating raft, usually anchored against a piece of floating plant or tank wall. When a gravid female (rounded with eggs and showing vertical bars) is introduced, the male alternates between displaying and adding to the nest. Spawning happens beneath the nest in the characteristic anabantoid embrace: the male wraps his body around the female, who releases eggs in batches of around ten to forty at a time while he simultaneously fertilises them. The eggs sink, and the male darts after them, collecting each one in his mouth and spitting it into the bubble raft above. The cycle repeats over several hours, and a single spawning typically yields on the order of a hundred to several hundred eggs, occasionally more. Once spawning ends the male turns on the female and drives her off, so she has to be removed or she will be killed. The male then guards the nest alone, repairing it, catching any eggs that fall, and removing infertile ones. Hatching takes roughly 24 to 48 hours. The fry hang vertically from the nest for a couple of days while absorbing their yolk sacs, then swim horizontally and the male's job is essentially done; remove him at that point. First food is infusoria, paramecium, or fine commercial fry food, moving to baby brine shrimp as the fry grow. Males in a single brood start to become aggressive with each other at about two months and need to be separated into individual jars or compartmentalised grow-out by then.

Common problems

Fin rot is the most common health complaint, generally a bacterial infection that takes hold when fins are damaged in poor water quality. Long-finned strains are particularly prone because the heavy fins are easy to tear and slow to heal. The first response is water-quality correction; an antibacterial only goes in if the fins keep degrading after that. Velvet disease, caused by the dinoflagellate parasite Piscinoodinium, shows up as a fine gold or rust-coloured dust over the body and is well documented in this species, with fry especially vulnerable. Temperature stability matters: the fish is tropical, not room-temperature, and drifting temperatures suppress the immune system and predispose fish to all of the above. A stable heated tank around 25 to 27 C is the basic requirement. The biggest welfare problem is housing. The species is routinely sold and kept in small, unfurnished jars and cups, which a peer-reviewed welfare study (Clark-Shen et al. 2024) describes as the default in the trade despite the impact on the animal; the labyrinth organ keeps the fish alive in those containers, but unheated bowls truncate lifespan to months rather than the multi-year span a properly housed betta can reach. Mirrors and other bettas in line of sight cause continuous flaring and chronic stress, so avoid both. Males cannot be cohabited under any circumstances. Females in sororities (groups of five or more in a heavily planted larger tank) are occasionally kept together, but the practice is contested in the hobby and has a high failure rate; it is not a beginner setup.

Bioload

Further reading

• Why your angelfish ate your neons
• Blackwater tanks: replicating acidic jungle streams
• Fish that recognize their owners