A “halfmoon”, a “koi plakat” or a “crowntail” is not a species — it is a selectively bred variety of the wild Betta splendens. The atlas treats those as one story, told here, rather than as separate accounts. For the wild fish, see Betta splendens and its relatives in the splendens group.
From fighting fish to ornamental fish
The fighting fish was domesticated in Thailand (then Siam) centuries ago, originally for the contests that give the genus its English name rather than for its looks. Villagers collected wild Betta splendens from rice paddies and ditches and bred the most combative fish; the long-finned, intensely coloured ornamental forms came later, as the fish reached Western aquarists in the nineteenth and twentieth centuries and breeders began selecting for finnage and colour instead of aggression. A century of that selection has produced an animal that looks dramatically unlike its wild ancestor — and that, in the most extreme show forms, can barely swim against its own fins.
Finnage types
Breeders name strains first by the shape and spread of the fins. The common groups include the veiltail (the long, drooping tail of the classic pet-shop betta), the halfmoon (a caudal fin that opens to a full 180° half-circle), the delta and super delta (triangular tails approaching the halfmoon), the crowntail and combtail (rays extending past the fin webbing in a spiky fringe), the double tail (a caudal split into two lobes), the plakat (a short-finned form closest to the wild fighter, now hugely popular), and the elaborate rosetail and feathertail (extreme branching that often crosses into deformity).
Colour types
On top of finnage, strains are described by colour and pattern: solids (red, blue, black “melano”, white, yellow, orange), iridescent steel, royal and turquoise blues and greens, metallic copper and gold, and patterned forms — the multicoloured koi and marble (a mobile pattern caused by a transposon that can shift over a fish’s life), the pale-bodied dragon with its thick metallic scaling, the butterfly with banded fins, and the dark-faced mustard gas bicolours. New trade names appear constantly; they describe appearance, not lineage.
How the fancy fish differs from the wild fish
The wild Betta splendens is a short-finned, brown-and-iridescent paddy fish that flares red and blue only when displaying. The aquarium strains are larger-finned, far more colourful, generally less hardy, and — through generations of tank breeding — adapted to warm, still, often harder water than the soft, seasonally variable habitat of the wild population. The exaggerated finnage of show forms can impair swimming and is prone to tearing and infection, and the most heavily inbred lines carry health problems. None of this applies to the wild species accounts elsewhere in this atlas, which describe fish as they occur in nature.
A note on welfare and the cup
The pet-trade image of a betta in a tiny cup or bowl reflects how the fish are shipped and displayed, not what they need. Like their wild relatives, domesticated bettas breathe air through a labyrinth organ and can survive poor water for a time — but surviving is not thriving. They do best in a heated, filtered, planted aquarium of adequate volume, the same warm, quiet, structure-rich conditions that suit the wild species this atlas profiles.