Siamese fighting fish

The galaxy koi betta is a selectively bred colour strain of Betta splendens, the Siamese fighting fish, a labyrinth fish from the warm, slow waters of Southeast Asia. The galaxy koi name describes its marbled, multi-coloured pattern: flecks of metallic blue, red, and white scattered over a darker body, with the marble gene causing that pattern to shift and spread over the fish's life. Like every betta, it gulps air at the surface through a labyrinth organ, an adaptation to the oxygen-poor ditches, rice paddies, and floodplains its wild ancestors live in.

Males are highly territorial and will flare at and attack other males, so only one male belongs in a tank. They are carnivores, taking insect larvae, small crustaceans, and zooplankton in the wild, and quality betta pellets, frozen bloodworm, daphnia, and brine shrimp in the aquarium. A single male can head a peaceful community of small, non-nippy fish, but avoid fin-nippers such as tiger barbs and other gouramis, and treat dwarf shrimp as possible snacks rather than safe tankmates.

Despite the old reputation as a bowl fish, a betta does best in a heated, gently filtered tank of at least 15 litres around 24 to 30 degrees Celsius, in soft to moderately hard water that is slightly acidic to neutral. Bettas are bubble-nest breeders: a conditioned male blows a raft of bubbles at the surface, courts a female beneath it, wraps around her to fertilise the eggs, then guards the nest alone and returns any eggs that fall. This only happens with deliberate pairing, so a lone display male never produces fry, and the colours you buy are the work of breeders rather than something your tank will repeat by accident.