Halfmoon Betta

Looks how to spot one

Fins and scales

The halfmoon betta has a large, flowing caudal fin that spreads a full 180 degrees, forming a clean D or half-circle shape when fully flared. The dorsal and anal fins are also extended and flowing. The body is compact and streamlined, typical of Betta splendens, but the heavy finnage makes the fish appear larger than it is.63

Personality what they are like

Males are highly territorial and aggressive towards other males, and will fight to the death if housed together. They are generally peaceful towards non-threatening tankmates that do not resemble them, but their heavy fins make them slow and clumsy, so they can be easily bullied by fast or nippy fish. They are alert, curious and interactive with their owners, often patrolling their territory and resting on leaves.452

Daily activity how busy a day looks

Halfmoon bettas are not high-endurance swimmers. They need a tank with open swimming space plus resting areas near the surface and lower down. Gentle water flow is essential, as strong current will push them around. They enjoy exploring plants and decor, and benefit from broad-leaved plants like Anubias to rest on near the surface.54

Grooming and care the hands-on bits

The large fins are prone to damage and infection, so the tank must have no sharp or rough decor. Water quality must be pristine, with warm temperatures around 27°C (81°F). Regular water changes and gentle filtration are essential to prevent fin rot. Avoid strong water flow and provide smooth, broad-leaved plants for resting.42

Home where they are happiest

A minimum tank size of 20-30 litres (5-8 gallons) for a single specimen, though 10 gallons (about 38 litres) is recommended for more space. The water should be warm (24-30°C), with a pH of 6-8 and soft to moderately hard water. The tank must have gentle filtration, no strong current, and plenty of resting spots near the surface. Broad-leaved plants and smooth decor are ideal. The species is not venomous and not protected, but it is a domesticated variety that does not exist in the wild.427

Food basics what goes in the bowl

Obligate carnivore. Feed high-protein betta pellets or flakes, supplemented with frozen or live foods such as bloodworms, brine shrimp and daphnia. Feed small amounts once or twice a day, only as much as the fish can consume in about 30 seconds. Avoid overfeeding, as they are prone to bloating and constipation.483

Company who they like around

Males must be kept alone, as they will fight other males to the death. Females can sometimes be kept in groups (sororities) but this is advanced and requires a large, heavily planted tank. A male and female should not be kept together permanently. The halfmoon's slow swimming makes it vulnerable to fin-nipping by fast or aggressive tankmates; only peaceful, slow-moving species like nerite snails are safe cohabitants.42

The story where it all began

The halfmoon betta is a selectively bred variety of the Siamese fighting fish, Betta splendens. It was developed in the 1980s by European and Thai breeders working from earlier 'delta' lines, which had caudal fins spreading to about 90 degrees. Through decades of selective pairing for ever-wider spread, breeders achieved the modern 180-degree halfmoon tail. The trait was codified in IBC show standards in the 1990s. The halfmoon does not exist in the wild; it is purely a product of artificial selection, and no wild Betta splendens has ever displayed a true halfmoon caudal fin.34

Recognised by the official bits

IBC (International Betta Congress)

Show standards codified the halfmoon trait in the 1990s, requiring a 180-degree caudal spread.3