About & Origin
The Full Moon (or "Halfmoon Plus"/round-tail) is a tail-shape variety of the Betta (Betta splendens), bred for a tail that opens into a very wide, almost perfectly circular fan — even fuller and rounder than the well-known halfmoon type. This blue-coloured example is native, like all bettas, to the slow-moving rice paddies, ditches, and floodplains of Thailand, Cambodia, Vietnam, and Laos.
The huge, circular tail is purely a breeding achievement rather than a wild trait, and is one of the more visually dramatic fin varieties in the hobby, showing off a solid, saturated blue colour across an unusually large fin surface.
Biologically it's identical to any other betta — the same labyrinth organ for breathing surface air, and the same territorial, solitary nature in males.
"Full Moon" describes a solid, unbroken colour pattern across the entire body and fins of Betta splendens — in this case a rich, uniform blue — as opposed to multi-coloured, marbled, or bi-colour strains.
This trade name refers to colour pattern only, not a fin type, so full moon blue bettas can appear with various tail shapes; all trace back to the same wild labyrinth fish native to Thailand's shallow rice paddies and floodplain waters.
"Full moon" describes a halfmoon-type betta whose tail spreads to a full 180 degrees or slightly beyond when flared, forming a complete half-circle silhouette — a trait selectively refined from the standard halfmoon form. The blue full moon combines this fin shape with a solid, vivid blue body and fin colouration, a colour produced by structural light-reflecting cells rather than pigment alone, which is why betta blues can shift shade with the viewing angle.
Blue full-moon bettas are consistently among the most requested colour/fin combinations in the trade.
Requirements
Keep singly, or as the sole betta in a community — never with another male betta. The oversized circular tail is heavier and more delicate than a standard betta's, so calm water with minimal current is especially important, and smooth décor helps avoid fin damage.
Avoid fin-nipping tankmates entirely given how large and vulnerable this variety's tail is.
Feeding is easy — a good quality betta pellet as a staple, with occasional live or frozen treats.
One male per tank — territorial toward other male bettas and best kept alone or with carefully chosen, peaceful, fin-safe tankmates.
A betta-specific pellet as the dietary staple, since bettas are primarily carnivorous, with occasional live or frozen bloodworm or brine shrimp for enrichment and conditioning.
A tank of at least 20 litres with a heater and gentle filtration is recommended for a genuinely healthy long-term home.
Full-moon and halfmoon tail types carry noticeably more fin surface area than standard veiltail bettas, which makes them somewhat more prone to fin damage from rough decor or strong filter flow and slightly more effortful swimmers — gentle current and soft-leaved plants or silk decor are appreciated. As always, one male per tank, housed alone.
A varied diet of quality betta pellets plus occasional live or frozen bloodworm/brine shrimp supports vivid blue colouration and good fin condition, with small regular feedings preferred over one large daily one.
A mature, cycled tank suits it far better than a freshly set-up one, and stable conditions support both long-term health and vivid, consistent colour display.
Regular partial water changes of around 25-30% weekly, combined with a reliable heater avoiding sudden swings, keep this fish healthy and its blue colouring vivid over time.
Compatibility
Water & Care Conditions
Standard betta parameters, with extra emphasis on calm water given its oversized tail:
- pH: 6.0–7.5
- Salinity / hardness: freshwater only, soft to moderately hard water
- Temperature: 24–28°C (75–82°F) — a stable heater is essential
- Light: moderate, with floating plant cover appreciated
- Oxygenation: tolerant of still, low-oxygen water via its labyrinth organ; strongly prefers calm water, as its very large tail makes swimming against current more effortful
- Fin care: the large full-moon tail is more prone to snagging or tearing on rough decor than shorter-finned varieties — smooth silk plants and driftwood are safer choices
- Flow: gentle filter current is easier on the large fin spread than strong flow
- Diet: quality betta pellets as a staple, with occasional live/frozen foods for colour and condition
- Longevity: typically lives 2-4 years, occasionally longer with excellent care
- Tank position: spends most time in the upper-to-middle water column near the surface
- Filtration: gentle flow is best, avoiding strong current that can tire the wide full-moon fin spread
As a labyrinth fish, it can breathe atmospheric air at the surface, tolerating lower dissolved oxygen and stiller water better than most community fish.
Gentle flow and smooth, snag-free decor help protect this species' fins from tearing or fatigue.
Unlike most tropical fish, this fish genuinely needs a tight-fitting lid with an air gap underneath, not to prevent jumping alone but because it periodically surfaces to gulp air through its labyrinth organ, and a fully sealed lid with no airspace can leave the air it breathes stale and humid.
A heater is essential despite the labyrinth organ's tolerance for lower oxygen -- bettas are true tropical fish and become lethargic, prone to illness, and short-lived in unheated, too-cool water, contrary to the common misconception that they can live in a small unheated bowl.