Betta macrostoma Care Guide - Setup, Diet & Breeding

Betta macrostoma is one of the largest and most striking wild bettas kept in aquariums. Its name means “large mouth”, reflecting the broad head and substantial mouth that give the species a powerful, unmistakable profile. Mature males typically show rich red-orange colouration across the body and fins, contrasted with dark markings and pale edging, while females are generally more subdued.

This species is a relatively secretive but intelligent fish that spends much of its time exploring cover and watching its surroundings. Males can be strongly territorial, especially when defending a breeding site, and both sexes may display with spread fins and changes in body colour when challenged.

In nature, Betta macrostoma lives in quiet, shaded waters beneath dense rainforest vegetation. Leaf litter, submerged roots and overhanging plants break up the habitat and provide shelter, while tannins from decaying leaves can give the water a tea-coloured appearance.

Unlike bubble-nesting bettas such as Betta splendens, Betta macrostoma carries its eggs in the male’s mouth. This unusual reproductive strategy, combined with its restricted natural range and spectacular adult appearance, has made it a particularly sought-after wild betta among specialist aquarists.

Betta macrostoma is native to northern Borneo, occurring in Brunei and the Malaysian state of Sarawak. It inhabits forest streams, small pools and peat-influenced blackwater habitats associated with the upper reaches of the Brunei River system and nearby watersheds.

A pair should have at least 75 litres, with a footprint of approximately 60 by 30 cm; a larger aquarium is preferable for a group or community arrangement. Use a secure lid, gentle filtration and subdued lighting. The layout should include dense planting, driftwood, smooth branches, caves and broad leaves that create secluded territories and shaded resting places. A dark sand or fine-gravel substrate, leaf litter and botanicals help recreate its forest-stream environment. Water movement should be gentle, with ample surface cover and no strong current through the main shelter areas.

Adults can reach around 10–12 cm (4–4.7 inches) in total length. Males are usually larger and heavier-bodied than females, although individual size varies.

Betta macrostoma is primarily a carnivore and does best on a varied diet of meaty foods. Offer appropriately sized frozen or live foods such as bloodworm, blackworm, daphnia, brine shrimp, mosquito larvae and small earthworms. High-quality soft pellets formulated for carnivorous bettas can be used as part of the diet, but variety is important. Feed modest portions and remove uneaten food promptly, as this species can be sensitive to deteriorating water quality.

Betta macrostoma is best kept as a dedicated species, pair or carefully managed group because males can be territorial and the fish may become stressed by boisterous tankmates. In a sufficiently spacious, mature blackwater aquarium, possible companions include peaceful, small rasboras such as harlequin rasboras or chili rasboras, along with other calm fish that tolerate warm, soft, acidic water. Avoid fin-nipping species, highly active community fish, large predators and other territorial anabantoids. Multiple males should not be housed together unless the aquarium is exceptionally large and heavily structured with visual barriers.

Betta macrostoma is a paternal mouthbrooder. Provide a quiet, dimly lit breeding aquarium with soft, acidic water, cover and several hiding places. After spawning, the male collects the eggs and holds them in his mouth for around 10 to 14 days, depending on temperature. The female may help guard the territory, but should be removed if she becomes disruptive. Once released, the fry can be offered tiny live foods such as freshly hatched baby brine shrimp and microworms. A male may swallow a brood, particularly if disturbed, so minimise activity around the aquarium during incubation.

Males are generally larger, more robust and much more colourful, often displaying vivid red-orange areas, stronger dark markings and more elongated fins. Females are usually smaller with a rounder body and predominantly brown, tan or muted reddish colouration, though mature females can also show attractive patterning.