Betta macrostoma Care Guide

It’s hard to forget the first time you see Betta macrostoma flare—an ember-bright fish rimmed in inky black, all drama and poise.

Known to many as the “Brunei beauty,” Betta macrostoma hails from northern Borneo, with a particularly close association to Brunei Darussalam and nearby regions. Its world is one of shaded forest streams, tea-colored leaf litter, and clear, soft waters that twist through intact rainforest. The species name says a lot: macrostoma comes from Greek for “large mouth,” and in this case the name is more than just a flourish.

Unlike the bubble-nesting bettas most people first learn about, B. macrostoma belongs to the mouthbrooding lineage. Males carry the eggs—and later the developing brood—in their mouths, a tender, high-stakes investment that turns the fish’s outsized jaws into a mobile nursery. Courtship is a quiet ballet in dim water, culminating in a careful handoff the moment the eggs are fertilized; after that, patience rules.

Visually, it’s a study in contrasts. Males show a burnished orange body with stark black edging on the fins and a dramatic dark “mask” along the lower jaw, while females keep subtler tones. When a male flares, the fins trace bold rings of black and orange that look painted on. It’s also among the larger wild bettas, and that generous head profile gives it a charismatic, almost theatrical presence.

Ecologically, B. macrostoma is an ambush-minded predator of small invertebrates, picking off insects and other tiny prey among root tangles and leaf beds. Like other Anabantoids, it carries a labyrinth organ, allowing it to gulp atmospheric air—useful in quiet backwaters where oxygen can be patchy beneath the canopy.

There’s a human story, too. For decades this fish has been a grail species among wild-betta enthusiasts, celebrated not just for its looks but for its calm, watchful demeanor and remarkable parenting. Its restricted range makes it special and vulnerable at the same time; habitat quality in northern Borneo directly shapes its future, and the species is protected in parts of its range, with collection and export tightly controlled.

If you’re drawn to fishes with personality, lineage, and a sense of place, Betta macrostoma reads like a love letter to Borneo’s forests—a living reminder that some of nature’s most striking designs are found in the quietest streams.