Description
The betta is by far the best-known aquarium fish in the world. It is also the worst kept. It is worth understanding why, because the reason is a specific misunderstanding rather than bad faith.
The betta has an organ called the labyrinth, a heavily vascularised structure that lets it breathe atmospheric air at the surface. It is an adaptation to the warm, oxygen-poor waters where it lives. That real detail became a sales pitch: since it can breathe air, it gets displayed in tiny jars and vases with no filter and no heater.
That it survives in a jar does not mean it should live in one. The labyrinth solves oxygen — not ammonia, not temperature, not swimming space. A betta in a vase does not suffocate: it is slowly poisoned and spends its life cold.
Give it a real 25 litres with a heater and gentle filtration and you will see a different animal: curious, active, one that recognises whoever approaches the glass and spreads fins that more than justify its fame. It is one of the few fish with which you get something close to a personal relationship.
Behavior
Males are incompatible with each other, without exception. They fight until one dies or is crippled, which is where the name fighting fish comes from. No tank is large enough and no amount of hiding places helps: you do not keep two males together, full stop.
With everything else it is more nuanced than usually told. The betta is not aggressive towards everything — it is territorial and short-fused with whatever it reads as a rival:
- Long fins and bright colours — male guppies, gouramis — get mistaken for another betta and attacked.
- Fast, tireless swimmers such as danios stress it even without touching it.
- Fin nippers like tiger barbs shred its fins, which then take weeks to regrow.
It coexists reasonably with corydoras, otocinclus, kuhli loaches and calm rasboras: fish from a different zone, discreet and without showy fins. Even so it depends on the individual, and you need a plan B in case yours will not tolerate it.
On females and sorority tanks: widely seen on social media, works in few cases and ends badly in many. It requires a large group, a big tank, extremely dense planting and constant supervision, and even then it can collapse overnight. If you are starting out, this is not the way.
A practical note: it needs its own hiding places and free access to the surface. And watch the flow: a powerful filter in a small tank exhausts it, because those fins were not built for swimming against a current.
Habitat
Betta splendens comes from rice paddies, shallow pools and canals in Thailand and Cambodia: warm, still, shallow, densely vegetated water that in the dry season shrinks to puddles with very little dissolved oxygen.
That origin explains almost everything it needs at once:
- It breathes air because its pool runs out of oxygen. Never seal the surface completely or block its way up.
- It cannot cope with strong flow: it comes from still water. If the filter moves a lot, diffuse the outlet or reduce the rate.
- It needs real warmth, between 24 and 28 degrees. At room temperature in a temperate flat it spends half the year cold, its immune system drops and it falls ill. This is the silent cause of half the bettas that die early.
Reproducing its environment is easy: broad-leaved plants to rest on, something floating, a piece of wood or a cave, and dim light. It does not need an expensive setup, it needs the right one.
Habitats
Details
🌊 Water parameters
🐠 Minimum tank size
Breeding
It is one of the most extraordinary behaviours you can watch in a home aquarium. The male builds a bubble nest at the surface, each bubble coated in saliva so it does not burst, often beneath a floating leaf that acts as a roof.
When the female accepts, the nuptial embrace follows: the male wraps his body around her and turns her over, and the eggs fall as he fertilises them. He then collects them one by one in his mouth and places them in the nest.
From then on the male takes sole charge: repairing the nest, returning fallen eggs and going without food for days. The female must be removed as soon as spawning ends, because he attacks her without hesitation to protect the brood.
An honest warning: breeding bettas is easy to start and hard to finish well. One spawn yields hundreds of fry, and as soon as the young males define themselves they must be separated one by one. Many people jump in without anywhere to put them afterwards. Think it through beforehand, not halfway.
Diet
The betta is carnivorous, which sets it apart from almost every other community fish. In the wild it eats insects, larvae and small invertebrates; no algae and no plant matter.
- Staple: betta-specific pellets with animal protein as the first ingredient. Ordinary tropical flake is a poor choice: too much plant filler.
- Supplement: mosquito larvae, brine shrimp or daphnia, frozen or live, two or three times a week.
- Fasting: one day a week without food does it good and prevents digestive trouble.
Here is the commonest mistake after the vase: overfeeding. The betta always begs, no matter how much you give it. Its stomach is roughly the size of its eye, and two or three pellets a day are enough.
Excess causes constipation and bloating, which in turn presses on the swim bladder and leaves the fish swimming sideways or unable to descend. If it happens, fast it for two or three days and then offer a blanched, peeled pea. It almost always resolves that way — and it could almost always have been avoided by feeding less.
What about your tank?
Enter your tank's values to see only the compatible species that fit them. Litres apply to fish.
Compatible fish
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 6–7.5 and 24–27 °C.
They share water: pH 6–7 and 24–28 °C.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 6–7.5 and 24–25 °C.
They share water: pH 6.5–7.5 and 24 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6.5–7.5 and 24–28 °C.
They share water: pH 6–7.5 and 25–28 °C.
They share water: pH 6–7.5 and 24–28 °C.
They share water: pH 7.5 and 24–28 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7.5 and 24–28 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6–7 and 24–26 °C.
They share water: pH 6.5–7.2 and 24–26 °C.
They share water: pH 6–7.5 and 24–26 °C.
They share water: pH 7–7.5 and 24–27 °C.
They share water: pH 6–7 and 26–28 °C.
They share water: pH 6–7 and 24–26 °C.
They share water: pH 6.5–7.5 and 24–26 °C.
They share water: pH 6–6.5 and 24–28 °C.
They share water: pH 6–7.5 and 24–28 °C.
They share water: pH 6–7.5 and 24–27 °C.
They share water: pH 7–7.5 and 24–28 °C.
Compatible invertebrates
General guidance based on water parameters, behaviour and known exceptions; always review the individual animals' and aquarium's specific needs.
They share water: pH 7–7.5 and 24–28 °C.
They share water: pH 6–6.5 and 24 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 7–7.5 and 24–25 °C.
They share water: pH 7.5 and 24–28 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6–6.8 and 24 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6–6.8 and 24 °C. They only meet at the very edge, so the tank has to hold that value.
They share water: pH 6.5–7.5 and 24–27 °C.
They share water: pH 7–7.5 and 24–28 °C.
They share water: pH 7–7.5 and 24–28 °C.
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They share water: pH 7–7.5 and 24–28 °C.
Sources
- FishBaseFroese, R. and D. Pauly. Editors. 2026. FishBase. World Wide Web electronic publication.
- Seriously FishSeriously Fish. Betta splendens. Ficha de especie; consultada 2026-08.
Both sources stretch the pH up to 8 and the temperature up to 30 °C. The profile keeps a narrower range on purpose.
Plan your next aquarium
Is this fish right for you? Plan a suitable aquarium before setting it up.