Species · Aquatic pet

Siamese Fighting Fish

Betta splendens

Labyrinth fish of Thai rice paddies, bred for centuries first for fighting and then for fins, and sold today in cups it was never meant to stay in.

The betta is the most personable fish most people will ever keep — it recognises its keeper, begs at the glass, builds bubble nests and watches the room like a tiny opinionated dragon. It is also the most systematically mistreated fish in retail: the cup it is sold from gets mistaken for a housing recommendation. A betta needs what every tropical fish needs — heat, a filter, a cycled tank of twenty litres or more — plus one rule all its own: one male, one tank, no exceptions, because the fighting in the name is not decorative.

At a glance

Lifespan: 3–5 years
Adult size: 6–7 cm
Minimum tank: 20 L+, heated, filtered, lidded — they jump
Water: Tropical fresh, warm and still
Weekly upkeep: Weekly partial water change
Diet: Betta pellets, tiny portions; they beg convincingly
Company: One male, alone, always
With children: Watch, don’t touch — a genuinely engaging first fish
Tankmates: Usually none; anything flashy or nippy ends badly

Varieties · 4 listed

Veiltail to halfmoon to plakat — fin fashion on the same fish. The longest fins are heaviest to carry; the short-finned plakat is closest to the animal Thailand actually bred.

Veiltail
Halfmoon
Plakat
Koi

Right for you if

You want one fish with genuine personality in a modest, well-run tank.
Heater, filter and lid are already in the budget — the cup stops at the shop.
A pet that interacts through the glass appeals to the household.
You accept the solitude rule without wanting to test it.

Wrong for you if

The vase, the bowl or the desk cup was the plan.
You want a community centrepiece; this is a solo artist.
Unheated rooms and no heater — a betta in cold water is a fish shutting down.
Two males “to see what happens”. What happens is the name.

Welfare and sourcing — read this part

The cup is survivable retail, not housing: most of what goes wrong for fish follows stress, poor water quality and overcrowding,¹ and a cup is all three in 300 millilitres. The twenty-litre heated tank is not deluxe betta keeping; it is minimum fish keeping.
Cycle the tank before the fish: the bacteria that make water safe take four to six weeks to establish,² and the classic betta story — cup to brand-new tank to dead in a month — is new tank syndrome wearing a bow.
Buy the alert one: flaring, patrolling, building bubbles. A listless betta in a shop cup may be cold rather than sick — but you cannot tell from the outside, and you are not running a rescue.

Sources

Disorders and Diseases of Fish. MSD Veterinary Manual 2026. Accessed 2026-09-05. International MSD Veterinary Manual Many of the disorders and diseases that occur in fish are the result of stress, poor water quality, overcrowding, and failure to quarantine. New tank syndrome is ammonia accumulating when fish are added before the biological filter works, typically in the first one to three weeks. Ich (white spot) is a common protozoal infestation whose fast reproduction is what makes it deadly.
Providing a Home for Fish. MSD Veterinary Manual 2026. Accessed 2026-09-05. International MSD Veterinary Manual Prolonged ammonia exposure is highly toxic to fish; bacteria convert ammonia to nitrite (also toxic) and then to nitrate, and those bacterial colonies take four to six weeks to establish on their own. Stock gradually so the colonies grow with the waste.

Every source here was checked, not recalled. Where this page makes a health statement and no source appears against it, that is not an oversight we have hidden — it means the claim is not yet sourced, and the build reports how many are in that state.

Availability, registration and keeping requirements differ from place to place. Check the rules where you live before you commit to any animal — we describe animals, not law.