Betta Fish
It breathes air at the surface through a labyrinth organ, which is why it survives water that would not hold a tetra. Males flare rather than share a tank.
Overview
The betta is a small labyrinth fish from the Mekong basin, recorded to 6.5 cm, and it breathes air. A labyrinth organ lets it take oxygen from the surface directly, which is how it survives rice paddies and canals that would suffocate most fish, and it is also the reason it has been sold for decades in containers no other fish would tolerate.
Surviving that and doing well in it are different things. FishBase states plainly that keeping males in very small containers should be discouraged. The species is listed as Vulnerable in the wild, which sits oddly beside how common it is in shops.
Temperament
Curious, responsive to people, and genuinely aggressive towards its own kind. Males fight each other, which is what siamese fighting fish is named for, so one male lives alone.
They learn a routine quickly and will come to the front of the glass for food. A male builds a bubble nest at the surface whether or not there is a female anywhere near, and tends it. Flaring at a reflection is display rather than exercise, and a betta that spends all day at it is a betta with nothing else to look at.
Care and grooming
In the wild the diet is zooplankton, mosquito larvae and other insect larvae, so a protein rich pellet is closer to right than a flake made for community fish.
Heated and filtered, at 24 to 30 degrees C, which is 75 to 86 F. Room temperature in most houses is below that, and a cold betta is a lethargic one long before it is an ill one. Filtration should be gentle: this is a fish from standing water and a strong current pushes it around. pH anywhere from 6.0 to 8.0 is fine.
Living and exercise
Five gallons is a working minimum, heated and filtered, with a lid. Plants with soft leaves near the surface give a resting place, and the surface itself has to stay reachable because the fish has to breathe from it.
A betta can share a tank with quiet, short finned fish and with snails, and cannot share one with another male. Females can be kept together in a group, though it is a group with a pecking order rather than a peaceful shoal, and it needs space and sightlines to work.
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