Betta pi

A member of the Betta waseri group, clay-yellow fish in which mature males usually have iridescent gold scales on the gill cover and black throat markings. A large fish from peat swamps in southern Thailand, Kelantan and Terengganu, named for a dark throat marking shaped like the Greek letter pi.

Wild bettas are hard to identify, and fish in the trade are often mislabelled. Ask for the collecting locality, and keep populations separate to avoid crossing them.

Males are usually more colourful, with more-extended fins and a broader head, and they tend to grow larger than females.

Use dim light, dried leaf litter, wood and floating plants, with only the gentlest filtration. A sponge filter works well. Add small caves such as clay pots or lengths of pipe, and use a tight lid, because the warm, humid air above the water protects the labyrinth organ. There is no need to use peat, which is unsustainable. Leaf litter does the same job.

Calm for a betta, and spends much of its time in shade. It becomes bolder in a dim, well-planted tank.

A pair or small group is the usual choice. A compatible pair is best formed from a group, because random pairs do not always get along, and the weaker fish may be killed.

Less aggressive than many bubble nesters, but pairs can still fight when space is short.

Not for a standard community tank. Keep it alone or with very peaceful fish that like the same water, such as some small rasboras and loaches, because bigger or more vigorous fish will intimidate and outcompete it. Do not mix it with long-finned fish, or with fin nippers. Small shrimp may be eaten.

Soft, acidic blackwater from peat swamp forest. Few minerals, and pH in the wild can fall below 4.

A small predator of insects and other invertebrates. Offer plenty of small live or frozen foods for colour and condition.

Bettas seem especially prone to obesity, so feed small portions. Mouthbrooding males do not eat while holding eggs.

A paternal mouthbrooder. After a long courtship the pair spawn in an embrace, and the female passes the eggs to the male, who holds them in his mouth for about 9 to 16 days before releasing free-swimming fry. Stressed or inexperienced males may swallow the eggs early, so use a separate quiet tank, and leave the female and any other fish where they are. Fit the tightest lid you can, because the fry need warm, humid air to develop their labyrinth organ.