One of the smallest fish in North America, an adult female barely reaching three centimetres and the male half that. Despite the name it is a livebearer, not a killifish at all.
Temperament
Common health issues
- Ich (white spot)
- Fin rot
- Swim bladder disorder
Care at a glance
- ExerciseLow
A calm, unhurried swimmer โ peaceful surroundings suit them best.
- GroomingRoutine tank care
Weekly partial water changes keep them in top shape.
- Living spaceNano-tank friendly
Happy in a small, stable, well-filtered tank.
- Owner experienceGreat first pet
Forgiving and easy to get started with.
- Commitment2โ3 years
Plan for a long, loving relationship.
Health to watch: Ich (white spot) ยท Fin rot ยท Swim bladder disorder
๐ Care guide
The Least Killifish (Heterandria formosa) comes from slow, weedy fresh and brackish waters of the south-eastern United States and reaches about 2 cm for males and 3 to 3.5 cm for females. Its English name is misleading: it is a poeciliid livebearer, related to guppies and mosquitofish rather than to egg-laying killifish. It practises superfetation, carrying several broods at different stages of development at once and releasing one or two fry every day or two rather than a batch at a time. A group of eight or more is happy in a 30 litre tank at 18-26C, tolerating an unheated room, in neutral to hard water at pH 7.0 to 8.2, densely planted with fine-leaved plants and gentle flow. Feed very small foods: crushed flake, micro pellets, baby brine shrimp and frozen cyclops. It is timid and slow-moving, so it must not share a tank with anything active or larger, and a species tank or a shrimp tank is the ideal home. Kept properly it breeds continuously and quietly maintains its own small population.
Frequently asked questions
How active is a Least Killifish?
Low. A calm, unhurried swimmer โ peaceful surroundings suit them best.
How much maintenance does a Least Killifish need?
Routine tank care. Weekly partial water changes keep them in top shape.
What tank size does a Least Killifish need?
Nano-tank friendly. Happy in a small, stable, well-filtered tank.
Is a Least Killifish a good fit for first-time owners?
Great first pet. Forgiving and easy to get started with.
How long do Least Killifish live?
2โ3 years. Plan for a long, loving relationship.
What health issues affect the Least Killifish?
Keep an eye out for Ich (white spot), Fin rot, Swim bladder disorder. These are worth raising with your vet, along with any screening they recommend.
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