TankBud

Least killifish

Heterandria formosa

FreshwaterBrackishFish

Least killifish (Heterandria formosa)
Brian Gratwicke · CC BY 2.0

Care at a glance

Temperature
68–79°F
20–26°C
pH
6.5–7.5
Adult size
1.4 in
3.5 cm
Minimum tank
5 gal
20 L
Temperament
Peaceful
Social behavior
Social
Swim level
Middle
Difficulty
Easy
Breeding
Livebearer · Medium
Rarity
Rare
Family
Poeciliidae
Origin
United States

Overview

The least killifish is a tiny, peaceful livebearer for a small, heavily planted tank. It is easy to keep.

Did you know

A female least killifish does not drop a whole brood at once like most livebearers. She releases just one or a few fry every day or two over a stretch of time. This drawn-out delivery, called superfetation, means she carries young at different stages of development at the same time.

Caring for the least killifish

Keep least killifish in a small group in a heavily planted tank of 5 gal (20 L) or more, with gentle flow. They are tiny and tolerant, and they hang around the middle of the tank near the plants.

Keep the water calm, at 68 to 79°F (20 to 26°C) and a pH of 6.5 to 7.5. They pick at small foods all day. Feed crushed flake, micro pellets and small live or frozen foods such as daphnia and baby brine shrimp.

Least killifish are peaceful. Keep them away from large or boisterous tank mates, which might eat them.

Males stay near 2 cm, while females reach about 1.4 in (3.5 cm). Least killifish are livebearers, and females can store sperm and produce young for months from a single mating. Breeding them is of medium difficulty.

Good to know

The least killifish, Heterandria formosa, is in the family Poeciliidae, the same family as guppies and mollies. Despite the name, it is not a true killifish. It is one of the smallest fish in the world, and the species is listed as Least Concern.

In the wild

Least killifish come from the southeastern United States, in Florida, Georgia and the Carolinas. They live in warm, weedy, slow water such as swamps, ditches, ponds and quiet streams with soft bottoms and lots of plants.

Weekly picks

Tank mates

The least killifish is a peaceful, social species that keeps to the middle. These picks share a community profile with it, are safe together in both directions, and overlap on water type, temperature and pH.

Check the full mix in the stocking calculator

Common questions

What size tank does a least killifish need?

A least killifish needs at least 5 gal (20 L). It spends most of its time in the middle.

What temperature and pH does a least killifish need?

A least killifish is comfortable at 68–79°F (20–26°C) with a pH of 6.5–7.5.

What does a least killifish eat?

A least killifish picks at small foods all day. Feed it crushed flake, micro pellets and small live or frozen foods such as daphnia and baby brine shrimp.

How big does a least killifish get?

An adult least killifish reaches about 1.4 in (3.5 cm).

How can you tell a male least killifish from a female?

Males stay near 2 cm, while females reach about 1.4 in (3.5 cm).

How does a least killifish breed?

A least killifish is a livebearer. Females can store sperm and produce young for months from a single mating. Breeding it is of medium difficulty.

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