Least killifish

Heterandria formosa

FreshwaterBrackishFish

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: Medium
Rarity: Rare
Origin: United States
Family: Poeciliidae

Overview

These are peaceful, easy little fish best kept in a small group among plants. They hang around the mid water near vegetation and pick at small foods all day. Feed crushed flake, micro-pellets, and small live or frozen foods like daphnia and baby brine shrimp. Keep them in temps from the low to mid 20s C with calm water and no large or boisterous tankmates that might eat them.

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. A heavily planted tank with gentle flow copies that closely. They are tiny and tolerant, so even a 20 liter setup with dense planting suits a small group.

Good to know

Heterandria formosa is in the family Poeciliidae, the same family as guppies and mollies, so despite the name it is not a true killifish. It is one of the smallest fish in the world, with females around 3.5 cm and males near 2 cm. It is a livebearer, and females can store sperm and produce young for months from a single mating. The species is listed as Least Concern.

Did you know

Instead of dropping a whole brood at once like most livebearers, a female least killifish 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.