Least Killifish care guide
Least Killifish (Heterandria formosa) — minimum tank 20 L, temperature 20-26 °C, pH 6.5-8.
Compiled by Aquairi from published sources · Published · Updated
Overview
The Least Killifish (Heterandria formosa) is among the smallest freshwater fish in North America. Despite its common name it is a poeciliid livebearer, not a true killifish, and is native to the south-eastern United States.
Taxonomy
- Family: Poeciliidae
- Genus: Heterandria
- Scientific name: Heterandria formosa
- Common synonyms: Dwarf Livebearer
Habitat
Inhabits densely vegetated swamps, marshes and slow streams from North Carolina south to Florida and west into Louisiana, in soft to moderately hard, slightly alkaline water.
Tank requirements
- Minimum tank volume: 20 L (5.3 US gal)
- Adult size: 1.5-3 cm
- Temperature: 20-26 °C (68-79 °F)
- pH: 6.5-8
- GH: 8-20 °dGH
- Water flow: none
- Lifespan: 2-3 years
Diet
A micro-omnivore. Offer crushed flakes, micro-pellets and small live or frozen foods (daphnia, cyclops, baby brine shrimp).
Compatibility
A peaceful nano fish. Keep in a heavily planted small aquarium, either as a species-only setup or with other tiny peaceful species such as Boraras rasboras and dwarf shrimp.
Breeding
A livebearer with unusual reproductive biology: females give birth to a small number of fry every few days over an extended period (a strategy known as superfetation).
Least Killifish Breeding Guide (Heterandria formosa)
Overview
The Least Killifish (Heterandria formosa) is one of the smallest fish in the world and, like most poeciliids, is a livebearer. It is notable for releasing its young gradually rather than in a single brood, occupying vegetated, slow-moving or still freshwater (and sometimes brackish) habitats.
Sexing
Males possess the gonopodium, a modified anal fin used for internal fertilization, which females lack. Males grow to about 2 cm while females are a little larger at about 3 cm; females also show distinctive dark spots on the dorsal and anal fins.
Conditioning
This species breeds readily in vegetated freshwater. Avoid pairing close relatives: even a single generation of full-sibling mating reduces male reproductive success and offspring viability and delays maturation.
Breeding Setup
Provide a densely planted tank that mimics its natural vegetated, slow or standing water. Dense plants give the gradually released fry cover.
Spawning Behavior & Trigger
Fertilization is internal via the male's gonopodium. Rather than dropping a single large brood, the female delivers her young in a staggered fashion.
Birth & Fry Care
As many as 40 fry are released over a 10-14 day period, occasionally longer, rather than all at once. The tiny fry can be reared in the same densely planted tank, taking very small live and powdered foods suited to their size.
Common Challenges
The fry and adults are extremely small, so foods must be correspondingly fine, and inbreeding should be avoided to maintain vigour.