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Freshwater   Fishes

Least killifish
(Heterandria formosa)

Least killifish

Alternative species (click on the thumbnail to see the card)

Names

Scientific name
Heterandria formosa
Girardinus formosus
Gambusia formosa
Heterandria ommata
Hydrargyra formosa
Rivulus ommatus
Zygonectes manni

Common name
Least killifish
Dwarf topminnow
Mosqu
Midget livebearer

Origin

what are its countries of origin?

Origin: Southeastern United States
Biotope: Non specific

Dimorphism

what are the physical differences between males and females?

The male is significantly smaller than the female and has a fairly long gonopod (up to 30% of its body length).

Group

Group

Poeciliidae

Volume

what is the minimum volume for this species?

20 L / 4 Imp gal / 5 US gal

Parameters

what are the water parameters for the maintenance of this fish?

T°: 24 to 26°C or 75 to 79°F
pH: 6.5 to 7.5
Hardness: 10 to 20°dGH

Difficulty

Difficulty

Easy

Size

what is the maximum size of this fish?

Male: 2cm (0.8") - Female: 3.5cm (1.2")

Longevity

what is the average Longevity of this fish?

1 to 2 years

Living zone

in which area of the aquarium does this fish live?

Everywhere

Individuals

sociability of the species

4 (harem)

Food

How to feed the Least killifish?

Food

How to feed the Least killifish?

Its diet must essentially rely on the distribution of small live prey. Given its tiny size, artemia or cyclops nauplia as well as mosquito larvae will be perfect. For the plant part, grind spirulina. As a supplement, you can occasionally give others finely chopped flakes or powder or other commercial food.

Behavior

What kind of behavior does the Least killifish have?

Behavior

What kind of behavior does the Least killifish have?

Very peaceful and calm, even a little fearful (normal, it is systematically seen as a meal!).

Cohabitation

Who can live with the Least killifish?

Cohabitation

Who can live with the Least killifish?

The presence of many congeners is mandatory to satisfy the gregarious instinct of this fish. The base of a group is formed of one male for two to three females. Multiply this configuration as many times as your volume allows (keeping margin for reproduction). Thus, for 20 L / 4 Imp gal / 5 US gal, you can start on 2 harems of 4 fish, then for 50 L / 11 Imp gal / 13 US gal, you can start on 5 harems and so on.

Maintenance in a specific aquarium is ideal. Indeed, by being the only species in the aquarium, these fish will not suffer from the competition of larger species (which is the case of... ALL other fish species!).

However, there are some exceptions to the general rule. Indeed, cohabitation goes rather well with:
- Nannostomus (pencilfish)
- Corydoras pygmaeus (Pygmy catfish)
- Otocinclus
- Freshwater shrimp (Least killifish will eat the juveniles)

Breeding

How to breed the Least killifish?

Breeding

How to breed the Least killifish?

  • heterandria formosa mâle
  • heterandria formosa femelle

The breeding of this ovoviviparous is quite easy since it is spontaneous. To trigger spawning, the aquarium should be well lit, even sunny. The water should be slightly brackish (add a teaspoon of salt for 10 L / 2.2 Imp gal / 2.6 US gal of water). Spawning is often triggered by a good water change.

Every month, for 6 to 10 days, females give birth to 1, 2 or 3 young per day. At birth, the fry are tiny: they measure a maximum of only 5 mm (0.2"). The parents do not hunt their young, so you can safely leave them in the main aquarium.

Fry food: they find it among the surface plants at first (infusers), then they will consume the nauplia of artemia or cyclops distributed to the parents.

Its aquarium

Which aquarium for the Least killifish?

Its aquarium

Which aquarium for the Least killifish?

heterandria formosa aquarium

The presence of floating plants is essential to his well-being. Indeed, they form a secure plant cover for this small fearful fish. Generally speaking, these fish like heavily planted aquariums, which also provide them with a significant reserve of microscopic prey (infusoria). This is particularly true for the different plant mosses.

For filtration, no great power is needed because the species does not like the current. A simple corner filter with perlon and a small air pump will be perfect to maintain a correct water quality. Do not create too much surface swirl: orient the filter discharge against a wall of the tank.

Good To know

Find all additional information!

Good To know

Find all additional information!

With its maximum 2 cm (0.8"), the males of this species are among the smallest vertebrates in the animal kingdom!

In spite of its small size, this fish is quite solid and can be proposed to aquarium beginners. Indeed, it is not very sensitive to the parameters of its environment, as long as the water is warm enough.

There is an albino variety with a uniform golden coloration called Heterandria formosa Gold.

When you purchase, make sure that they have been correctly identified because confusion with Gambusias (much more aggressive) is common.

Translated with www.DeepL.com/Translator (free version)

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