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Knife livebearer

Alfaro cultratus

FreshwaterFish

Knife livebearer (Alfaro cultratus)
Haplochromis · CC BY-SA 3.0

Care at a glance

Temperature
75–82°F
24–28°C
pH
6.5–7.5
Adult size
3 in
7.6 cm
Minimum tank
32 gal
120 L
Temperament
Mostly peaceful
Social behavior
Social
Swim level
Middle
Difficulty
Difficult
Breeding
Medium
Rarity
Rare
Family
Poeciliidae
Origin
Costa Rica, Nicaragua, Panama

Overview

The knife livebearer is a slim, silvery fish that lives in the middle and upper water and does best in a group. It is mostly peaceful toward other species, but males squabble among themselves, so keep it either as a small single-species group with room to spread out or alongside calm, similar-sized fish. It can be shy and is a little demanding about clean water, so give it steady filtration and gentle current. Feed a varied mix of flake, frozen and live foods. It likes soft to medium, near-neutral water. A tank of 120 liters or larger gives a group the space it needs.

In the wild

Alfaro cultratus comes from the warm lowland streams and rivers of Costa Rica, Nicaragua and Panama, where it lives in flowing, well-oxygenated water. Keep it between 24 and 28 C with a pH from about 6.5 to 7.5 and soft to moderately hard water. A planted tank with clear swimming lanes, gentle to moderate flow and very clean water recreates its home. Stable conditions and good oxygen keep this slightly sensitive fish comfortable.

Good to know

The knife livebearer belongs to the family Poeciliidae and grows to around 7 to 8 cm. It is named for a keel of enlarged, overlapping scales along the lower edge of the tail, which gives the body a sharp, knife-like underside. Males carry a gonopodium and long, extended pelvic fins, and they fertilize females internally so that the larger, fuller females give birth to live young. Breeding is possible at home but takes some care, earning it a moderate rating.

Did you know

Studies have found that knife livebearers from streams full of predators grow slimmer, more knife-edged bodies than those from safer waters, a shape that helps them dart away from danger.

Weekly picks

Tank mates

Knife livebearer is a mostly 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 Knife livebearer need?

A Knife livebearer needs at least 32 gal (120 L). It spends most of its time in the middle.

What temperature and pH does a Knife livebearer need?

A Knife livebearer is comfortable at 75–82°F (24–28°C) with a pH of 6.5–7.5.

How big does a Knife livebearer get?

An adult Knife livebearer reaches about 3 in (7.6 cm).

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