TankBud

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
Livebearer · Medium
Rarity
Rare
Family
Poeciliidae
Origin
Costa Rica, Nicaragua, Panama

Overview

The knife livebearer is a slim, silvery livebearer for a calm, planted tank. It is a fish for experienced keepers.

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. That shape helps them dart away from danger.

Caring for the knife livebearer

Knife livebearers do best in a group. A tank of 32 gal (120 L) or larger gives a group the space it needs. A planted tank with clear swimming lanes suits them, and they spend most of their time in the middle.

Knife livebearers are a little demanding about clean water. Keep it very clean and stable, soft to moderately hard, at 75 to 82°F (24 to 28°C) and a pH of 6.5 to 7.5. Steady filtration, a gentle to moderate flow and good oxygen keep this slightly sensitive fish comfortable.

Feed a varied mix of flake, frozen and live foods. Knife livebearers can be shy, and they are mostly peaceful toward other species. Males squabble among themselves, so give a small single-species group room to spread out. Calm, similar-sized fish suit them as tank mates.

Males carry a gonopodium and long, extended pelvic fins, while females are larger and fuller. Males fertilize the females internally, and the females give birth to live young. Breeding is possible at home but takes some care.

Good to know

The knife livebearer, Alfaro cultratus, belongs to the family Poeciliidae. It is named for a keel of enlarged, overlapping scales along the lower edge of the tail. That keel gives the body a sharp, knife-like underside.

In the wild

The knife livebearer comes from the warm lowland streams and rivers of Costa Rica, Nicaragua and Panama. There it lives in flowing, well-oxygenated water.

Weekly picks

Tank mates

The 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.

What does a knife livebearer eat?

A knife livebearer eats a varied mix of flake, frozen and live foods.

How big does a knife livebearer get?

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

How can you tell a male knife livebearer from a female?

Males carry a gonopodium and long, extended pelvic fins. Females are larger and fuller.

How does a knife livebearer breed?

A knife livebearer gives birth to live young after the male fertilizes the female internally. Breeding is possible at home but takes some care.

Related species