All fish / Poeciliidae

Knife Livebearer

Alfaro cultratus

Also known as knife-edged livebearer, alfaro livebearer, orange-tailed knife livebearer, アルファロ・クルトラタス

A slim, laterally compressed livebearer with a sharp keel of scales along the underside of the tail base, which gives it the knife name. Its body is a translucent silvery olive with a bluish sheen, and the fins are often yellowish to orange. Hobbyists keep it as an unusual, active Central American stream fish for a well-planted community or biotope tank.

Care at a glance

Care level

Moderate

Temperament

Semi

Adult size

7 cm

Temperature

24 to 28 °C

pH

7 to 8

Smallest tank

100 litres

Keep as

Group of 6 or more, with more females than males

Diet

Omnivore: live and frozen insect larvae, brine shrimp, daphnia, flake and small pellets

Swims

Top of the tank

Lifespan

2 to 4 years

Water

Freshwater

Wild range

Atlantic and Pacific slopes of Nicaragua, Costa Rica and Panama

Breeding

Fertilisation is internal: males pass sperm using a gonopodium, and females give birth to well-formed young after about four weeks. Adults readily eat their fry, so breeding is easier with dense plants or a separate rearing tank. It is not prolific compared with guppies or mollies.

Good to know

Can be skittish and will jump, so use a tight lid. Males may squabble and nip, and the fish does best in clean, well-oxygenated water with some current.