TankBud

Variety of Green swordtail

Koi swordtail

Xiphophorus hellerii

One of 6 varieties of Xiphophorus hellerii · See all varieties →

Also known as Sanke Koi Swordtail

FreshwaterFish

Koi swordtail (Xiphophorus hellerii)

Varieties · Xiphophorus hellerii

See all 6 →

Care at a glance

Temperature
68–82°F
20–28°C
pH
7.0–8.0
Adult size
5.9 in
15 cm
Minimum tank
20 gal
76 L
Temperament
Peaceful
Social behavior
Social
Swim level
Middle
Difficulty
Beginner
Breeding
Livebearer · Easy
Rarity
Very common
Family
Poeciliidae

Overview

The koi swordtail carries red and white blocks on a pale body. It is a peaceful beginner fish for the middle of a community tank.

Did you know

The koi swordtail's names are borrowed wholesale from Japanese pond koi. Kohaku, also sold as Santa Claus, is red on white, and sanke or tricolor adds black on top. Neither term says anything about the fish's genetics, only about how the blocks happen to fall.

Caring for the koi swordtail

Koi swordtails are active swimmers that cruise the middle of the tank and appreciate length. Give them at least 20 gal (76 L), with planted edges, open space in the middle and moderate flow. The blocks are never identical between fish, so pick individuals rather than ordering by name.

Keep them in hard, alkaline water at 68 to 82°F (20 to 28°C) and a pH of 7.0 to 8.0. They are easy eaters that take quality flake or pellet. Add some vegetable matter and the odd frozen treat.

Koi swordtails are peaceful and social, and they are safe in a community tank. Keep a small group with more females than males to spread out the males' attention. Males carry a long sword extension on the lower tail fin. Females are larger bodied but lack the sword.

They are livebearers, giving birth to live young rather than laying eggs. Females can store sperm and produce several broods from one mating. They breed readily, so expect fry and give the babies plants to hide in. Breeding them is easy.

Good to know

The koi swordtail is a form of Xiphophorus hellerii, in the family Poeciliidae. Its white is unpigmented skin rather than a white pigment, so the pattern is really red patches over a pale ground. Retailers describe the sanke as a white or silver fish with reddish-orange patches plus black blotches and spots. Block placement is not fixed by any single gene, and spawns range from nearly all white to mostly red. Nothing about the pattern breeds true block for block.

In the wild

The koi swordtail is farm stock, much of it bred in Asia. No breeder or year is documented for the original koi line, so its origin is unclear. Wild green swordtails carry no blocked red and white.

Weekly picks

Tank mates

The koi swordtail is a 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

Is a koi swordtail a different species from the green swordtail?

No. A koi swordtail is a variety of the green swordtail, Xiphophorus hellerii, and it wants the same tank, water and food as the species.

What size tank does a koi swordtail need?

A koi swordtail needs at least 20 gal (76 L). It spends most of its time in the middle.

What does a koi swordtail eat?

A koi swordtail eats quality flake or pellet foods. Give it some vegetable matter and the odd frozen treat as well.

How big does a koi swordtail get?

An adult koi swordtail reaches about 5.9 in (15 cm).

How can you tell a male koi swordtail from a female?

Males have a long sword that extends from the lower tail fin. Females are bigger in the body and have no sword.

How does a koi swordtail breed?

A koi swordtail bears live young instead of laying eggs. A female can store sperm, so one mating gives several broods. Breeding is easy, and the fry need plants for cover.

Related species