All fish / Poeciliidae

Northern Swordtail

Xiphophorus nigrensis

Also known as el abra swordtail, rio choy swordtail, panuco swordtail, nigrensis swordtail, x. nigrensis, 北方剑尾鱼

A small wild swordtail from clear, fast, limestone streams in eastern Mexico. Males have bluish iridescent flanks, a dark lateral stripe and a short black-edged sword, and come in distinct large courting and small sneaking forms. It is kept by livebearer enthusiasts who want to maintain pure wild strains and is a well-known study species for sexual selection research.

Care at a glance

Care level

Moderate

Temperament

Peaceful

Adult size

4.5 cm

Temperature

20 to 26 °C

pH

7 to 8

Smallest tank

60 litres

Keep as

Group with more females than males, e.g. 1 male to 2 or 3 females

Diet

Omnivore: quality flakes, small pellets, live or frozen bloodworm, daphnia and brine shrimp, plus algae and vegetable matter

Swims

Middle of the tank

Lifespan

2 to 4 years

Water

Freshwater

Wild range

Río Choy and Río Coy basins (Pánuco system), San Luis Potosí, Mexico

Breeding

A livebearer; females give birth to small broods of fully formed fry every four weeks or so after internal fertilisation. Breeding is straightforward in a well-planted tank with cover, though adults may eat fry and broods are smaller than in domestic swordtails.

Good to know

Do not mix with other swordtails or platies, as it hybridises readily and pure wild lines are valued. Likes clean, well-oxygenated, cooler hard water with some current.