Montezuma swordtail

Care at a glance

Overview

Keep them as a small colony of about six to eight in a tank of 120 liters or more, with females outnumbering the males. Run the water at 20 to 26 C, and aim for the cooler end of that since they do best in well oxygenated, subtropical leaning conditions with clean water. They are mostly peaceful and a little shy, swimming in the middle of the tank, though males get competitive with each other, so keep just one male per group or a larger group with several females. They have low tolerance for nitrate, so use strong filtration and do generous weekly water changes. Feed flakes or pellets with frozen treats like daphnia or bloodworms, and keep tankmates similarly sized, peaceful, and happy in hard water. Avoid fin nippers and very small fish. They breed readily and adults will eat the fry, so give dense planting or cover for survivors. Never release unwanted fish or fry into local waterways, and check your local rules before keeping or rehoming them.

In the wild

Montezuma swordtails come from the Rio Panuco basin in northeastern Mexico, across San Luis Potosi, Tamaulipas, and Veracruz, where they live in hard, alkaline springs and flowing streams. To match that, give them a tank of at least 120 liters with sand or fine substrate, plants around the edges, and plenty of open water down the middle. Keep the water hard and on the alkaline side, around pH 7 to 8, with good flow and steady oxygen since they come from cooler, well moving water.

Good to know

This is a livebearer in the family Poeciliidae. The body runs about 6 to 7.5 cm, but a mature male grows an unusually long horizontal sword off the tail that roughly doubles his total length to around 12 to 14 cm. That sword is why they need more swimming room than the common swordtail, Xiphophorus hellerii. Females give birth to live, fully formed fry rather than laying eggs.

Did you know

The long sword is mostly a male display feature, used to attract females and to signal to rival males, which is part of why males posture and compete with one another. Females have no sword at all, so the difference between the sexes is easy to spot once the males mature.

Related species

• 

  Northern mountain swordtail

  Xiphophorus nezahualcoyotl

  3.5 in (9 cm)29 gal (110 L)68–79°F (20–26°C)

• 

  Green swordtail

  Xiphophorus hellerii

  5.9 in (15 cm)24 gal (90 L)68–82°F (20–28°C)

• 

  Sheepshead swordtail

  Xiphophorus birchmanni

  2.8 in (7 cm)24 gal (90 L)68–81°F (20–27°C)

• 

  Pygmy swordtail

  Xiphophorus pygmaeus

  1.6 in (4 cm)11 gal (40 L)75–82°F (24–28°C)

• 

  Southern platy

  Xiphophorus maculatus

  2.8 in (7 cm)15 gal (55 L)68–79°F (20–26°C)

• 

  Variable platy

  Xiphophorus variatus

  2.8 in (7 cm)15 gal (55 L)68–79°F (20–26°C)