Swordtail

Xiphophorus hellerii

Also known as: Green swordtail, Red swordtail

Water Parameters

• Temperature: 20–27°C
• pH: 7–8.2
• Hardness (GH): 143–447 ppm (8–25 dGH)

Values above are general hardness (GH). For carbonate hardness (KH), the buffer that keeps pH stable, see the water parameters guide.

Care Summary

One of the longest-established aquarium fish, named for the elongated lower tail fin the males develop. Larger and more powerfully built than guppies or platies, with the same effortless livebearing reproduction: females deliver broods of 20 to 80 free-swimming fry every four to six weeks. Available in red, green, black, and assorted hybrid strains, most of which trace back to crosses with platies. Genuinely undemanding once the water is hard and the tank is roomy enough for their constant activity, but they need that space, as an underfilled tank brings out male aggression and cramps their swimming. A good first fish for keepers with hard tap water who want more presence than a guppy. That hard water should be well buffered: a moderate to high carbonate hardness (KH) keeps the pH stable and slightly alkaline, the conditions they do best in.

Tankmates

A hardy, active livebearer that suits most peaceful community tanks. Males are territorial toward one another and spar persistently, so keep a single male, or several males in a tank large enough to break up sightlines, and always with more females than males to spread out male attention. Closely related to the platy and will interbreed with it readily, producing mixed fry. Prefers the hard, alkaline water typical of most Australian municipal supplies. Accomplished jumpers: a tight-fitting lid is essential, as swordtails are among the most common fish found dried on the floor.

Compatible with

• Platy
• Molly
• Guppy
• Bronze Corydoras
• Bristlenose Pleco
• Mystery Snail
• Nerite Snail

Avoid keeping with

• Betta
• Angelfish
• Tiger Barb
• Fin Nippers
• Large Cichlids

Common Problems

• jumping from uncovered tanks
• male-on-male aggression in cramped tanks
• overpopulation from continuous breeding
• ich
• fin rot

Sources: seriouslyfish.com, fishbase.org · Last updated: 2026-06-20