Tank Setup
- Tank size: 20 gallons minimum — swordtails are active swimmers that grow larger than most people expect (up to 5.5 inches including the sword)
- Flow: Moderate — they enjoy swimming against current
- Plants: Moderate to heavy planting. Live plants provide cover for fry.
- Lid: Essential — swordtails are excellent jumpers
Water Parameters
- Temperature: 72–82°F (22–28°C)
- pH: 7.0–8.4 (they strongly prefer alkaline water)
- GH: 12–25 dGH (hard water is ideal)
Swordtails do poorly in soft, acidic water. If your tap water is naturally soft, add crushed coral or a mineral supplement.
Breeding
Like all livebearers, swordtails breed prolifically. Females can store sperm for months and produce 20–80 fry every 28 days. If you don't want babies, keep only males — but be aware that multiple males may fight over dominance. A ratio of 1 male to 2–3 females works best.
Sex Change
Swordtails are famous for apparent sex changes — late-developing males can look like females for months before suddenly developing the sword. True female-to-male sex change is debated, but late male maturation is well documented and explains many reports of "females turning into males."
Tank Mates
Excellent community fish compatible with most peaceful species. They pair especially well with other livebearers (platies, mollies) and prefer similar water conditions. Avoid keeping with aggressive species or fin nippers.
Frequently Asked Questions
Can swordtails live with guppies?
Yes, but they may crossbreed (both are livebearers). The offspring are usually sterile and not particularly attractive. If breeding purity matters, keep them separate.