Swordtail
Fish
The active, sword-tailed livebearer that's basically a guppy's bigger, livelier cousin!
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🤓 Did you know? Female swordtails that have already given birth can sometimes go on to develop a sword, male coloring, and even father broods of their own later in life. Hobbyists have reported the switch for generations, and scientists have studied it since the 1930s, though researchers still debate whether it's a true sex reversal or male traits simply emerging late in a fish that was missexed as a juvenile.
🗓️ The first week
The numbers a new owner needs in the first week, each from the article it links to. Rows with no link come from the encyclopedia.
- Not two males
- The single most useful stocking rule. With two, every contest is the same pair and the loser has nowhere to be. One male with a group of females, or several males in a large planted tank where the aggression spreads.Enrichment guide →
- Tank size
- 20 gallons is the floor for a small trio; 29 to 30 gallons is the realistic starting point for an active, open-water fish. Long rather than tall, over fine gravel or sand, nothing sharp near a lyretail's fins.Setup guide →
- Water chemistry
- pH 7.0 to 8.4 in moderately hard to hard water, 12 to 30 dGH. Soft tap water gets crushed coral or a buffering product.Setup guide →
- Temperature
- 72 to 79°F is the steady target inside a workable 64 to 82°F, with swings under about 2°F in 24 hours.Setup guide →
- The lid
- They escape through gaps well under an inch. A full mesh or glass lid, a feeding hatch no larger than necessary, and a check after any rearranging.Setup guide →
- Filtration
- Flow of 4 to 5 times the tank volume an hour, from a hang-on-back or canister. A sponge filter only if fry survival is the priority.Setup guide →
- Cover
- Dense live plants along the sides and back, open water through the middle. Cover for pursued females, and broken sight lines that stop a dominant male tracking a subordinate across the tank.Enrichment guide →
- Feeding
- Once or twice a day, cleared within about 2 minutes; overfeeding is the common mistake. Vegetable content a few times a week, and bloodworms, brine shrimp or daphnia in regular rotation.Feeding guide →
- Acclimation
- Float the sealed bag 15 to 20 minutes, then drip over 45 to 60 minutes. Net the fish in; bag water carries transport ammonia.Handling guide →
- Quarantine
- 2 to 4 weeks in a separate tank before a new fish joins the display.Handling guide →
- Sexing
- Males carry the sword and a rod-like anal fin. Females have neither and are the larger sex.Handling guide →
- Sex ratio
- One male to three or four females. Chewed fins or a clamped, listless fish in a male-heavy tank means move it to a recovery tank and fix the ratio at the same time.Health guide →
- Budget
- $3 to $25 a fish, more for lyretails. Setup $115 to $190, more at 29 or 30 gallons, then $20 to $35 a month. Swordtails rarely see a vet.Cost guide →
- Lifespan
- 3 to 5 years with stable water.Cost guide →
- Adult size
- Males up to 5.5 inches (14 cm) including the sword; females up to 6.2 inches (16 cm).
- Fry are coming
- A single female produces 20 to 100 or more fry roughly every 4 weeks without a fresh mating. Swordtails and platies interbreed readily, so a mixed livebearer tank breeds hybrids.Cost guide →
- Power outage
- Oxygen is the threat, not darkness. Unplug the filter rather than letting it sit dead in the water, and keep the surface moving.Power outage guide →
- Water changes
- 25 to 30% weekly from the substrate, with conditioned water at tank temperature. Test nitrate first: under 20 ppm the routine is right, past 40 ppm the next change is 50%.Aquarium Water Changes →
🚨 Emergency card
Test the water first, then act on these today. Swordtails rarely see a vet; nearly all of this is handled at home.
- Small white spots like grains of salt across the body and fins
- Ragged, frayed, or discolored fin edges
- Buoyancy problems, usually from overfeeding or constipation
- Chewed fins or a clamped, listless fish in a male-heavy tank: move it and fix the ratio
- Scales standing out in a raised, pinecone pattern: dropsy, the hardest condition here to treat
An unbalanced male-to-female ratio measurably raises the odds of the pathogen-driven conditions above taking hold.
📰 Where to go next
How Much Does Swordtail Fish Ownership Really Cost?
$3 to $25 a fish, $115 to $190 for the tank, and why sizing up costs more than the table says.
Swordtail Tank Setup: A Real 29 to 30 Gallons and a Lid That Actually Seals
A real 29 to 30 gallons, 64 to 82F, four to five times turnover, and a lid that actually seals.
Swordtail Feeding: Schedule, Diet, and Why They Stop Eating
The two-minute rule, vegetables a few times a week, and the five reasons a swordtail goes off its food.
Swordtails Aren't Handled Either, But Ratio Is a Real Handling Decision
Float then drip, net rather than pour, quarantine two to four weeks, and sexing by the sword.
Common Swordtail Health Issues (Including the One That Isn't a Pathogen)
Ich, fin rot, dropsy and swim bladder, plus the sex ratio treated as the health issue it is.
Swordtail Enrichment: Two Males Is the Number That Causes Trouble
Why two males is the problem number, the ratio that follows from it, and what planting actually does.
🛒 What to buy
Prices and the reasoning behind each item are in How Much Does Swordtail Fish Ownership Really Cost?.
❓ Frequently Asked Questions
What size tank does a swordtail need?
20 gallons is the genuine floor for a small trio, one male and two or three females, but 29 to 30 gallons is the more realistic starting point that most direct retailers and care sheets recommend, since swordtails are more active, open-water swimmers than a molly or platy. Go long and rectangular over tall, and use a lid, swordtails are capable jumpers.
What temperature do swordtails need?
Tropical, roughly 64 to 82°F, with 72 to 79°F cited most often as the steadier target. Hold it steady rather than chasing a number: keep swings under about 2°F a day. A submersible heater is necessary unless the room stays warm all year.
Why does male-to-female ratio matter so much with swordtails?
Because males can be persistent toward females and combative toward each other. Sources commonly recommend one male to three or four females, some say two or three is enough, but the higher end spreads out mating attempts more effectively and reduces the fin damage and stress that come with a single female fielding constant attention.
📚 Encyclopedia
Swordtail
Xiphophorus hellerii
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📰 Deep Dive
🐠 How Much Does Swordtail Fish Ownership Really Cost?
🐠 Swordtails Aren't Handled Either, But Ratio Is a Real Handling Decision
🐠 Common Swordtail Health Issues (Including the One That Isn't a Pathogen)
🐠 Swordtail Tank Setup: A Real 29 to 30 Gallons and a Lid That Actually Seals
🐠 Swordtail Feeding: Schedule, Diet, and Why They Stop Eating
🐠 Swordtail Enrichment: Two Males Is the Number That Causes Trouble
🩺 Health and More
🐠 Aquarium Power Outages, Transport, and Moving Your Fish: The Complete Plan
🦠 How to Cycle a Fish Tank, Start to Finish: Fishless and Fish-In
🧽 Aquarium Filtration: How It Actually Works and How to Maintain It
🪣 Aquarium Water Changes: How Much, How Often, and What the Number Is For
🐟 Aquarium Stocking and Tankmates: How Many Fish, and Which Ones Go Together
🧪 Freshwater pH, GH, and KH: Why Chasing a Number Backfires
🤩 Fun Facts
🐠 Females Choose the Longer Sword
A male swordtail's namesake tail extension plays no role in swimming, it's pure ornament. Females show a measurable, well-documented preference for males with longer swords, and a landmark 1990 study found the strength of that preference actually increases as the gap in sword length grows, a textbook case of sexual selection through female choice.