Green Swordtail (Swordtail)

1. Where they come from

Green swordtails (Xiphophorus hellerii) come from Central America—Mexico down into Guatemala/Honduras—where they hang out in rivers, streams, and weedy edges. They’re used to moving water, lots of plants, and a steady buffet of algae and tiny critters.

2. Setting up their tank

Swordtails are active. They don’t just hover like guppies—they cruise. A longer tank makes them look and act way better than a tall one.

• Tank size: 20 gallons long for a small group; 29+ gallons is even nicer if you want multiple males or plan for babies
• Temp: ~72–78°F (22–26°C). They don’t need it super warm
• pH/hardness: they’re happiest in neutral-to-alkaline water with some hardness (think “livebearer water”)
• Filter: any decent filter works; moderate flow is fine and they handle current well
• Plants/cover: give them plant thickets (real or fake) and some open swimming room up front
• Lid: they jump. Yes, even the calm ones

Decor-wise, I like a “two-zone” layout: dense plants or wood on one side (breaks line-of-sight and gives females a breather), open lane on the other for their constant laps.

3. What to feed them

They’ll eat basically anything you drop in, but they color up and hold better body shape with a mix of plant-based stuff and protein. If you only feed one flake forever, they’ll still live… but they won’t look their best.

• Staple: a good quality flake or small pellet (I like one that includes spirulina/veg content)
• 2–3x per week: frozen or live foods like brine shrimp, daphnia, bloodworms (go easy on bloodworms—treat, not the main meal)
• Veg add-ons: blanched zucchini/spinach, or an algae wafer broken up
• Tiny fry foods (if you have babies): crushed flakes, baby brine shrimp, powdered fry food

4. Behavior and tankmates

They’re friendly community fish, but males can be pushy. The “sword” isn’t just for show—males posture and chase, especially in tighter tanks or if there are too many males.

• Best group: 1 male with 2–3+ females (spreads out the male attention)
• Good tankmates: other peaceful community fish that like similar water—platies, mollies, many tetras, rasboras, corydoras, bristlenose plecos
• Use caution with: long-finned slow fish (some males will nip), and very tiny shrimp (babies may get picked off)
• Avoid: aggressive/territorial fish that will harass them, or fin-nippers that will shred the sword

5. Breeding tips (if you want babies)

If you keep males and females together, you’ll probably get fry sooner or later. They’re livebearers, so females give birth to free-swimming babies. The adults will snack on fry whenever they get the chance—especially in bare tanks.

• Give fry a chance: thick floating plants (guppy grass, hornwort, water sprite) are the easiest “fry saver”
• If you want to raise numbers: move a pregnant female to a separate tank right before birth, then move her back after
• Feed heavy but keep water clean: small frequent meals for fry, plus extra water changes
• Don’t be surprised by repeat pregnancies: females can store sperm and drop multiple broods

6. Common problems to watch for

Most swordtail problems I’ve seen come down to three things: cramped tanks, dirty water, and social stress. Fix those and they’re pretty forgiving.

• Fin nipping / shredded sword: usually tankmate issues or too many males—add space, add cover, rethink tankmates
• Ich after a new fish: quarantine helps a lot; sudden temp swings can trigger it too
• Bloating/constipation: cut back, add veggie foods, try daphnia, and check you’re not overfeeding rich frozen foods
• Clamped fins / hiding: often stress (bullying) or water quality—test, water change, and watch interactions
• Stringy poop / weight loss: can be internal parasites—common in new stock; quarantine and treat if it persists
• Random deaths in “new” swordtails: some store fish are already worn down—buy active fish with full fins and good body shape