Green Swordtail

Where they come from (and why they act the way they do)

Green swordtails (Xiphophorus hellerii) come from Central America—think Mexico down into Honduras—where they live in rivers, streams, and weedy edges of faster water. That “river fish” background shows up in the aquarium: they love swimming room, appreciate clean water, and they’re always out and about.

Setting up their tank

If you want swordtails to look good and stop bickering as much, give them space. They’re active, mid-water swimmers, and a cramped tank turns them into little gremlins.

• Tank size: 20 gallons long for a small group is a comfortable starting point. Bigger is always easier with swordtails.
• Temp: ~72–78°F (22–26°C). They don’t need super warm water.
• pH/Hardness: they handle a range, but they’re happiest in neutral to slightly alkaline, moderately hard water.
• Filtration: steady filtration and regular water changes go a long way—these are hearty fish, but they’re not fans of dirty water.
• Flow: moderate flow is fine. They’ll play in it if you give them a current.
• Layout: open swimming space in the middle, plants around the edges (real or fake), and a few visual breaks like driftwood or rock piles.

A lid helps. Swordtails aren’t the worst jumpers, but an excited chase can end with one on the floor. I learned that one the annoying way.

What to feed them

Swordtails will eat basically anything you’ll put in the tank, but they look best (and the females hold up better through pregnancy) when you mix in some veggie-heavy foods.

• Daily staple: a good flake or small pellet (I like one with some spirulina or plant matter in it).
• 2–4x per week: frozen or live foods like brine shrimp, daphnia, or bloodworms (treat, not the whole diet).
• Veggie boosts: blanched zucchini/spinach, or an algae wafer now and then.
• Feeding rhythm: small portions 1–2 times a day—enough that it’s gone in a couple minutes.

Behavior and tankmates

They’re busy, social fish with a mild “pecking order” vibe. Males will posture and chase, and one male in a small tank can harass everyone. In a roomy tank with the right ratios, they settle down and just look great cruising around.

• Best group setup: 1 male with 2–3+ females, or a bigger group with lots of space and cover.
• Good tankmates: other peaceful community fish that like similar water—platies, mollies, larger tetras, rasboras, danios, Corydoras, bristlenose plecos.
• Use caution with: fancy guppies (fin nipping can happen), slow long-finned fish (they may get picked at), and very timid species that hate activity.
• Avoid: aggressive cichlids and anything that sees a swordtail as a snack.

Breeding tips (because they probably will)

Swordtails are livebearers, so yes—if you have males and females together, you’ll get babies. Females can also store sperm, so a “female-only” tank can still surprise you for a while after you remove the male.

• How to tell sexes: males have a gonopodium (modified anal fin) and often a longer “sword.” Females are rounder with a fan-shaped anal fin.
• Gestation: roughly 4–6 weeks depending on temperature and the female’s condition.
• Fry survival: in a community tank, many fry get eaten (which keeps numbers manageable). If you want to raise them, give dense plants like guppy grass, hornwort, or floating cover.
• Fry food: crushed flake, baby brine shrimp, and powdered fry foods work well.

Common problems to watch for

They’re beginner-friendly, but swordtails still throw you a few classic livebearer headaches. Most issues I’ve seen come down to stress from crowding, sloppy water, or a diet that’s all protein and no greens.

• Male harassment: females hiding, torn fins, constant chasing—fix with more space, more females per male, and more cover.
• Ich/white spot after a new fish: quarantine new arrivals if you can, and don’t trust “it looked fine at the store.”
• Fin nipping: usually tankmate-related or too many males; watch for ragged tails and split fins.
• Bloat/constipation: common with heavy feeding and dry-only diets—add veggie foods and offer daphnia.
• Shimmying or hanging at the surface: can be water quality, oxygen, or stress—check ammonia/nitrite, bump aeration, do a water change.