Freshwater Fish

Swordtail

Xiphophorus hellerii

Active livebearer with a bladed tailBeginner

Lifespan: 3-5 years
Size: 4-5.5 in
Social needs: Social; keep 6+ together
Time: 15 min daily; weekly water change
Cost: Medium
Diet: Omnivore (flake, pellet, veg, live foods)

Overview

What is this animal?

Swordtails are lively livebearers from Central America, named for the long blade extending from the lower tail of mature males.
Closely related to platies, they are larger, more active, and need more swimming room than their compact cousins.

Hardy and adaptable, they come in red, green, pineapple, and tuxedo varieties.
They are strong swimmers and accomplished jumpers, so they suit keepers who provide length, a secure lid, and stable, slightly hard water.

Temperament

Swordtails are active and largely peaceful, but mature males can be territorial toward each other, sparring over space and females.
Six is a good starting group, ideally one male with five females; keeping a single male, or several with plenty of room and a female-biased group, reduces conflict and stress.

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They are confident, outgoing community fish that occupy open water and rarely hide.
As ready breeders, mixed groups produce frequent fry, which adults will eat unless dense planting offers the young somewhere to shelter.

A good fit for

Larger community aquariums with swimming space
Beginners wanting an active, hardy fish
Hard-water planted setups
Keepers who can provide a secure lid

Common mistakes to avoid

Undersized tanks restricting active swimmers
Multiple males fighting in tight quarters
Open tanks letting these jumpers escape
Low-fibre diets causing constipation

Enclosure

Minimum 30 gallons, for a group of 6

Cannot be kept alone. The minimum is 6, and the space above is for that group.

Their size and energy call for a tank with a footprint of at least 48 x 12 in and at least 30 US gallons of water, kept at 72-82°F in hard, alkaline water and filtered to keep nitrate low.
A standard 29- or 30-gallon tank is only 30-36 in long, so shop for length: open swimming space matters more than height for these powerful swimmers.

A tight-fitting lid is essential, as swordtails are notorious jumpers.
Provide planting at the sides and back for cover and fry refuge while leaving the central water column clear for their constant activity.

Check your enclosure

Supplies

Setup

Tank and stand
Filter
Heater and thermometer
Substrate, plants and decor
Liquid test kit
Dechlorinator and starter supplies

Ongoing

Quality tropical flake or micro-pellet
Spirulina or vegetable flake
Frozen brine shrimp and daphnia
Frozen or freeze-dried bloodworm
Veg clip for courgette and spinach

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Baby brine shrimp hatchery or frozen equivalent for fry
Fine net for removing leftovers

Safe substrate: Fine, smooth sand · Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras) · Bare bottom (quarantine and grow-out only)

Work out the cost

Care routine

Daily

Check temperature and equipment
Feed
Head-count and look everyone over

Every few days

Top up evaporationevery 3 days

Weekly

Test the water
Water change and gravel vacuum
Wipe the front glass only

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Every few weeks

Trim and thin the plantsevery 2 weeks

Monthly

Check supplies and reagent dates
Replace or recharge chemical media, if you use any (skip it in a blackwater tank)
Review the fry plan
Rinse the filter media

Health review: Quarterly stocking and health review, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended size What will it cost?Setup, monthly and over its whole life, itemised Is this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Omnivore (flake, pellet, veg, live foods)

Swordtails are omnivores that do best on a varied, vegetable-inclusive diet.
Use a quality flake or pellet base, add spirulina, algae, and blanched greens, and offer frozen or live foods such as bloodworms, daphnia, and brine shrimp several times a week.

Feed modest amounts once or twice daily, only what is consumed quickly.
Like other livebearers they tend to overeat and can become constipated on a low-fibre diet, so keep vegetable matter a regular part of the menu.

Health

Signs of good health, and the common problems

Swordtails are robust given clean, hard, stable water, but suffer ich, fin rot, and constipation under neglect or poor diet.
Steady warmth, strong filtration, and weekly water changes prevent most disease in this hardy species.

Mass-bred stock can be genetically weaker, so source carefully and quarantine new fish.
Watch for clamped fins, white spots, or a swollen belly with stringy faeces: white spot (ich) and internal parasites need prompt treatment, while constipation from a low-fibre diet usually responds to corrected feeding.

Is this urgent?

6 warning signs and how fast to act, 3 of them right away

In a fish tank the patient is usually the water. Test before you treat: dosing a healthy tank for a disease it does not have makes things worse.

Go now

Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.

Now

Fish gasping at the surface with fast gill movement, or crowding the filter outflowIncrease surface movement now (gently in a betta or gourami tank, without creating a strong current), then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems. Bettas, gouramis and corydoras rise to gulp air as part of normal breathing; the warning is constant gulping, fast gill movement, or the whole group hanging at the top.

Now

Sudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths usually point at the water or the equipment rather than a pathogen, so rule those out first.

Now

Today

Flashing: repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.

Today

White salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.

Today

Soon

Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.

A few days

Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.

This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it, and the time to find one is before you need one.

Bedding and substrate

3 safe, 4 with a caveat, 2 to avoid

Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.

Safe

Fine, smooth sandCorrect for corydoras, kuhli loaches, eartheaters such as rams and acaras, and anything else that sifts or burrows. Barbels wear away on sharp gravel.

safe

Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras)Rinse thoroughly before use. Grain size should be too large to swallow and too small to trap food. Kuhli loaches need sand to burrow into and rams and acaras sift mouthfuls of it; bronze and panda corydoras manage on smooth fine gravel, but sterbai corydoras need sand.

safe

Bare bottom (quarantine and grow-out only)Legitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration, and it is no long-term home for burrowing loaches or sand-sifters.

safe

With a caveat

Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.

with a caveat

Aquasoil for planted tanksExcellent for plants, but most active soils soften the water and pull pH and KH down for months, and many leach ammonia for the first weeks. Right for soft-water species; wrong for hard-water animals (livebearers, rainbowfish, goldfish, and snails, whose shells erode in soft, acidic water) unless you test GH and KH and remineralise. Cycle around it; do not stock into it.

with a caveat

Very deep sand bedsAnaerobic pockets form below about 2 inches in still sand. Either keep it shallow or keep it stirred.

with a caveat

Painted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.

with a caveat

Never

Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.

never

Anything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.

never

This is our general list for freshwater fish. We have not built one specific to Swordtail yet.

Top resources for more info

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