Golden Swordtail (Xiphophorus hellerii)

Start a bright, easy livebearer tank with the Golden Swordtail

The Golden Swordtail is a gold-coloured form of Xiphophorus hellerii, one of the best-known aquarium fish in the world. It is a simple, striking fish: the body is a warm yellow-gold with a net of shining scale edges, the eye is pale and bright, the dorsal and pelvic fins are clear yellow, and the tail fades to orange. In mature males the lower edge of the tail grows into a long orange-red sword, edged above and below in black, which catches the eye from across the room.

Swordtails suit keepers who want an active, robust fish that is easy to feed and will breed without special effort. They swim in open water all day, take most foods and adapt to hard tap water that would trouble many soft-water tetras. In return they need room: an adult swordtail is a substantial fish, and a group needs a long aquarium and a sensible balance of males and females.

Check the fit before you order

Browse our livebearers for sale, the swordtails category and every colour of Xiphophorus helleri we keep.

Know what you receive

One purchase quantity supplies one live Golden Swordtail in the size grade Medium. Sex is not chosen or guaranteed. The photographs show a mature male; females are larger and deeper in the body, have a fan-shaped anal fin instead of the male’s pointed gonopodium, and have no sword. Young males may not yet show the full sword, which grows as they mature.

Colour strengthens as a fish settles, so expect a paler fish straight out of the bag. Our delivery days and Live Arrival Guarantee page explains when fish travel and what to do on the day.

Choose the right number

• Three is the minimum: one male and two females, as OATA advises.
• Five or six is calmer: one or two males with the rest females spreads the attention of the males.
• Allow for fry: a group of females will soon add young, so leave space in your stocking plan.

Tell the gold swordtail forms apart

Breeders have produced many yellow, gold and orange swordtails, and their names vary between farms and shops. Seriously Fish explains that ornamental forms come from selective breeding and from crosses with the platies X. maculatus and X. variatus, and that they show colours and fin shapes never seen in the wild, olive-green fish. Golden is used for a plain yellow-gold body like the fish in our photographs; other names describe added red, orange marbling or black markings.

All these forms are one species with the same care, and they can share a tank. Mixed colours breed together, and their young often show a mixture of their parents’ colours.

Cycle the aquarium before the fish arrive

Swordtails are hardy, but OATA warns that they can be stressed by even small amounts of ammonia and nitrite. A new tank has no colony of the bacteria that break down fish waste, and adding a group of swordtails too soon leads to what OATA calls new tank syndrome: ammonia and nitrite rise, and fish fall ill. Run the filter, heater and lights for several weeks first and feed the bacteria with a fishless cycle until tests show zero ammonia and nitrite. Our guide to the aquarium nitrogen cycle explains each stage, and our first tropical tank guide lists the kit you need.

Add fish in stages

OATA advises increasing the number of fish slowly, because the bacteria need time to grow every time more fish and food are added. Add the swordtails as one group, then wait two weeks and test before adding the next group of fish.

Give a long tank and open swimming space

Swordtails are strong, fast swimmers. OATA gives an adult size of 8–12 cm, Seriously Fish a maximum of 140 mm standard length, and FishBase 14 cm for males and 16 cm for females. OATA asks for at least 80 litres for swordtails, FishBase gives a minimum tank length of 80 cm, and Seriously Fish considers a 120 × 30 cm base, about 108 litres, the smallest it would recommend.

Measure your tank with our tank volume calculator before choosing how many fish to add.

Decorate for colour and shelter

Seriously Fish suggests a heavily planted aquarium with a dark substrate, some floating plants and driftwood roots or branches to diffuse the light. A gold fish looks brightest against a dark background and deep green plants. Leave a long, open swimming lane along the front glass, and plant thickly at the back and sides so females can rest away from a persistent male.

Wild swordtails live in streams, springs, ponds and rivers from south-eastern Mexico to north-western Honduras. Seriously Fish notes that adults gather where the current is stronger and young fish in quiet margins, so a filter outlet that creates a moving area at one end and calm water at the other suits all ages.

Match the water to the fish

The sources agree that swordtails need alkaline water, pH 7.0–8.0, and a tropical temperature, but give different hardness ranges.

Check your tap water

Much of southern and eastern England has hard, alkaline tap water that suits swordtails once it is treated with a dechlorinator. Where the supply is soft, as in much of Scotland, Wales and north-west England, raise and hold hardness with a livebearer mineral salt or crushed coral in the filter, and test KH so the pH does not slide. Our water matcher compares your water with this fish.

Look after the water each week

OATA recommends a partial water change of 25% at least once a week, siphoning solid waste from the gravel, and testing ammonia, nitrite, nitrate, pH and hardness every week, especially while the tank is new and after adding fish. Treat new water with a tap water conditioner, and clean filter media only in water taken from the tank so the bacteria survive.

Weekly checklist

• Count the fish and look for any that hide or hang at the surface.
• Change 25% of the water at the same temperature.
• Test pH and KH: in soft-water areas they can drift down between changes.
• Remove surplus fry if the tank is getting crowded.

Feed little and often enough

In the wild, swordtails eat worms, crustaceans, insects and plant matter (FishBase), and Seriously Fish adds detritus and algae. OATA recommends a good flake or granule with a high algae content, plus small live or frozen foods such as Daphnia or bloodworm. Feed once a day, only what is eaten within a few minutes, because uneaten food breaks down into toxic waste.

Settle new swordtails in

Turn the aquarium lights off. Float the unopened bag for about 10 minutes so the temperature matches, then add small amounts of tank water to the bag over up to 20 minutes, as OATA describes. Net the fish into the tank and throw the bag water away. Our acclimatisation guide has photos of each step. Leave the lights off until the next day and feed a small meal then.

Watch the group over the first week. Some chasing is normal as males display, but a female that is pinned in a corner all day needs more cover or more female company.

Choose calm, robust companions

OATA describes swordtails as generally peaceful and compatible with other species, though large swordtails can be boisterous and chase timid fish. FishBase records that males are aggressive towards each other, and Seriously Fish that males in confined spaces form dominance hierarchies.

Check any mix with our tank mates checker.

Spot problems early

OATA lists the signs to watch for in any fish: unusual swimming at the surface or on the bottom, a colour much paler or darker than usual, more hiding or aggression, changed breathing, white spots or fluffy growths, missing scales or fins, weight change and poor appetite. On a gold fish, white spots and fungus stand out less than on dark fish, so look closely at the fins at feeding time.

Expect baby swordtails

Swordtails are livebearers: the male uses his gonopodium, a modified anal fin, to fertilise the female internally, and she gives birth to free-swimming young. OATA gives a pregnancy of 24–30 days and 20–80 fry; FishBase gives 20–200 young and sexual maturity at eight to twelve months. Seriously Fish notes that females can store sperm for months, so a female bought on her own may still give birth.

Adults eat fry, so thick plants and floating cover give the young a chance. To raise more, move a heavily pregnant female into a large breeding net, return her after the birth, and feed the fry crushed flake and newly hatched brine shrimp several times a day. FishBase also notes that some females change sex and become males later in life.

Plan a beginner-friendly livebearer tank

A cycled 120 cm aquarium with a group of Golden Swordtails, a few platies and a bristlenose is one of the easiest colourful set-ups for hard-water areas. Our list of the best beginner tropical fish suggests more companions, and our swordtail guide covers the species in detail.

Answer Golden Swordtail buying questions

What is a Golden Swordtail?

It is a gold-coloured, aquarium-bred form of the swordtail, Xiphophorus hellerii. Our photographs show a bright yellow-gold body with a shining scale pattern, yellow fins and, in the male, a long orange-red sword edged in black.

Is the Golden Swordtail good for beginners?

Yes, if the tank is big enough and the water is hard. Swordtails are hardy, eat almost anything and breed readily. The usual mistakes are a tank that is too small, too many males and soft, acidic water.

How big does it get?

OATA gives 8–12 cm for adult swordtails. Seriously Fish gives the species up to 140 mm standard length, and FishBase records 14 cm for males and 16 cm for females.

What size aquarium do I need?

At least 80 litres (OATA) and 80 cm long (FishBase). Seriously Fish recommends a base of 120 × 30 cm, about 108 litres, which gives a group room to swim.

What water is best?

Hard, alkaline water at 22–27°C and pH 7.0–8.0. Hardness figures differ: OATA 4–12 °dH, FishBase 9–19 and Seriously Fish 10–25 dGH. Hard tap water in much of southern and eastern England suits it once dechlorinated.

How many should I keep?

At least three, two females to each male (OATA). Males are aggressive towards each other (FishBase), so add more females rather than more males.

What do Golden Swordtails eat?

They are omnivores. Feed an algae-rich flake or granule once a day, only what is eaten in a few minutes, with small frozen or live foods such as Daphnia, brine shrimp or bloodworm a few times a week.

Why has one of my females grown a sword?

FishBase notes that swordtails can change sex from female to male under certain conditions. A female that develops a sword and a gonopodium has become a functional male; it is not a disease.

How many fish come with one purchase?

One live fish of medium size. Sex is not chosen or guaranteed; our photographs show a male, and females have no sword.

Consult the care references

• Seriously Fish: Xiphophorus hellerii — distribution and habitat, maximum size, smallest suitable tank, water values, equipment sizing, décor, wild and aquarium diet, male behaviour, sexing, sperm storage and the origin of ornamental strains.
• FishBase: Xiphophorus hellerii — male and female maximum length, water ranges, native and introduced range, wild diet, male aggression, minimum tank length, brood size, gestation, maturity and sex reversal.
• OATA: How to look after platies and swordtails — UK trade body care sheet: water values, adult size, group and sex ratio, minimum tank volume, equipment, acclimatisation, weekly care, feeding, compatibility and breeding.
• Tropical Fish Co delivery terms, beginner and swordtail guides and care articles — our own live arrival, set-up and husbandry guidance.