Can female Swordtails turn into males?

No. This is a common myth in the aquarium hobby. What actually happens is that some males are 'late developers'. They look exactly like females for the first several months of their lives before finally developing a gonopodium (modified anal fin) and the famous sword.

Do both male and female Swordtails have swords?

No, only the males grow the elongated lower tail fin. Females have a standard, fan-shaped tail fin and are generally larger and fuller-bodied than the males.

Why is my Swordtail shaking or swimming in place?

This behaviour is commonly known as 'the shimmies'. It is not a disease itself, but a symptom of severe stress, most often caused by water that is too soft or acidic, or by a sudden drop in temperature. Checking and correcting your pH and hardness usually resolves the issue.

How many Swordtails should I keep together?

They should be kept in groups of at least three, following a strict harem ratio. You should aim for one male to every two or three females. This prevents the male from harassing a single female to exhaustion and diffuses male-to-male aggression.

Do Swordtails eat their own babies?

Yes, like most livebearers, adult Swordtails exhibit no parental care and will happily eat their own fry. To save the babies, you must provide dense hiding places like Java Moss or use a separate rearing tank.

FreshwaterTropicalBeginner

Swordtail

Xiphophorus hellerii

An active and vibrantly coloured livebearer, the Swordtail is famous for the male's distinctively elongated lower tail fin.

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Ideal Conditions

Temperature: 22 – 28 °C
pH range: 7 – 8.3
Hardness: 12 – 30 dGH
Adult size: 10 – 14 cm
Standard 100L: 100 litres+
Lifespan: 3 – 5 years
Diet: Omnivore
Water flow: Moderate
Preferred setup: Spacious planted aquarium with a tight-fitting lid and ample open swimming space.

About the Swordtail

The Swordtail is an iconic freshwater species, long favoured by aquarists for its vibrant colour morphs and striking finnage. Originally from the flowing streams of Central America, this active livebearer brings constant movement to the upper and middle levels of the aquarium. The most defining feature is the male's elongated lower caudal fin, resembling a sword, which plays a key role in courtship displays. Selective breeding has produced a vast array of colours, though the wild form remains a beautiful olive green.

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Where Swordtail comes from

Native range

Central America, North America

Countries / regions

Mexico, Belize, Guatemala, Honduras

Habitat

Inhabits heavily vegetated, fast-flowing rivers, streams, and warm springs.

Widely introduced globally, often becoming an invasive species in tropical and subtropical regions outside its native range.

Similar species

Platy
Xiphophorus maculatus
Variable Platy
Xiphophorus variatus
Molly
Poecilia sphenops

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

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Platy
Xiphophorus maculatus
Shares identical water requirements and a similarly peaceful demeanour, though caution is advised as they can hybridise.
Great
Bristlenose Pleco
Ancistrus sp.
An excellent bottom-dwelling algae eater that thrives in similar community conditions without competing for space.
Great
Bronze Corydoras
Corydoras aeneus
Peaceful bottom-dwellers that help keep the substrate clean and completely ignore the top-dwelling Swordtails.
Great
Tiger Barb
Puntigrus tetrazona
Known fin-nippers that may constantly harass male Swordtails and damage their elongated caudal fins.
Compatible with caution
Siamese Fighting Fish (Male)
Betta splendens
The bright colours and flowing 'sword' of the male Swordtail may trigger a male Betta's territorial aggression.
Compatible with caution
Oscar
Astronotus ocellatus
A large, predatory cichlid that will easily swallow Swordtails whole.
Not recommended
Discus
Symphysodon aequifasciatus
Discus require very warm, soft, acidic water, which is completely incompatible with the Swordtail's need for hard, alkaline water.
Not recommended

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