Swordtail Fish Care Guide: Colours, Breeding and Tank Setup

The swordtail (Xiphophorus hellerii) is one of the most recognisable freshwater fish in the hobby, instantly identifiable by the striking sword-shaped extension on the male’s tail fin. These robust livebearers combine bold colours, active personalities and straightforward care requirements into a package that appeals to beginners and experienced aquarists alike.

What many newcomers do not realise is that swordtails are bigger and more active than their livebearer cousins the guppy and the platy. They need more tank space than you might expect, and they have a well-deserved reputation as escape artists. This guide covers everything you need to keep swordtails successfully in Singapore’s tropical conditions.

The Iconic Sword

The swordtail’s namesake feature is the elongated lower ray of the male’s caudal (tail) fin, which extends into a pointed “sword.” This sword can add 3-4 cm to the fish’s overall length and is edged in black, creating a striking visual contrast against the body colour. Only males develop the sword, making sexing adult fish effortless.

The sword serves no practical swimming purpose — it is a sexual selection trait. Females preferentially mate with males bearing longer, more symmetrical swords. Some varieties, such as the lyretail swordtail, have been selectively bred to extend both the upper and lower tail rays, creating a forked appearance. While visually impressive, lyretail males are less effective breeders as the modification can interfere with mating.

Colour Varieties

Selective breeding has produced a spectacular range of swordtail colours and patterns.

Wild-type swordtails are subtly attractive with olive-green bodies and a red lateral stripe. They are hardier than most fancy varieties and make an excellent choice for aquarists who value natural aesthetics.

Tank Size and Setup

This is where many beginners go wrong with swordtails. Despite being sold as small juveniles in shops, adult swordtails reach 10-12 cm (males) to 12-14 cm (females, excluding sword), making them considerably larger than guppies or platys.

More importantly, swordtails are powerful, active swimmers that cruise constantly. They need space to move.

• Minimum tank size: 75 litres (60 cm long) for a small group
• Recommended: 120 litres (80-90 cm long) for a proper community
• Ideal: 150+ litres for mixed livebearer communities

Tank length matters more than height for swordtails. A long, shallow tank is preferable to a tall, narrow one. Provide a mix of open swimming areas and planted sections for cover. Hardy plants like Java fern, Vallisneria and Amazon swords work well — swordtails are not plant-eaters but may uproot delicate stem plants with their active swimming.

Need help designing a tank for swordtails? Our custom aquarium service can create the perfect setup for your space.

Water Parameters

Swordtails are adaptable fish that prefer moderately hard, slightly alkaline water — a near-perfect match for Singapore tap water.

Singapore’s warm climate means swordtails may experience temperatures at the upper end of their comfort zone. During the hottest months (April to June), use a clip-on fan or ensure adequate surface agitation to improve oxygenation. Swordtails are active fish with a higher oxygen demand than more sedentary species.

Always treat tap water with a conditioner that neutralises chloramine before adding it to the tank. PUB uses chloramine rather than free chlorine, and it does not gas off simply by leaving water standing overnight.

Feeding

Swordtails are omnivores with a healthy appetite. Like platys, they have a herbivorous inclination and benefit from vegetable matter in their diet.

• Staple: Quality flake or pellet food with spirulina or vegetable content
• Vegetables: Blanched zucchini, cucumber, shelled peas and spinach
• Protein: Frozen bloodworms, brine shrimp and daphnia as treats (two to three times weekly)
• Algae: Swordtails naturally graze on algae, which supplements their diet

Feed once or twice daily in amounts consumed within two to three minutes. Swordtails are greedy feeders that will eat until they are visibly bloated if given the chance. Overfeeding leads to obesity, reduced lifespan and poor water quality.

Breeding and Sex Ratios

As livebearers, swordtails give birth to fully formed, free-swimming fry. A healthy female produces 20-80 fry every four to six weeks. Breeding is effortless — the challenge, as with all livebearers, is managing the resulting population.

Critical: Sex Ratios

Maintaining the correct sex ratio is more important with swordtails than with smaller livebearers. Male swordtails are persistent breeders and can be genuinely aggressive towards females, chasing them relentlessly. Keep a minimum ratio of one male to three females. In smaller tanks, keeping just one male with several females prevents male-on-male aggression, which can be surprisingly intense — dominant males may bully subordinate males to death.

Sex Change

Swordtails exhibit a fascinating phenomenon: mature females can develop male characteristics, including the sword extension. This is not a true sex change in most cases but rather late-developing male traits in fish that initially appeared female. These late-changing fish are usually infertile as males. Regardless, it can be startling to see a “female” suddenly sprout a sword — but it is entirely normal swordtail behaviour.

Raising Fry

Swordtail fry are relatively large at birth and can eat crushed flake food immediately. Dense plant cover — especially floating plants like water sprite — dramatically increases survival rates. In a well-planted community tank, some fry will inevitably survive even without intervention, helping to maintain a self-sustaining population.

Tank Mates

Swordtails are generally peaceful community fish, though males can be pushy with each other and occasionally with other fish. Good tank mates include:

• Platys and mollies — fellow livebearers with similar requirements
• Larger tetras (rummy-nose, Congo tetras) — big enough not to be bullied
• Corydoras catfish — peaceful bottom-dwellers
• Bristlenose plecos — excellent algae control for swordtail-sized tanks
• Rainbowfish — active, similarly sized and non-aggressive
• Peaceful gouramis (pearl, honey) — complement swordtails well

Avoid very small fish like neon tetras in tight quarters, as large swordtails may harass them. Aggressive cichlids are also poor choices. Do not house swordtails with guppies in breeding setups, as male swordtails may harass female guppies.

Jumping Risk and Prevention

This deserves its own section because it catches many swordtail keepers off-guard. Swordtails are accomplished jumpers. They can clear the water surface by several centimetres, and a startled swordtail can easily leap out of an open-top tank.

You absolutely need a lid or cover on your swordtail tank. This is not optional. Common triggers for jumping include:

• Sudden disturbances (knocking the tank, switching on lights in a dark room)
• Male aggression — a harassed fish may jump to escape
• Poor water quality
• Overcrowding

If you prefer an open-top aquascape for aesthetic reasons, lower the water level by at least 8-10 cm from the rim. However, a glass or mesh lid is the safest option. In Singapore’s humid climate, glass lids also reduce evaporation — a practical benefit.

Health and Diseases

Swordtails are hardy when kept in appropriate conditions. Common health issues include:

White Spot Disease (Ich)

Appears as tiny white dots on the body. Treat with commercial ich medication. Singapore’s warm water actually helps by accelerating the parasite’s life cycle, making treatment faster.

Fin Rot

Bacterial infection causing fraying or deterioration of fins. Almost always linked to poor water quality. Improve conditions with water changes; use antibacterial medication for severe cases.

Swim Bladder Disorder

Fish swims erratically, floats at the surface or sinks to the bottom. Often caused by overfeeding or constipation. Fast the fish for 24-48 hours, then offer a shelled, blanched pea.

Columnaris

Bacterial infection causing white cotton-like patches. Thrives in warm water and spreads quickly. Treat promptly with antibacterial medication and quarantine affected fish. Maintaining good water quality is the best prevention.

Frequently Asked Questions

How big do swordtails get?

Males reach 10-12 cm including the sword extension, while females grow to 12-14 cm. This makes swordtails substantially larger than guppies (3-6 cm) or platys (5-7 cm). Plan your tank size accordingly — juveniles in the shop will double or triple in size within a few months.

Can I keep just one swordtail?

Swordtails are social fish and do best in groups. A single swordtail will survive but may be stressed or reclusive. If space is limited, a group of three to four females (without a male) works well. If keeping a male, always include at least three females to distribute his attention.

Why is my male swordtail chasing everyone?

Male swordtails can be assertive, especially during breeding. If a male constantly harasses other fish, the usual cause is an inadequate female-to-male ratio or insufficient tank space. Ensure you have at least three females per male and provide enough space (120 litres minimum for a group). Adding plants and decorations that break line of sight can also reduce aggression.

Do swordtails need a heater in Singapore?

No. Singapore’s ambient temperature keeps aquarium water at 28-32°C, which swordtails tolerate well. In fact, during the hottest periods, you may need to cool the water slightly with a fan rather than heat it. A heater is only necessary if the tank is in a heavily air-conditioned room that regularly drops below 22°C.

Swordtails are a classic choice that rewards good care with vibrant colour and active behaviour. If you are looking for quality swordtail stock or need advice on setting up the right tank, visit Gensou’s shop at 5 Everton Park or reach out via our contact page. Our team has been helping Singapore aquarists choose and care for fish for over two decades.