Photo: Photo made by User:Sebastian Wallroth (Public domain) — via Wikimedia Commons
Swordtail (Xiphophorus hellerii)
A sleek, active livebearer whose dazzling sword tail and endless colour varieties make it one of the most recognisable fish in the freshwater hobby.
Will it live with a Swordtail?
We compare each fish against your swordtail on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.
- Agassiz's Corydoras✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Agassiz's Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Banjo Catfish✅ CompatiblePeaceful · 15 cm · Medium care · 20–26 °C (68–79 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Blood Red Tiger Pleco✅ CompatiblePeaceful · 6 cm · Medium care · 24–29 °C (75–84 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Bolivian Ram✅ CompatiblePeaceful · 8 cm · Medium care · 24–28 °C (75–82 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 24–28 °C — no size, zone or temperament conflicts.
- Burmese Loach✅ CompatiblePeaceful · 9 cm · Easy care · 22–28 °C (72–82 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Corydoras Catfish✅ CompatiblePeaceful · 6.5 cm · Easy care · 22–26 °C (72–79 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–26 °C — no size, zone or temperament conflicts.
- Keep Corydoras Catfish in a shoal of 6+ or it gets stressed and nippy.
- Elegant Cory✅ CompatiblePeaceful · 6 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Elegant Cory in a shoal of 6+ or it gets stressed and nippy.
- False Julii Corydoras✅ CompatiblePeaceful · 6 cm · Easy care · 22–26 °C (72–79 °F)
- Compatible on the things that matter: shared water near 22–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep False Julii Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Leopard Frog Pleco✅ CompatiblePeaceful · 9 cm · Medium care · 25–30 °C (77–86 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Peppered Corydoras✅ CompatiblePeaceful · 7 cm · Easy care · 18–26 °C (64–79 °F)
- Compatible on the things that matter: shared water near 22–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Peppered Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Slate Corydoras✅ CompatiblePeaceful · 6 cm · Medium care · 23–28 °C (73–82 °F)
- Compatible on the things that matter: shared water near 23–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Slate Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Spotfin Corydoras✅ CompatiblePeaceful · 6.5 cm · Easy care · 22–26 °C (72–79 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–26 °C — no size, zone or temperament conflicts.
- Keep Spotfin Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Spotted Corydoras✅ CompatiblePeaceful · 7 cm · Easy care · 22–27 °C (72–81 °F)
- Semi-aggressive + Peaceful, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Spotted Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Spotted Rubbernose Pleco✅ CompatiblePeaceful · 12 cm · Medium care · 20–26 °C (68–79 °F)
- Semi-aggressive + Peaceful, but with no direct clash here, and their water overlaps around 22–26 °C — no size, zone or temperament conflicts.
- Sterbai Corydoras✅ CompatiblePeaceful · 6.5 cm · Medium care · 24–30 °C (75–86 °F)
- Compatible on the things that matter: shared water near 24–28 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Sterbai Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Angelfish⚠️ With cautionSemi-aggressive · 15 cm · Medium care · 24–30 °C (75–86 °F)
- Water hardness preferences differ (Swordtail 12–25 vs Angelfish 3–10 dGH).
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 75 L tank is below the ~110 L this pairing really wants — crowding raises aggression.
- Blue Flash Cichlid⚠️ With cautionSemi-aggressive · 15 cm · Medium care · 24–28 °C (75–82 °F)
- Swordtail and Blue Flash Cichlid can both be territorial; doable with space and dense planting, but watch for chasing.
- Your 75 L tank is below the ~210 L this pairing really wants — crowding raises aggression.
- Calvus Cichlid⚠️ With cautionSemi-aggressive · 14 cm · Medium care · 24–27 °C (75–81 °F)
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 75 L tank is below the ~120 L this pairing really wants — crowding raises aggression.
- Clown Barb⚠️ With cautionSemi-aggressive · 15 cm · Medium care · 24–30 °C (75–86 °F)
- Different pH ranges (7–8.3 vs 6–6.5); doable if you sit in the shared band, but not ideal long-term.
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 75 L tank is below the ~132 L this pairing really wants — crowding raises aggression.
- Keep Clown Barb in a shoal of 6+ or it gets stressed and nippy.
- Denison Barb⚠️ With cautionPeaceful · 15 cm · Medium care · 18–25 °C (64–77 °F)
- Your 75 L tank is below the ~200 L this pairing really wants — crowding raises aggression.
- Keep Denison Barb in a shoal of 6+ or it gets stressed and nippy.
- Dolphin Cichlid⚠️ With cautionSemi-aggressive · 15 cm · Medium care · 23–28 °C (73–82 °F)
- Water hardness preferences differ (Swordtail 12–25 vs Dolphin Cichlid 2–10 dGH).
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 75 L tank is below the ~208 L this pairing really wants — crowding raises aggression.
- Eureka Red Peacock Cichlid⚠️ With cautionSemi-aggressive · 15 cm · Medium care · 24–28 °C (75–82 °F)
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 75 L tank is below the ~200 L this pairing really wants — crowding raises aggression.
- Firemouth Cichlid⚠️ With cautionSemi-aggressive · 15 cm · Medium care · 22–29 °C (72–84 °F)
- Swordtail and Firemouth Cichlid can both be territorial; doable with space and dense planting, but watch for chasing.
- Your 75 L tank is below the ~200 L this pairing really wants — crowding raises aggression.
- Giant Glass Catfish⚠️ With cautionPeaceful · 15 cm · Medium care · 22–27 °C (72–81 °F)
- Your 75 L tank is below the ~120 L this pairing really wants — crowding raises aggression.
- Gold Zebra Loach⚠️ With cautionSemi-aggressive · 15 cm · Medium care · 25–29 °C (77–84 °F)
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 75 L tank is below the ~130 L this pairing really wants — crowding raises aggression.
- Green Phantom Pleco⚠️ With cautionSemi-aggressive · 15 cm · Medium care · 26–30 °C (79–86 °F)
- Water hardness preferences differ (Swordtail 12–25 vs Green Phantom Pleco 1–10 dGH).
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 75 L tank is below the ~150 L this pairing really wants — crowding raises aggression.
- Marbled Hoplo⚠️ With cautionPeaceful · 14 cm · Easy care · 22–28 °C (72–82 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Moonlight Gourami⚠️ With cautionPeaceful · 15 cm · Easy care · 25–30 °C (77–86 °F)
- Your 75 L tank is below the ~115 L this pairing really wants — crowding raises aggression.
- Rainbow Cichlid⚠️ With cautionSemi-aggressive · 14 cm · Easy care · 22–28 °C (72–82 °F)
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 75 L tank is below the ~130 L this pairing really wants — crowding raises aggression.
- Spotted Talking Catfish⚠️ With cautionPeaceful · 15 cm · Easy care · 22–26 °C (72–79 °F)
- Your 75 L tank is below the ~110 L this pairing really wants — crowding raises aggression.
- Yoyo Loach⚠️ With cautionSemi-aggressive · 15 cm · Medium care · 24–30 °C (75–86 °F)
- Swordtail and Yoyo Loach can both be territorial; doable with space and dense planting, but watch for chasing.
- Your 75 L tank is below the ~115 L this pairing really wants — crowding raises aggression.
- Alligator Gar⛔ Not recommendedAggressive · 250 cm · Hard care · 24–28 °C (75–82 °F)
- Two assertive fish, one genuinely aggressive: Swordtail and Alligator Gar will hold territory and clash.
- Alligator Gar (250 cm) is big enough to swallow the 14 cm Swordtail whole.
- Your 75 L tank is below the ~3785 L this pairing really wants — crowding raises aggression.
- Clown Knifefish⛔ Not recommendedAggressive · 90 cm · Hard care · 24–28 °C (75–82 °F)
- Swordtail and Clown Knifefish are both territorial and at least one is outright aggressive — expect serious fighting.
- Swordtail is bite-sized to a 90 cm predatory clown knifefish — it will be eaten.
- Your 75 L tank is below the ~750 L this pairing really wants — crowding raises aggression.
- Fire Eel⛔ Not recommendedSemi-aggressive · 100 cm · Medium care · 24–28 °C (75–82 °F)
- Fire Eel (100 cm) is big enough to swallow the 14 cm Swordtail whole.
- Both are a bit pushy (semi-aggressive + semi-aggressive) — workable only in a larger tank with cover and broken sight lines.
- Your 75 L tank is below the ~380 L this pairing really wants — crowding raises aggression.
- Koi⛔ Not recommendedPeaceful · 90 cm · Medium care · 4–28 °C (39–82 °F)
- Swordtail is bite-sized to a 90 cm koi — it will be eaten.
- Your 75 L tank is below the ~3800 L this pairing really wants — crowding raises aggression.
- Redtail Catfish⛔ Not recommendedAggressive · 120 cm · Hard care · 24–27 °C (75–81 °F)
- Two assertive fish, one genuinely aggressive: Swordtail and Redtail Catfish will hold territory and clash.
- Swordtail is bite-sized to a 120 cm predatory redtail catfish — it will be eaten.
- One likes softer water and the other harder (12–25 vs 3–10 dGH) — a compromise, not a perfect match.
- Your 75 L tank is below the ~5700 L this pairing really wants — crowding raises aggression.
- Spotted Gar⛔ Not recommendedAggressive · 90 cm · Hard care · 18–26 °C (64–79 °F)
- Two assertive fish, one genuinely aggressive: Swordtail and Spotted Gar will hold territory and clash.
- Size gap is too large (90 vs 14 cm): Spotted Gar will treat Swordtail as food.
- Your 75 L tank is below the ~600 L this pairing really wants — crowding raises aggression.
- Wels Catfish⛔ Not recommendedAggressive · 300 cm · Hard care · 15–25 °C (59–77 °F)
- Two assertive fish, one genuinely aggressive: Swordtail and Wels Catfish will hold territory and clash.
- Swordtail is bite-sized to a 300 cm predatory wels catfish — it will be eaten.
- Your 75 L tank is below the ~20000 L this pairing really wants — crowding raises aggression.
- Wolf Cichlid⛔ Not recommendedAggressive · 72 cm · Hard care · 24–30 °C (75–86 °F)
- Swordtail and Wolf Cichlid are both territorial and at least one is outright aggressive — expect serious fighting.
- Size gap is too large (72 vs 14 cm): Wolf Cichlid will treat Swordtail as food.
- Your 75 L tank is below the ~760 L this pairing really wants — crowding raises aggression.
Compatibility is computed from each species' care data — a strong starting point, not a guarantee. Individual temperament varies, so always introduce new fish slowly and watch them.
Swordtail care specs
- Care level
- Easy
- Breeding
- Easy
- Max size
- 14 cm (5.5 in)
- Min tank size
- 75 L (19.8 gal)
- Temperature
- 22–28 °C (72–82 °F)
- pH
- 7–8.3
- Hardness
- 12–25 dGH
- Lifespan
- 3–5 years
- Diet
- Omnivore
- Swim level
- Middle
- Group size
- 3+ (shoaling)
- Family
- Poeciliidae
- Origin
- Central America — Mexico, Guatemala, Honduras and Belize (rivers and streams)
What is a swordtail?
The swordtail (Xiphophorus hellerii) is a hardy, mid-sized livebearer from Central America and one of the oldest fixtures in the freshwater hobby. Males are immediately recognisable by the elongated lower lobe of the tail fin — the “sword” — that can rival or exceed the body length itself, giving an overall size of up to 14 cm (5.5 in). Females grow stockier and rounder but lack the sword entirely.
Decades of selective breeding have pushed the colour palette well beyond the wild olive-green: red velvet, pineapple, koi, wagtail and black-bar forms are all common in shops. The swordtail is a close relative of the platy (X. maculatus) and the two species will hybridise readily, so keep them apart if you want to maintain true strains.
Its combination of striking looks, straightforward care requirements and lively personality has kept the swordtail near the top of beginner fish lists for generations — though “easy” does not mean effortless, and a few key decisions (tank size, stocking ratio, lid) determine whether keeping them is a pleasure or a headache.
Where do swordtails come from?
Wild swordtails are native to Central America — principally Mexico, Guatemala, Honduras and Belize — where they inhabit fast-flowing rivers, streams and springs. The water in these habitats tends to be clear, hard and alkaline, with good flow and a mix of rocky substrate and aquatic vegetation.
That origin has direct consequences for aquarium care: swordtails are not a soft-water fish. They evolved in mineral-rich environments and do best in conditions that would suit a molly or platy. Warm, neutral-to-alkaline, moderately hard water replicates their home well. Soft, acidic conditions common in blackwater setups are unsuitable.
What size tank does a swordtail need?
The minimum is 75 litres (20 gallons) for a small group, and the shape matters as much as the volume. Swordtails are active, open-water swimmers that need horizontal run — choose a tank that is longer than it is tall rather than a tall show tank. A standard 90 cm (36 in) aquarium is a practical starting point.
Because males can be pushy with each other and with females, more space and more visual breaks (plants, rocks, decor) directly reduce conflict. If you want to keep more than one male, a 150 L (40 gal) or larger tank with dense planting gives everyone enough territory to avoid constant sparring. Swordtails appreciate a gentle-to-moderate current, consistent with their river origins, but still need enough open swimming room.
What water parameters do swordtails need?
- Temperature: 22–28 °C (72–82 °F). They tolerate the lower end better than most tropical fish but thrive in the mid-range.
- pH: 7.0–8.3. Neutral to moderately alkaline — this is important. Do not keep swordtails in acidic conditions.
- Hardness: 12–25 dGH. Moderately hard to hard water is ideal. Soft-water tanks benefit from the addition of crushed coral or limestone in the filter to buffer pH upward.
As with all fish, stability beats perfection. Weekly water changes of 25–30% and a fully cycled tank are the most important factors. Swordtails are relatively tolerant of fluctuation compared to delicate species, but chronically poor water still shortens lives and suppresses colour.
What do swordtails eat?
Swordtails are omnivores and unfussy feeders, which is part of what makes them beginner-friendly. A quality flake or small pellet as the daily staple covers their nutritional needs adequately. Supplement two or three times a week with frozen or live daphnia, brine shrimp, bloodworm or mosquito larvae — this brings out better colour and keeps the fish engaged.
They will also graze on soft algae and accept blanched vegetables such as spinach or zucchini. Feed small amounts once or twice a day, enough to be consumed in two to three minutes. Swordtails are enthusiastic eaters and can appear permanently hungry; resist the temptation to overfeed, as excess waste degrades water quality quickly in a livebearer tank.
Are swordtails aggressive — and what fish can live with them?
Swordtails are classed as semi-aggressive, and the aggression is almost entirely male-on-male and male-on-female harassment. A dominant male will chase rivals relentlessly and can stress females into hiding or early death if the tank is too small or overstocked with females.
The golden rule: one male per tank in any aquarium under 150 L (40 gal), paired with at least two females per male to spread the male’s attention. In a larger, heavily planted tank, two males can sometimes coexist if they can establish separate territories, but this is not guaranteed and requires close observation.
Towards other species, swordtails are generally peaceful. They work well with platies, mollies, corydoras, tetras that prefer hard water (such as black skirt or emperor tetras), gouramis and similarly sized peaceful mid-water fish. Avoid very small, slow or long-finned fish that could be nipped or outcompeted at feeding time. For a full breakdown of compatible and incompatible species, see Swordtail tank mates.
Keep a group of at least 3 (ideally one male and two or more females) so social behaviour remains natural.
How do you tell male and female swordtails apart?
Sexing adult swordtails is among the easiest tasks in the hobby. Males carry the defining elongated lower tail lobe — the sword — which may be yellow-edged in some colour forms, and their anal fin is modified into a narrow, rod-like gonopodium used for internal fertilisation. Males are also slimmer and generally smaller in body (despite the added tail length).
Females are noticeably larger and rounder in the body, with a conventional, unmodified tail and fan-shaped anal fin. A gravid (pregnant) female develops a dark gravid spot near the anal vent as a brood of fry develops internally.
One unusual note: swordtails occasionally undergo sex reversal — older females, particularly those that have already bred, can develop male colouration and a gonopodium. This is a genuine biological phenomenon, not a misidentification, and the fish typically become reproductively functional males.
How do swordtails breed?
Swordtails are livebearers, meaning the fry are born free-swimming rather than hatching from eggs. Breeding is virtually inevitable in a mixed-sex tank — no special setup, conditioning or triggering is required. A female stores sperm after a single mating and can produce successive broods of 20–80 fry every four to six weeks without needing to mate again.
Fry are large enough at birth to accept crushed flake or baby brine shrimp immediately. The main challenge is not getting them to breed but managing the population: adult swordtails and tank-mates will eat fry readily, which provides natural population control in a community tank. If you want to raise fry, move heavily pregnant females to a well-planted or net breeder, or add dense floating plants (hornwort, water lettuce) to give fry hiding cover in the main tank.
We rate breeding difficulty as easy — the fish do the work; your role is managing the results.
What are common swordtail diseases?
Swordtails share the disease profile typical of livebearers kept in suboptimal conditions:
- Ich (white spot): Fine white spots across the body and fins. Usually triggered by temperature drops or stress from transport. Prevention: stable temperature, quarantine new arrivals.
- Fin rot: Ragged, browning fin edges, almost always a water-quality problem. Prevention: consistent water changes and avoiding overcrowding.
- Velvet: A fine golden or rust-coloured dust on the skin. More common in weakened fish. Prevention: good nutrition and stable water.
- Wasting / internal parasites: Thin fish that eat well but lose condition, sometimes with a pinecone-like raised scale appearance. Prevention: buy from reputable sources and quarantine new stock.
- Swim-bladder issues: Difficulty maintaining position, often from overfeeding or constipation. Prevention: varied diet with occasional fasting days.
The most reliable disease prevention for swordtails is the same as for any livebearer: hard, alkaline, well-maintained water; no overcrowding; and a 2–4 week quarantine for every new addition before it enters the main tank.
Health note: disease identification and medication choices are beyond the scope of a care profile. Confirm your diagnosis against a reputable veterinary or fish-health source before treating, and address water quality first — most livebearer ailments are secondary to environmental stress.
How long do swordtails live?
A well-kept swordtail lives 3–5 years. Males that are spared constant fighting and females that are not over-bred tend to reach the upper end of that range. Because livebearers reproduce so readily, shop-bought swordtails are sometimes older than they look — buying from a reputable breeder who can give an approximate age helps.
Consistent water quality, a varied diet and a low-stress social environment (appropriate stocking ratios, enough space, a secure lid to prevent jumping) are the factors that most reliably push swordtails toward the five-year mark.
Frequently asked questions
Will swordtail males fight each other?
Yes — keep only one male per tank unless the aquarium is large (150 L+) with plenty of visual breaks. Multiple males will spar constantly. A ratio of two or more females per male keeps aggression manageable and spares the females from non-stop harassment.
Do swordtails need a lid on the tank?
Absolutely. Swordtails are strong, enthusiastic jumpers, especially when startled or chasing each other. A well-fitted lid or cover is essential — gaps around filters and heaters are enough for them to squeeze through and jump out.
What you need to keep a swordtail
The baseline is a heated, filtered 75 L+ tank: a reliable heater to hold 22–28 °C (72–82 °F), a gentle filter that won't batter a swordtail in the current, and a tight-fitting lid. Cycle the tank fully before adding any fish.
As an Amazon Associate we earn from qualifying purchases — buying through these links costs you nothing extra.
