Home / Fishes / Killifish and livebearers / Green swordtail
No federal permit to keepGreen swordtail
Xiphophorus hellerii
Fishes › Killifish and livebearers (Cyprinodontiformes) › Poeciliidae (Livebearers)
The green swordtail (Xiphophorus hellerii) is a species of freshwater/brackish fish in family Poeciliidae of order Cyprinodontiformes.
Care at a glance
Species-specific aquarium care
- Tank: At least 24 in long and 12 in front to back for one adult (adults commonly reach about 1.1 in / 2.75 cm; the largest recorded was 5.5 in).
- Water: Freshwater (tolerates brackish).
- Temperature: 72–82°F (range recorded for this species).
- pH: 7–8.
- Hardness: 9–19 dGH.
- Layout: Uses both the bottom and open water: give open swimming space plus cover near the substrate.
- Diet: Eats a varied diet: mix quality prepared foods with frozen and live foods. FishBase classes it as a carnivore.
Calculated from this species' own FishBase record: tank size from its typical adult length and swimming zone, water values from its recorded ranges. The group guide below fills in general care.
Care guide
Species care notes
- Tank: a base of at least 47 × 12 in (roughly 29 US gallons); space needed is rated “large tank”.
- Water: a fairly wide range, from slightly acidic to slightly alkaline, 61–82 °F, pH 7–8, 10–25 dGH.
- Behaviour: a shoaling fish best kept in a group of six or more; suited to a community tank.
- Difficulty: Moderate (Seriously Fish rating).
Short excerpts from the species profile:
- Setup: “Choice of décor is not especially critical though it tends to look best in a heavily-planted set-up with a dark substrate.”
- Diet: “Stomach analyses of wild specimens have shown it to be a generalised omnivore, feeding on a range of aquatic and terrestrial invertebrates, organic detritus, algae, and other plant material.”
- Tankmates: “In confined spaces groups of males tend to form dominance hierarchies and may invest a significant proportion of time maintaining their respective positions.”
- Breeding: “Like other members of the viviparous family Poeciliidae, male Xiphophorus have a gonopodium, essentially a modified anal-fin, which is used for internal fertilisation of females.”
From the Seriously Fish profile for this species, which has the full habitat, maintenance, diet, behaviour and breeding write-up 167
Livebearers (guppies, mollies, platies and swordtails)
Applies to most species in this group. Habitat: Warm streams, ponds and brackish waters. Individual species can differ, so compare with the species numbers above and the linked sources.
Housing & setup
- Planted tanks with gentle flow; mollies appreciate harder, slightly brackish water.
Diet
- Flake foods with plant matter, plus live or frozen foods.
Social life
- Peaceful community fish; keep more females than males.
Health watch
- They breed constantly; plan for fry or keep single-sex groups.
Understanding the animal
About this animal
About this animal
A live-bearer, it is closely related to the southern platyfish or 'platy' (X. maculatus) and can crossbreed with it. It is native to an area of North and Central America stretching from Veracruz, Mexico, to northwestern Honduras.
Quoted from the Wikipedia article “Green swordtail” (CC BY-SA 4.0) 174
In the wild
In the wild
From this species’ own FishBase record (habitat, bottom type, water and breeding data), not its family. Good care copies these conditions.1
| Where it lives | Lives in freshwater and brackish water. Uses both the bottom and open water. Adults are found mainly in rapidly flowing streams and rivers, preferring heavily vegetated habitats. |
| Water it lives in | Freshwater / brackish water, 72–82 °F (22–28 °C), pH 7–8, hardness 9–19 dH. |
| Climate | Tropical climate. |
| Behavior to plan for | Breeding: internal live bearers. |
What this means for care
- Keep water within its wild range, 72–82 °F.
- It tolerates or needs brackish water; check salinity needs before setup.
Native climate (measured)
Native climate (measured)
| Warm-season highs | about 90°F (up to 96°F in the hottest sampled areas) |
| Cool-season lows | about 60°F (down to 39°F in the coldest sampled areas) |
| Average temperature | 61–79°F across sampled records |
| Relative humidity | 65–78% on average (driest month about 68%) |
| Rainfall | about 1497 mm a year |
Measured at 279 wild occurrence records sampled against WorldClim 2.1 climate data (1970–2000 averages). Air conditions in the range are ecological context, not enclosure settings: microhabitats such as burrows, leaf litter or basking rocks can be cooler, warmer or more humid.
From the sources
From the sources
Quoted from the matching sections of reputable sources for this exact species. Specialist databases are used first; Wikipedia (community-edited, CC BY-SA 4.0) only fills gaps. Other sources are short credited quotes.
| Overview | The green swordtail (Xiphophorus hellerii) is a species of freshwater/brackish fish in family Poeciliidae of order Cyprinodontiformes. A live-bearer, it is closely related to the southern platyfish or 'platy' (X. maculatus) and can crossbreed with it. It is native to an area of North and Central America stretching from Veracruz, Mexico, to northwestern Honduras. — Wikipedia (community-edited) |
| Where it lives | Home ranges Population dynamics Growth parameters Max. ages / sizes Length-weight rel. Length-frequencies Mass conversion Recruitment Abundance Life cycle Reproduction Maturity Maturity/Gills rel. — FishBase |
| Reproduction | Female produces 20 to 200 young after a gestation period of 24 to 30 days. Attains sexual maturity after eight to twelve months. This species has a tendency to undergo sex reversal (from female to male) under certain environmental conditions. — FishBase |
| Appearance and size | The male green swordtail grows to a maximum overall length of 14 cm and the female to 16 cm. The name 'swordtail' is derived from the elongated lower lobe of the male's caudal fin (tailfin). Sexual dimorphism is moderate, with the female being larger than the male, but lacking the 'sword'. — Wikipedia (community-edited) |
| Biology | Adults are found mainly in rapidly flowing streams and rivers, preferring heavily vegetated habitats. They occur in warm springs and their effluents, weedy canals and ponds. They feed on worms, crustaceans, insects and plant matter. — FishBase |
| History and naming | The binomial of the green swordtail is made up of its generic name, Xiphophorus which means sword bearer in Greek, a reference to the extended lower part of the caudal fin which is referred to as the "sword". The specific name honours the collector of the type, the Austrian botanist Karl Bartholomaeus Heller (1824–1880), who discovered this fish while exploring México in 1845–1848. — Wikipedia (community-edited) |
Data and studies
The numbers
The numbers
Each bar is what one source reports. Where several sources weigh in, the dashed gold band marks their average.
Maximum recorded lifespan
Longest recorded lifespan reported by each database; typical lifespans are usually shorter. The AnAge record comes from an animal in human care.
Adult length
Common length to maximum recorded length. Measured as total length. Fish in home aquariums often stay smaller than wild records.
Water temperature
Range the species tolerates in nature; aim for the middle.
Female maturity
Minimum tank footprint
Seriously Fish recommends a tank base of at least 47 × 12 in (about 29 US gallons).
Veterinary & husbandry research
Veterinary & husbandry research
- Morphological and molecular description of eight new species of Gyrodactylus von Nordmann, 1832 (Platyhelminthes: Monogenea) from poeciliid fishes, collected in their natural distribution range in the Gulf of Mexico slope, Mexico García-Vásquez A et al., Parasitology research 2015
- Comparison of Morphological Characteristics, Histological Tissue Structures, and Intestinal Function Among Eight Ornamental Fish Species Under Identical Aquaculture Conditions Xie M et al., Biology 2026
- Record of Urocleidoides vaginoclaustrum Jogunoori, Kritsky and Venkatanarasaiah, 2004 (Monogenea: Dactylogyridae) from a freshwater fish in Mexico Mendoza-Palmero CA et al., Parasitology research 2008
Peer-reviewed papers that mention this species alongside captivity, zoos, veterinary care or aquaculture. Some cover several species or mention it only in passing, so check the abstract. 170
Sources for this sheet
- AnAge: The Animal Ageing and Longevity Database (Human Ageing Genomic Resources) Peer-reviewed researchCurated, referenced longevity and life-history records for thousands of species; maximum lifespans are often from zoo animals.
- FishBase (Froese & Pauly, eds.), version 24.07 Peer-reviewed researchThe global scientific database on fishes, maintained by a consortium of research institutions; every value is referenced.
- Seriously Fish species profiles Experienced keeper or breederLong-running aquarium reference written and peer-checked by experienced fishkeepers and ichthyologists; each profile covers habitat, tank size, water, diet, behaviour and breeding.
- Merck Veterinary Manual: Management of aquarium fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Merck Veterinary Manual: Types and features of aquatic systems Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Merck Veterinary Manual: Nutritional diseases of fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
- Wikipedia (species article) Community referenceFree encyclopedia; useful overviews with their own citations. Intro text is quoted under CC BY-SA 4.0.
- PubMed (U.S. National Library of Medicine) Peer-reviewed researchIndex of peer-reviewed veterinary, zoo and husbandry research.
- iNaturalist (captive observations) Community referenceCommunity observation platform run by the California Academy of Sciences and National Geographic; observations marked captive show animals living in homes, zoos and aquariums.
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