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Family: Poeciliidae, Subfamily Poeciliinae

Common Names: Swordtail

Origin and Habitat: North and Central America, from the Rio Nantla, Veracruz in Mexico to northwestern Honduras. Introduced to areas in Africa, and in several states in the USA. Occurs mainly in fast-flowing streams and rivers, preferring heavily vegetated areas; also in warm springs, weedy canals and ponds.
Compatibility/Temperament: Peaceful, though males can be aggressive especially as they mature. Should not be kept with small fish, nor larger aggressive species. Being active, it is not suited to tanks with slow sedate fish. Should not be kept with other livebearers, especially platy and guppy, as it will likely interbreed. Males may be housed without females; if females are included, there should be several females for each male to avoid stress from the attentions of males.

Swordtail Diet

Naturally feeds on insects, worms, crustaceans and plant matter including algae. In addition to good quality prepared foods, frozen (or live) bloodworms, brine shrimp, daphnia, wingless fruit flies, mosquito larvae. Blanched vegetables such as spinach, yam and zucchini.


As an adult Swordtails range from four to as large as six inches; in aquaria 4-5 inches is normal, with females slightly larger than males. You will commonly find them from two to three inches in pet shops. At that size they are generally six to nine months old.

Minimum Tank Suggestion

30 inches in length (20g long or a 29g) to provide swimming space.

Water parameters for Swordtail

Medium hard to hard (9-30 dGH), basic (pH 7 to 8), temperature 20-28C/68-82F. Better at temperatures in the lower part of the given range. This species like all livebearers will not last in soft, acidic water.


Swordtails have long been found in the aquarium trade and are by far one of the most popular poeciliids. The original wild fish is the common green form with minimal red markings. Due to cross-breeding with platy (which are in the same genus) from the species X. maculatus and X. variatus, swordtails are now available in a variety of colour forms and finnage including hifin, wagtail, lyretail and tuxedo, with fish that are completely red or mixed red and black in addition to the original green with red.

Males sport the "sword" which is an extension on the lower edge of the caudal fin; this is absent on females. In addition to the sword, the male's anal fin is modified into a gonopodium by which he transfers sperm into the female. This is the most reliable means of determining the sex of the fish; as mentioned under temperament, if both sexes are to be housed in the same aquarium, there should be more females than males to provide some rest for the females from the attention of the males. Maintaining males and females in the same tank will result in regular batches of fry approximately every 28 days, and once impregnated, a female can deliver several successive batches on her own [this is known as superfetation]. In fry, this impregnation can occur before the males attain their colouration, so fish must be separated out very early if the aquarist wishes to selectively breed them.

There are reports of swordtails changing their sex. In some cases this may simply be a slower development, but some adult females have been known to develop male characteristics that might be due to infertility.

No particular effort is needed in breeding them and eventually rearing the fry as the fry themselves are well developed enough to eat finely-ground prepared foods and brine shrimp nauplii. Fry require hiding places such as thick floating plant cover, or they will be readily eaten by the adults. All breeder traps are best avoided as they have the tendency to stress swordtails to death. Fry become sexually mature by 2-3 months depending on the conditions provided to them.

The aquarium should be well planted and have a moderate flow from the filter. Creating a stream habitat would be ideal; the substrate may be fine gravel, with river rock replicating boulders. This fish prefers to swim in the upper half of the aquarium. It has a life span of 3-4 years.

The species was described by J.J. Heckel in 1848 and is the type species for the genus Xiphophorus. The genus name is derived from the Greek xipho [=sword] and phorus [=bearer]. The species epithet honours an aquarist, C. Heller; the spelling with only one "i" is often encountered but is inaccurate. Five species described as X. brevis, X. guntheri, X. jalapae, X. rachovii and X. strigatus have subsequently been determined to be conspecifics [= the same species] and these names are now synonyms.

The subject species is the common swordtail seen regularly in the hobby. There are several other distinct species that are rarely available; Xiphophorus montezumae is probably the one that might be encountered over the remainder. Further information can be obtained from the American Livebearer Association.

Contributing Members

The following members have contributed to this profile: 1077, buckmanrules, Byron


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