Xiphophorus hellerii

Xiphophorus: from the Ancient Greek ξίφος (ksíphos), meaning 'a kind of double-edged sword', and -φóρος (-phóros), meaning 'bearing', in allusion to the presence of a gonopodium in males of this genus.

hellerii: named in honour of Austrian botanist and naturalist Karl Bartholomaeus Heller (1824-1880), who explored Mexico between 1845-1848 and brought the type series of X. hellerii to Vienna.

Native to southeastern Mexico, central Guatemala, southern Belize, and northwestern Honduras. Its known range extends south from the Río Nautla (alternatively referred to as the Río Filobobos) in central Veracruz state, Mexico, to the Rio Usumacinta drainage in Guatemala, the Río Sarstún (aka Sarstoon) at the border between Guatemala and Belize, and the ríos Copán and Chamelecón in Honduras.

Within these boundaries it also occurs in various river systems in the Mexican states of Campeche, Chiapas, Oaxaca, Quintana Roo, and Tabasco.

Type locality is 'Orizaba, Mexico', which corresponds to the city of that name in Veracruz state.

It has been widely introduced to other river basins in Mexico and throughout the world, and is now present on all major continents except Antarctica. Countries or territories in which feral populations exist include Panama, Colombia, Brazil, Peru, Jamaica, Puerto Rico, Martinique, Bahamas, United States, Hawaii, Austria, Czech Republic, Hungary, Israel, Iran, Democratic Republic of the Congo, Namibia, South Africa, Zimbabwe, Zambia, Madagascar, Réunion, India, Sri Lanka, Singapore, China, Hong Kong, Taiwan, Japan, Indonesia, Guam, Papua New Guinea, Australia, New Caledonia, and Fiji.

Natural populations are found in various types of habitat from sea level to around 1500 m altitude, including fast-flowing, rocky streams, to springs, ditches, ponds, and rivers containing clear to turbid water. In most cases the water is less than 1.5 m deep and there is no aquatic vegetation.

In flowing water adults tend to congregate in areas with greater current, while juveniles and subadults display a preference for quiet marginal zones.

Introduced populations may occur in springs, streams, rivers, canals, ditches, pools, artificial reservoirs and other environments, and the species exhibits a degree of tolerance to polluted conditions. Where X. hellerii occurs in large numbers outside its natural range it is thought to exert a number of negative impacts on native species and ecosystems.

An aquarium with surface dimensions of 120 ∗ 30 cm48 ∗ 12 in or equivalent should be the smallest considered.

Choice of décor is not especially critical though it tends to look best in a heavily-planted set-up with a dark substrate. Wild forms should also suit an aquarium arranged to resemble a flowing stream with water-worn rocks and small boulders.

The addition of some floating plants and driftwood roots or branches to diffuse the light entering the tank also seems to be appreciated and adds a more natural feel.

Filtration does not need to be particularly strong though it does seem to appreciate a degree of water movement.

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.

In the aquarium it is unfussy and will accept just about anything offered. Offer a balanced diet comprising good quality dried products along with small live and frozen foods such as Daphnia, Artemia and chironomid larvae (bloodworm).

In confined spaces groups of males tend to form dominance hierarchies and may invest a significant proportion of time maintaining their respective positions.

Adult males tend to be smaller than females and possess a prominent gonopodium, plus the characteristic extension of the lower caudal-fin lobe. In some ornamental strains the upper caudal-fin lobe or other fins may also be extended, however, including in females.

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.

The reproductive behaviour of Xiphophorus is well-studied, and females are known to exhibit preferences for numerous physical and behavioural traits such as sword length (long, short, or without), colour pattern, body size, vertical barring on the body, chemical cues and specific nuptial behaviours. In some cases females show preferences for male traits of other species. Male behaviour is designed to both attract mates and drive away rivals, while some individuals, known as 'sneakers',

Females are also capable of storing viable male sperm for months,

This species is among the world's most recognisable aquarium fishes and ubiquitous in the ornamental trade, although its name is often misspelled X. helleri (with only a single i, vs. correct spelling X. hellerii) in both scientific and hobbyist literature.

Selective breeding has led to the development of a bewildering array of ornamental forms which tend to display colours, and often fin morphology, that are not present in wild fish. Some of these forms are also the result of artificial hybridisation with other members of the genus, particularly X. maculatus and X. variatus. See the images attached to this profile for some (by no means exhaustive) examples.

Xiphophorus species are naturally distributed throughout the Atlantic slope of Mexico and adjacent portions of Central America, although a number of members have been introduced to and become established in other countries and territories. In English they are commonly referred to as 'platyfishes' and 'swordtails', and are considered important in several fields of scientific research, including behavioural, genetic, and biomedical (including the cause and genetics of cancers) studies.

The genus is split into three main phylogeographic clades: the platies, or platyfishes, which occur throughout eastern Mexico and Central America; the northern swordtails, endemic to the Río Pánuco and Río Tuxpan watersheds in the Sierra Madre Oriental mountains of northeastern Mexico, and the southern swordtails of southern Mexico and northern Central America.

The relationships within these groups have also been studied in depth. X. hellerii is a member of the southern swordtail clade,