The green swordtail (''Xiphophorus hellerii'') is a species of freshwater/brackish fish in family (biology), family Poeciliidae of order (biology), order Cyprinodontiformes. A live-bearing aquarium fish, 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 America, North and Central America stretching from Veracruz, Mexico, to northwestern Honduras.

Description

The male green swordtail grows to a maximum overall length of and the female to . 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'. The wild form is olive green in color, with a red or brown lateral stripe and speckles on the dorsal fin, dorsal and, sometimes, caudal fins. The male's 'sword' is yellow, edged in black below. Captive breeding has produced many color varieties, including black, red, and many patterns thereof, for the aquarium hobby. All varieties share the dark-red or brown central stripe. The green swordtail prefers swift-flowing, heavily vegetated rivers and streams, but is also found in warm springs and canals. Omnivorous, its diet includes both plants and small crustaceans, insects, and annelid worms.

Invasive species

''X. hellerii'' has become a nuisance pest as an introduced species in a number of countries. It has caused ecological damage because of its ability to rapidly reproduce in high numbers. Feral populations have established themselves in southern Africa, including KwaZulu-Natal Province, Natal, Hawaii, Madagascar and eastern Transvaal Province, Transvaal in South Africa and Otjikoto Lake in Namibia. Significant populations have also established themselves along the east coast of Australia.

Etymology and taxonomy

The binomial (biology), binomial of the green swordtail is made up of its Genus, generic name, ''Xiphophorus'' which means ''sword bearer'' in Greek language, Greek, a reference to the extended lower part of the caudal fin which is referred to as the "sword". The Specific name (zoology), specific name honours the collector of the Type (biology), type, the Austrian people, Austrian botanist Karl Bartholomaeus Heller (1824–1880), who discovered this fish while exploring México in 1845–1848. The green swordtail was Species description, described from Heller's type by Johann Jakob Heckel in 1848 with the Type locality (biology), type locality given as Orizaba, Mexico. It is the type species of the genus ''Xiphophorus''.

Aquarium fish

One of the most popular tropical aquarium fish, the green swordtail has been bred into various hybrid forms for the aquarium hobby due to its hardiness and suitability for community tanks. ''X. hellerii'' is a common laboratory animal and has been used as a model organism in studies involving female mate preference and male conflict. It is often designated ''X. helleri'' (with one 'i'), but authorities consider this an orthographic error and the spelling with two 'i's to be the valid specific epithet. It is named after Karl Bartholomaeus Heller, who collected the type specimen. Due to interbreeding with the southern platyfish or 'platy', most swordtails in aquariums are hybrids to some degree. The males' elongated caudal fins have been found to significantly affect their chances at mating. The presence of a well-endowed male spurs the maturity of females, while it inhibits the maturity of juvenile males in the vicinity of the well-endowed male.

Breeding

Swordtails are some of the easiest fish for amateur aquarist to breed, if the conditions of the tank are appropriate and it contains both males and females reproduction will occur without intervention. Often all female groups which have come from a mixed gender tank will be pregnant on arrival, creating a breeding population when the fry sexually mature at around three months of age. Later stages of pregnancy can be seen without much difficulty as a dark gravid spot will develop near the anal fin. Males can be distinguished from females by the presence of a Fish fin#Reproduction, Gonopodium, a modified anal fin used to impregnate the female during breeding. A ratio of one male to three or four females is recommended to ensure that individual females will not be overly harassed to breed. Plants and other structure in the aquarium will offer fry a place to hide after birth. This is important as newborn fry will be eaten by other aquarium inhabitants if they cannot find shelter.

Gallery

File:Swordtail cultivar.JPG, Cultivated form of ''X. hellerii'' File:Xiphophorus hellerii fry 01.jpg, Fry File:Xiphophorus hellerii red wagtail female 01.jpg File:Xiphophorus helleri Annanasschwerttaeger Maennchen.JPG

References

External links

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Xiphophorus maculatus (Spanish)Xiphophorus hellerii profile with photographs of various strains on Fishes N Inverts

Xiphophorus hellerii gallery with photographs of various strains on Fishes N Inverts
{{Taxonbar, from=Q272188 Xiphophorus Live-bearing fish Ovoviviparous fish Fish described in 1848 Fish of Mexico Taxa named by Johann Jakob Heckel