Green swordtail

Xiphophorus hellerii

FAMILY

Poeciliidae

TAXONOMY

Xiphophorus hellerii Heckel, 1848, Orizaba, Mexico.

OTHER COMMON NAMES

English: Swordtail; Spanish: Cola de espada.

PHYSICAL CHARACTERISTICS

Males grow to 5.5 in (14 cm) in total length, with a sword length of 1.6–3 in (4–8 cm). Females grow to 6.3 in (16 cm). Sexually dimorphic. Males and females have basically the same grayish green background color. Males have a gonopodium, a slender body, a long extension on the bottom of the caudal fin forming a "sword," two lines of reddish dots on a squared-off dorsal fin, and a pronounced line of color that is bright to dark red to almost brown running longitudinally along the body from the snout through the eye to the base of the caudal fin. Sometimes paralleled on the flanks by one or two fainter reddish lines above and below. The sword is an iridescent yellowish green bordered in black. Females are robust and rounded, with squared-off anal and dorsal fins. Caudal fin is asymmetrically rounded, with a hint of a protrusion from the lower part of the fin. There is a shadow on the area over the vent (gravid spot).

DISTRIBUTION

Native distribution in Rio Nantla, Veracruz, Mexico, to northwestern Honduras. Naturalized in the continental United States (ten states) and Hawaii; Michoacan, Morelos, Nuevo Leon, and Coahuila, Mexico; Transvaal, South Africa; Sri Lanka; New Caledonia, Australia; Fiji; Guam; Réunion; and Madagascar.

HABITAT

Inhabit rivers, streams, warm springs and their runoffs, canals, and ponds with heavy vegetation.

BEHAVIOR

While they are not territorial, male swordtails form hierarchical groups. A dominant male drives off rivals within a feeding domain or an area where females have congregated. The mating success rate of a dominant male is about 80% within his area of activity. Females form hierarchical groups of several individuals that stay in close proximity to a dominant male.

FEEDING ECOLOGY AND DIET

Plant material and insects form the greatest part of the diet. In aquaria they are voracious, consuming a wide variety of foods, such as fruit flies, frozen or live brine shrimp and chironomid larvae, flake foods, high-protein paste foods, small fish, and algae.

REPRODUCTIVE BIOLOGY

Green swordtails are live-bearers. Males impregnate females by means of a gonopodium. Females can store sperm and may produce, from a single mating, several broods over an eight-month period. Swordtails undergo lecithotrophic (type 1) gestation and development, with fry being produced approximately every 30 days. Brood sizes are fairly large; 100 or more fry may be produced by a large female.

CONSERVATION STATUS

Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

The green swordtail has considerable economic importance in the aquarium trade and frequently is used in genetic and behavioral research.

Green Swordtail
Conservation status
Secure
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cyprinodontiformes
Family:	Poeciliidae
Genus:	Xiphophorus
Species:	X. hellerii
Binomial name
Xiphophorus hellerii Heckel, 1848

For the genus of butterflies commonly known as swordtails, see Graphium.

The Green swordtail (Xiphophorus hellerii) is a species of freshwater fish in family Poeciliidae of order Cyprinodontiformes. A live-bearer, it is closely related to the southern platyfish or "platy" (X. maculatus) and can interbreed with it. It is native to an area of North and Central America stretching from Veracruz, Mexico, to northwestern Honduras.

The male green swordtail grows to a maximum overall length of 14cm (5.5in) and the female to 16 cm (6.3 in). 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 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.

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.

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 Natal, Madagascar and eastern Transvaal in South Africa and Otjikoto Lake in Namibia. Significant populations have also established themselves along the east coast of Australia.

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.

The green swordtail, as the most common of the swordtail species (and in recognition of the fact that many captive-bred color varieties are not green), is typically known simply as the swordtail in the aquarium hobby. It is often designated X. helleri (with one i), but authorities consider this an orthographic error and the spelling with two is is the valid specific epithet. Due to interbreeding with the southern platyfish or "platy" most "swordtail" in the aquarium 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.^[1][2][3]

Cultivated form of X. hellerii.

References

1. ^ "In the science of sexual attraction, size matters" (in english). Yahoo! Science News (Yahoo! Inc). 2007-02-13. http://news.yahoo.com/s/nm/20070214/sc_nm/science_size_dc_1. Retrieved 2007-02-14. 
2. ^ Choi, Charles Q. (2007-02-13). "Male Bling Makes Female Fish Mature Faster". LiveScience Animaldomain (Imaginova Corp.). http://www.livescience.com/animalworld/070213_sight_sex.html. Retrieved 2007-02-14. 
3. ^ Choi, Charles Q. (2007-02-13). "Male Bling Makes Female Fish Mature Faster". Yahoo! Science News (Yahoo!, Inc.). http://news.yahoo.com/s/livescience/20070214/sc_livescience/maleblingmakesfemalefishmaturefaster. 

External links

Wikimedia Commons has media related to: Xiphophorus helleri

• "Xiphophorus hellerii". FishBase. Ed. Ranier Froese and Daniel Pauly. October 2004 version. N.p.: FishBase, 2004.
• Xiphophorus hellerii (TSN 647013). Integrated Taxonomic Information System. Retrieved on 9 December 2004.
• Xiphophorus maculatus (Spanish)

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