The Green Swordtail (Xiphophorus hellerii) is a species of freshwater fish native to an area of North and Central America stretching from Veracruz, Mexico, to northwestern Honduras. It has been introduced to a number of countries and has become a nuisance pest. 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 Lake Otjikoto in Namibia. Significant populations have also established themselves along the east coast of Australia. The swordtail prefers swift-flowing, heavily-vegetated rivers and streams, but is also found in warm springs and canals.
The male green swordtail grows to a maximum length of 5.5 inches. The female grows to about 6.3 inches. The name “swordtail” is often mistakenly thought to be derived from the elongated lower lobe of the male’s tailfin, but it is actually derived from the sword shaped anal fin of the male. Females lack the sword feature. In the wild, these fish are green in color, with a red or brownish lateral stripe and speckles on the dorsal and, often, tailfins. The male’s “sword” is yellow and edged in black below. Many color variations have been produced in captive breeding.
The green swordtail is an omnivore. Its diet consists of both plants and small crustaceans, insects, and annelid worms. 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 males’ elongated caudal fins have been found to significantly affect their chances at mating.