The Swordtail or Xiphophorus helleri is a member of the family Poecilidae in the order Cyrinodontiformes.  The sword fish is endemic to both North and South America. Their natural habitat stretches from Vera Cruz, Mexico to Honduras.

The name swordtail is literal. These fish are named for the extended pointed region at the bottom of the caudal fin. This species is sexually dimorphic. The extended tail is found only among the males of the species. The different sexes do share the same color palette. The female is often slightly larger than the male.

Swordtails are related to another popular fish among freshwater aquarium owners, the plati commonly referred to as the southern platyfish. They are so closely related that they can crossbreed with one another and do so regularly in the wild.

Just like their cousin, the southern platyfish, the swordtail’s prolific breeding has wreaked havoc on previously uninhabited ecosystems. Feral populations can be found in both Africa and Australia.  This ecological nuisance has caused damage in both of  its new spawning grounds.

Like many of the fish you see in fish stores today, the swordtail has been selectively bred to increase its appeal for the aquarium owner. Swordtails come in an assortment of colors including orange, red, black, green, yellow and multi-colored varieties.

Swordtails have a good natured temperament. They are the perfect fit for community tanks. They prefer the swift moving water and heavy vegetation of tropical rivers and streams but can make themselves right at home in creeks and canals. Accordingly they can adapt to a multitude of aquarium conditions.

Swordtails thrive in slightly alkaline waters ranging from pH 7.0-7.3 with water temperatures between 72-79 °F. They can grow as long as 5 inches and have an average life expectancy of up to 5 years.

Swordtails are omnivorous. They are not picky eaters. They can subsist on a diet of nothing but tropical fish flakes but regular protein supplements will help maintain their virility and coloration.

The Swordtail is a live bearing fish. They share similar traits with other live bearers.  The males have a modified anal fin known as a gonopodium that is used to inseminate the female during spawning. They also have a tendency to harass the females of their species.  A mix of 2-3 females per male is recommended to curb incidences of domestic violence. Providing plants for the females to hide is also beneficial.

Swordtails commonly breed in community tanks. The urge to reproduce is so strong in this species that the females are hermaphroditic. In populations consisting entirely of females one will frequently transform into a male to insure the propagation of the species. The female will develop a dark gravid spot on her abdomen after she becomes pregnant. 

Fry have a four to six week gestation period. They will emerge from the female fully developed. Like most live bearing fish, adult swordtails will eat their fry. This can be easily avoided by the use of a breeding trap.
 
Fry can be fed newly hatched shrimp brine, powdered or liquid fry food formulated for live bearing fish. An economical and readily available substitute is powdered eggs.

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