Green Swordtail, Xiphophorus hellerii

Green Swordtail, Xiphophorus hellerii, Female. Caught from the Río Cuautla, Morelos, February 2017. Length: 5.6 cm (2.2 inches). Catch, photograph and identification courtesy of Ben Cantrell, San Diego, California.

Green Swordtail, Xiphophorus hellerii, Female. Fish caught from freshwater canal in the greater Miami, Florida area, February 2022. Length: 5.8 cm (2.3 inches). Catch, photograph and identification courtesy of James Lafontaine, Long Island, New York.

Green Swordtail, Xiphophorus hellerii, Female. Fish caught from a hotspring within Grand Teton National Park, Jackson Hole, Wyoming, June 2020. Length: 6.6 cm (2.6 inches). Catch, photographs and identifications courtesy of Luke Ovgard, Klamath Falls, Oregon.

Green Swordtail, Xiphophorus hellerii, Female. Fish caught from freshwater canal in the greater Orlando, Florida area, November 2020. Length: 6.6 cm (2.6 inches). Catch, photograph and identification courtesy of Ben Cantrell, San Diego, California.

Green Swordtail, Xiphophorus hellerii, Male. Caught from the Kelly Hot Springs, Grand Teton National Park, Wyoming, June 2020. Length: 7.7 cm (3.0 inches). Catch courtesy of Carson Moore, Peoria, Arizona. Photograph and identification courtesy of Chris Moore, Peoria, Arizona.

The Green Swordtail, Xiphophorus hellerii, is a member of the Livebearer or Poeciliidae Family, that is also known as the Red Swordtail and in Mexico as cola de espada. Globally, there are twenty-eight species in the genus Xiphophorus, the majority of which are found in Mexican waters, all within the freshwater drainage systems that drain into both the Atlantic and the Pacific Oceans. The Green Swordtail is closely related to the Southern Playtyfish, Xiphophorus maculatus. with which it will cross breed. They are named for the sword-like appearance of the male’s anal fin.

The Green Swordtail is moderate in size and is sturdy with an elongated body. They vary significantly in color with native fish being olive-green in color with a brown, red or yellow lateral stripe along the lateral line and speckles on the caudal and dorsal fins. The males sword is yellow with a black lower margin. Via breeding mutations occur so many fish will have many color variations including albino, black, green and red. They have a small terminal upturned mouth that is equipped with teeth on both the upper and lower jaws. Males are small and slimmer than females and have a “sword” on the lower lobe of the caudal fin that can be from one fourth to one third of the total length of the fish. Also, as the males mature, the middle rays of its anal fin modify into a narrow copulatory organ, the gonopodium. The female has a fan shaped anal fin, is rounder of body, and will have a spawning patch at breeding time.

The Green Swordtail is non-migratory and found in fast flowing heavily vegetated rivers and streams as-well-as canals and warm springs at depths up to 1.5 m (5 feet) at elevations up to 1,500 m (4,920 feet) in water temperatures between 18°C (65°F) and 28°C (82°F). Adults tend to congregate in areas with greater current, while juveniles and subadults display a preference for quiet marginal zones. They are sexually dimorphic with females have a maximum length of 16 cm (6.3 inches) and males 14 cm (5.5 inches); the females lack the sword found in the males. Their anal fin has 8 to 10 rays; their dorsal fin has 11 to 14 rays; their pectoral fins have 12 or 13 rays; and, their pelvic fins have 6 rays. They are omnivores that consume algae, annelid worms, small crustaceans, insects and plant materials. They have life spans of up to 5 years. They are preyed upon by various pelagic and surface predatory fish as well as numerous seabirds, including herons. Reproduction is ovoviviparous and has been studied extensively. Some can reach sexual maturity within 3 months of age. The males have a gonopodium, a modification of the anal fin, which is utilized for internal fertilization of the females. They generally form in groups of one male and several females for mating. The females are capable of storing viable male sperm for several months. Brood sizes are 20 to 40 individuals that are delivered by each female on a monthly basis.

The Green Swordtail is similar in appearance to the Guppy and the Platyfish with the females being difficult to separate visually. The males are easy to identify by the presence of the sword extending from the caudal fin.

The Green Swordtail is a resident of Mexico’s freshwater systems of the Atlantic Slope and found from Rio Nautla, Veracruz to Belize which includes the States of Campeche, Chiapas, Oaxaca, Quintana Roo, Tabasco and Veracruz. 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.

From a conservation perspective the Green Swordtail is currently considered to be of Least Concern with stable, widely distributed populations. They have been introduced in a wide number of countries and are now established on all continents except Antarctica. In some locations have become a nuisance pest causing ecological damage because of its ability to rapidly reproduce in high numbers. The Green Swordtail is one of the most popular tropical aquarium fish in the world due to beauty, striking male sword-like tail, hardiness, and peacefulness. They have the ability to be bred in captivity into various highly colored hybrid forms. They are very hardy and are suitable for community tanks. They have also been utilized as a laboratory animal in behavioral genetics and biomedical research.