Green Swordtail

Looks how to spot one

Scaled livebearer (family Poeciliidae) with a sword-shaped tail extension in males

A sleek, torpedo-shaped fish. Wild-type fish are olive green with a red to brown stripe along the flank and small speckles on the dorsal fin. Mature males grow a long, narrow extension from the bottom edge of the tail fin, usually yellow with a black lower border, and carry a gonopodium (a modified anal fin). Females are the larger sex, reaching up to about 16 cm, and have a plain fan-shaped tail.231

Personality what they are like

Generally a calm, sociable community fish that gets along with other peaceful species of similar size. Males sort themselves into a pecking order and spend a lot of energy displaying to one another, so a single male or one male with three or four females keeps things relaxed. Active swimmers that like to explore the whole tank.3241

Daily activity how busy a day looks

Lively, fast swimmers that use the full length of the tank and come from flowing streams, so they enjoy open swimming space and some water movement. They are capable jumpers, so a tight-fitting lid is a good idea.351

Grooming and care the hands-on bits

Keep the water warm, clean and on the hard, alkaline side with regular partial water changes. Suggested ranges: about 22-28 C (tolerates down to around 16 C), pH 7.0-8.0 (some sources up to 8.4), hardness roughly 9-25 dGH. Cover the tank because swordtails can leap out.1345

Home where they are happiest

A long tank suits them best. FishBase gives an 80 cm minimum length, while Seriously Fish recommends a footprint of about 120 x 30 cm (roughly 108 litres) for a group. Include dense planting around the sides and back with open water in the middle; a darker substrate shows off wild-type colours.13

Food basics what goes in the bowl

An omnivore that eats small invertebrates, algae and plant matter in the wild. In the aquarium it takes good-quality flakes and small pellets, plus vegetable matter and treats such as daphnia, brine shrimp or frozen bloodworm.1324

Company who they like around

Best kept in a group with more females than males, commonly one male to three or four females, which spreads out male attention and limits squabbles between males. Mixes well with other peaceful community fish such as platies, mollies, corydoras and gouramis.243

The story where it all began

The species takes its name from the Austrian botanist Karl Bartholomaeus Heller, who collected fish while exploring Mexico between 1845 and 1848. Johann Jakob Heckel formally described it in 1848, using fish from Orizaba in Mexico, and it became the type species of the genus Xiphophorus, whose name means 'sword bearer' in Greek. Several later names, such as X. guntheri and X. jalapae, have since been folded into this species. Thanks to its hardiness and how easily it breeds, the swordtail became one of the most familiar tropical aquarium fishes worldwide. Breeders crossed it with the southern platy and the variable platy, and most swordtails sold today carry some platy ancestry, which is where many of the red, black, tuxedo and wagtail forms come from. Swordtails and platies have also been important laboratory fish for genetics since the 1920s, and the Xiphophorus Genetic Stock Center, founded by Myron Gordon in 1939, keeps pedigreed lines for researchers. Nearly all fish in the hobby today are captive bred.235

Recognised by the official bits

IUCN Red List

Assessed as Least Concern (assessment dated 29 March 2018, published 2019)1

FishBase

Listed as highly commercial in the aquarium trade; red varieties singled out as especially popular1