Swordtail

Xiphophorus hellerii

The swordtail (Xiphophorus hellerii), often called the green swordtail in its wild form, is a livebearing freshwater fish native to Atlantic-slope streams and rivers from eastern Mexico into Central America. Males are easy to recognize by the elongated lower edge of the tail fin, the sword, along with a gonopodium used in mating; females are usually larger and lack the tail extension. Wild fish are greenish with a lateral stripe, but aquarium lines include red, tuxedo, wagtail, lyretail, and many other color forms, some shaped by long-standing hybridization with platies.

Aquarists keep swordtails in roomy, covered tanks because they are active swimmers and capable jumpers. They do best in clean, moderately warm, mineral-rich water with plants or hardscape that let females and young fish avoid persistent males. A mixed omnivore diet of quality prepared foods, algae or vegetable matter, and small invertebrate foods supports good condition. Breeding is easy: females store sperm and give birth to live fry, so population control and fry protection become practical concerns. Unwanted swordtails should never be released outdoors, where livebearers can establish feral populations and affect native waterways.