There are several subspecies and many hybrids of this species, which accounts for the great variety of color and pattern seen in this fish. Behavior within any of the varieties can range from peaceful to aggressive, with the largest of the males usually being the most aggressive. One interesting feature of this livebearer is the apparent ability of the female to change sex and become a male. I have been unable to locate any accounts of females giving birth and then changing to a male. It's easy to identify a male swordtail by the sword-shaped extension of the tail fin, and the modified anal fin known as a gonopodium.
Males are generally smaller than females.
The male appears larger because the tail and sword can often be as long as the rest of the body. Basic care of the swordtail is easy to provide if the aquarium is sufficiently large. Although the swordtail will live in a small aquarium of 10 gallons, it is not particularly suited to the cramped quarters and will seldom breed in this confined space. Most births that take place in these small aquariums began several weeks earlier when the female was in a larger tank. Once the eggs are fertilized it takes from four to six weeks for the first batch of babies to appear.