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The Difference in Male & Female Swordtail Fish

| Updated October 19, 2017

Swordtails are a popular and beautiful breed of freshwater aquarium fish. They are named for a pointed extension which grows off the back of their tail fin. There are several differences between male and female swordtails.

Telling Males From Females

Only male swordtails have the tail fin extension. Females have a rounded tail fin. Females' bodies are also more rounded, fuller and about one-half-inch longer at maturity.


It is important to determine the sex of your swordtails, and separate males from females if you do not wish them to breed. They can reproduce from as early as 12 weeks old.


If you are keeping males and females together, have two to three females per male. The males chase the females around attempting to mate with them: if there are more males than females, the females will get no rest.

The Sword

The sword has no actual function, it is decorative. Swordtails have been selectively bred for decades to produce various colorings, shapes, and sizes. Among the most popular are vivid reds and oranges and glowing greens. Whatever color the fish is, the sword usually has a black band along the bottom edge.

Fun Fact

Swordtails can interbreed with another fish species, Platies.