How to Tell If a Swordtail Is Mating?

Swordtails are small fresh/brackish water fish found in southern Mexico and Central America. They are a popular aquarium fish and are bred in captivity to produce different colors and varieties. Swordtails live in brackish environments in nature, but can be kept in freshwater tanks. They are tolerant of a range of temperatures and prefer a pH between 6.8 and 7.8. Swordtails are livebearers, so a female gives birth to fry rather than releasing eggs to be fertilized externally.

Things You'll Need

  • Fresh or brackish water aquarium
  • Swordtail fish
  • Live plants
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Instructions

  1. Swordtail Anatomy and Mating Conditions

    • 1
      Some freshwater fish are compatible with swordtails.

      Observe the anatomy of the swordtails to distinguish between the sexes. Male swordtails have a "sword" that extends from the anterior portion of the tail. Females are similar in size, color and appearance, but lack the sword.

    • 2
      Adding aquatic plants provides hiding places.

      Adjust tank conditions to facilitate mating. Male livebearers often harass females, so it is best to adjust the sex ratio to two to three females per male. Add live plants to the tank to provide hiding places for the females. The tank temperature should be 72 to 79 degrees. To encourage mating, increase the tank temperature two to three degrees. Breeding will occur naturally, even in a community tank.

    • 3
      Swordtails are fast swimmers.

      Observe fish for mating behavior. Mating is often quick and difficult to observe directly. The male's anal fin is modified into an organ called the gonopodium. This is used to inseminate the female. The male will chase the female, nipping at her occasionally. Once he corners the female, he will swim backwards at her and attempt to insert his gonopodium. If the act of mating is not observed, wait for two or three weeks to look for signs of pregnancy in the females.

    • 4
      Adults may eat the newly released fry.

      Observe the female swordtail in the tank. If her abdomen is dark and rounded, she is carrying fry. The dark spots are the eyes of the fry. Adults will eat fry, so separate them as soon as they are released and place them into a separate tank.