The Courtship & Mating Habits of the Tropical Swordtail Fish

Swordtails are tropical fish species notable for their striking colors, various tail types and peaceful behavior. Successful breeding of swordtails relies on an understanding of their courtship and mating habits. Courtship, mating, gestation and then birth are some of the most exciting experiences for fish keepers. It is interesting to observe a pregnant female swordtail give birth to free-swimming offspring.

  1. Origin

    • Wild swordtails are found in waters from southern Mexico to Guatemala. They live in slow moving streams and ponds. The name derives from the sword-like appearance of the male's caudal fin, an elongated spike located on the underside of the fish and pointing away from the body toward the rear. Studies in Mexico have determined that male swordtails in the wild use chemicals in their urine to court female swordtails.

    Sexing Swordtails

    • Male and female swordtails are easily recognizable due to tail shape, as the female is without the elongated tail. Female swordtails measure approximately three inches and are rounder than the male. She has a fan shaped anal fin. Male swordtails have a long and tubular pelvic fin that is used for mating. The male fish are territorial and aggressive when kept in a tank where the males outnumber the females.

    Courtship and Mating

    • Swordtail fish become sexually active as early as three months of age. When trying to mate, the male fish will chase and exhaust a female, attempting to impregnate her with his pelvic fin. Some of the male's sperm immediately fertilizes some of the eggs present inside the female. The rest remains in her ovarian tubes, and may allow her to give birth six to nine times in her life.

    Gestation Period and Birth

    • The gestation period averages from 30 to 40 days. A dark spot in the front of the female's anal fin will become noticeable while the eggs grow inside the female. During birth, the young swordtails break out of the egg and are able to swim freely. Swordtails bear live young, which they will eat if given the chance. Keep pregnant females in individual holding tanks or breeding traps. The first brood will produce approximately fifteen offspring. This number will increase with each successive brood.