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FAQ on Breeding Livebearers
by Ruby Bayan

Swordtail I share the fondness for livebearers with a lot of tropical fish hobbyists. I would imagine we all love to see little baby fishes being born fully-formed, alive, and swimming. It's certainly a joy to witness the miracle of life happen in your own aquarium!

Here's a FAQ (frequently asked questions) sheet I've prepared to answer the basic concerns about breeding livebearers.

Q: How many male and female livebearers would be good and healthy together in an average-sized tank?

A: Livebearers are especially gregarious -- adult males constantly follow, harass, and mate with females. Therefore, in order to keep the females healthy and not too stressed from the advances of the male, the ideal combination is two females to every male.

Q: How soon do livebearers become mature enough to breed?

A: Most livebearers mature at an average of four months. Therefore, about four months after birth, they are ready to have their own babies.

Q: How can I tell the male from the female?

A: The nice thing about livebearers is that males have a "sex organ" called the gonopodium. It's a specialized fin protruding from the underside of the fish, and if you look closely, males can direct the gonopodium towards the female in the act of courtship. The gonopodium serves as a tube that transmits the sperm into the female. In the female, this ventral fin is fan-shaped.

Male Fantail Guppies

Male Guppies are smaller, more colorful, and the fancy ones have extended fins compared to the female. Male Swordtails have longer swords, some females don't have swords at all. Male Mollies and Platys are smaller and slimmer than the females.

Q: How can I tell if a female is pregnant?

A: Livebearers are voracious eaters and sometimes their stomachs bulge after a full meal. Pregnant livebearers bulge in the stomach area, and it doesn't subside after feeding time -- it just keeps growing. Light colored livebearers develop an obvious darkening of the skin, called a "gravid spot," right at the anal area. The spot enlarges and grows darker as the pregnancy progresses. It's like a window to the little babies inside.

Q: How do I know when the female is ready to deliver her young?

A: The average gestation (pregnancy) period of livebearers is four weeks. In other words, when you notice that the female is obviously pregnant, you can expect the babies within four weeks. There is really no accurate indication that the female will be dropping her fry within the next 24 hours, but if you note that her gravid spot is already large and dark (you can almost see the little ones inside), and she looks like she's about to explode, you can surmise that delivery will be very soon.

Q: Should I transfer the pregnant female to a breeding tank?

A: A breeding tank will help raise the survival rate of the fry. Once born, the fry risk getting eaten by adults who would immediately see them as tasty live food.

Q: When should I return the female to the community tank?

A: Give her about 6 to 12 hours (from the time the first baby comes out) to drop all her fry, and to take a breather before she has to again deal with the advances of the males in the community tank.

Q: How soon before she gets pregnant again?

A: Sooner than you can say "Geronimo!" Female livebearers are able to retain sperm inside their bodies such that one load can actually account for two to three pregnancies. So, even in the absence of a male, females can continue to deliver fry every five to six weeks. Talk about the miracle of life!

See also: Feeding and Breeding Livebearers

Suggested Reading:

Guppies, Mollies, Platys and Other Live-Bearers: Purchase, Care, Feeding, Diseases, Behavior and a Special Section on Breeding

Mollies: Keeping & Breeding Them in Captivity

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