How To Sex Livebearers
One of the first questions hobbyists ask when they purchase a Livebearer is "How do I sex a
Molly/Swordtail/Platy/Guppy?"  This is often upon learning just how prolific these fish are.  Most female  
Livebearers purchased in stores are already carrying fry {babies}.

The Poecilidae family includes Mollies, Guppies, Platies, and Swordtails, as well as other less
frequently seen fish, such as Limias.  Poecilidae Livebearers are a relatively easy fish to identify as
male or female.  The female has a dark or red Gravid Spot just above and forward of her anal fin, directly
behind her stomach.  This is where the fry will grow and develop.  It may be small or larger if she is
already carrying fry.  The spot will grow as the babies grow, until the female gives birth.  If the fish is dark
or opaque in color, it may be more difficult to see the Gravid Spot.

The male Livebearers in this family are equally easy to identify once they are juveniles, although some
males do develop later.  The males have a modified anal fin called a Gonopodium.  This fin is detached
from the body to allow for movement so he is able to inseminate the female.

You can often watch a tank of Livebearers to differentiate between the males and the females.  The
males are determined breeders who will constantly be chasing the females.  The male Livebearer will
often perform an elaborate display of finnage and dance to attract the female.  He will also attempt to
position himself beside her for insemination.  However, males will often display similarly when
challenging other males so this method is far from reliable.  Males also will often have more elaborate
finnage, sometimes more vivid coloring and the female is usually larger than the male.  Due to the
incessant attempts to breed by the males, at least two females for each male is recommended to
prevent female stress.
Content and original photos:  Copyright © 2006 - Pacific Aquatics Ltd. All Rights Reserved