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my wife saw some sword tails in the store and fell in love with the idea of breeding them but we do not know how to tell the males from the females any help would be gratefull.
 

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Easiest way to tell swordfish apart: male have a long "swordlike" extension on their tales. The female do not. There are some swordtails called lyre tail that have the tail extend on the top and bottom. Also in the lighter females you can look for a gravid spot. This looks like a dark spot close to were their anal fin is. Hope this helps.
 

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Rather than distinguishing it through the other fins, Joe's pic clearly shows a male. Males have pointed fin near their anus which is a sperm depositor called gonopodium.
Females have a triangular shaped fin near their anus.
Males with long and feathery gonopodiums are considered sterile as their long gonopodiums cannot reach the female's vent.
 
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