Telling the sex of a Platy

Telling the sex of a platy is very easy. and can be determined in the following foolproof way.

 
If you examine the diagram above, you will notice that the anal fin of the male platy (the fin circled in red) looks different from that of the female platy (also circled in red). 

The anal fin of the male platy is called a gonopodium.

The anal fin of the female platy, on the other hand, is noticeably more fan shaped.

And that’s all there is to it! That’s how you can tell the sex of your platy.