I'm not that good at these frogs yet, so I can't sctually sex the one in the picture.
But I know that the males have something called "post axillary subdermal gland" behind every armpit. It looks like a small bumb that can be white or pinkish in color.
Females have a cloaca between their legs.
Check out this site for more info
http://aquaticfrogs.tripod.com/id15.html
Hope it helped
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