how do you tell male mollies and female mollies apart?

Question

I have two mollies but we don't konw the sex.

both are black all black but one is fat:|

Answer 1

Mollies are live bearing fish. And all freshwater, live-bearing fish have a simple trick to determine their sex. Look at the anal fin (the single fin located on the underbelly, on the back-half of the fish) and dorsal fin (the big one on their back).

Male mollies have a spike-like anal fin pointing towards the rear. The males are usually a little bigger in size and have a more decorative and larger dorsal fin. Females have triangle or fan-shape anal fin that hangs down. They are usually smaller and have small, plain dorsal fins.

The picture on this page is of a black female molly: http://www.liveaquaria.com/product/detailed_image.cfm?pCatId=2089

I hope this helps!

Answer 2

As stated else where the males has a pointed anal fin, and the female a rounded anal fin. Males will have bigger showy colors and sails (top fin). Molly who are knocked up get big belly, and will show an eye spot. (Can't see on black molly.) A female can give birth 3-4 times without a male.

Answer 3

male are bit smaller than a female, very bright in colour and always running after females.

Answer 4

The males have a penis It looks like a slinder fin by the anus.

Answer 5

Males have colorful tails. Females are more plain. (poor girls)