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5 Easy Ways To Go About Sexing Mollies With Ease!

With so many people getting involved in the fish keeping hobby right now and mollies being an excellent fish to keep for beginners, there has been a huge spike in the popularity of mollies that shows no signs of slowing down anytime soon.

We have noticed an increasing number of questions from the community about keeping mollies in aquariums but they really are a great entry-level fish to keep so the majority of the questions are relatively straightforward.

One of the common questions that we have seen people reaching out and asking about is how to sex mollies to work out if they are male and female.

Once you know how to go about sexing mollies, the process is actually very easy but it is also very important to get right or you end up risking an influx of baby mollies to your aquarium.

Due to this, we have decide to go over the fine main ways that you are able to sex mollies to try and keep your males and females separate if you are not actively trying to breed your mollies.

Although many people new to fish keeping think that it is a great idea to start breeding their fish, you will quickly have to upgrade your aquarium tanks for space and it is often difficult to find a steady buyer for your fish.

Female mollies are able to store sperm too so once they have been bred once, they can product a large number of babies even if you remove them from the male mollies you own too.

How Old Do Mollies Have To Be Before You Can Accurately Tell Their Sex?

Mollies do tend to have to be about the two months of age mark before you are able to sex them due to their early development stages usually focusing on their initial growth.

From the four to eight week point, you are often able to get a good idea as to if your mollies are male or female though.

We just wanted to point that out as we often see people saying that they are unable to sex their mollies but it is often just down to the fish being too young.

We understand that it is very important to try and identify the sex of your mollies as early as possible but you have to keep in mind that mollies generally take around two months to reach sexual maturity anyway.

This usually gives you a period of a couple of a week or two before you have to start worrying about your mollies breeding after you are able to accurately sex them.

Sexing Mollies By Their Anal Fins!

Male mollies tend to have a long, thing anal fine that they will keep tucked against their body where as female mollies have a shorter triangle shaped anal fin that they will usually keep fanned out as they swim.

Looking for the differences in the anal fins of your mollies is usually the quickest and easiest way to accurately sex them due to the differences being obvious.

Another advantage of using this method of sexing your mollies is that the color and patterns of your mollies is not important either.

The colors of some mollies, especially solid colors rather than patterned mollies can sometimes be a pain with some of the other methods we have below to help you tell the sex of your mollies.

You are often able to accurately check the shape of the anal fin of a molly to tell if it is male or female once the fish are a couple of weeks old too.

This is due to it being a physical feature that can sometimes even be identifies when the fish are still just fry helping give you plenty of time to separate your male and female mollies.

“female molly” and “male alpha molly” by h080 is licensed under CC BY-SA 2.0. To view a copy of this license, visit

Sexing Mollies By Their Color!

Sexing mollies by their color and patterns can be an easy way to tell if your mollies are male or female.

Male mollies tend to have much brighter colors with a higher color intensity while also having a more developed, complete-looking pattern too.

This method tends to be more difficult with solid, single-colored mollies but you can often still see the color differences between male and female mollies with ease.

One thing that we would point out is that the diet of your molllies can cause issues with the color development of the fish in some situations. If your mollies are on a low quality food then the colors of the male mollies will often not develop well and make this method of sexing your mollies more difficult.

Feeding your mollies a high-quality mollie fish food is a quick, easy, and cheap way to prevent this problem though and it will also help to keep your mollies as bright and beautiful as possible too.

Sexing Mollies By Their Dorsal Fins!

“female molly” and “male alpha molly” by h080 is licensed under CC BY-SA 2.0. To view a copy of this license, visit

Male mollies have a larger, longer dorsal fin that they will often keep extended where as female mollies will often have a shorter, smaller dorsal fine that they will commonly tuck against their body when not swimming much.

Male mollies over two months of age will often keep their dorsal fins fully extended at all times, especially if they are in a tank with female mollies making it easier to sex your mollies.

This is another method that you are able to use to sex your mollies after around two weeks of age as this is a biological physical feature that will be with the fish from being a fry.

It can be easy to use the dorsal fin and anal fin methods to identify if your mollies are male or female from the age of around two weeks if needed.

Sexing Mollies By Their Size And Shape!

“female molly” and “male alpha molly” by h080 is licensed under CC BY-SA 2.0. To view a copy of this license, visit

Female mollies tend to be larger than male mollies offering another way to sex your mollies and sort the males and females apart.

When looking at the mollies from the front or from above you will often notice than female mollies also have a router body as well as a wider abdomen too.

Although the general larger size of mollies does tend to be much easier to identify in female mollies when compared to males, their larger abdomen can be more difficult to check.

You will often have the best look when looking down on your mollies from above but depending on the activity level of your fish and if they stand out from your substrate of choice, this may still be difficult to do.

Sexing Mollies By Their Behaviour!

Once mollies reach the age of around eight weeks they become sexually mature and the male mollies will start to seek the attention of the females.

They will often chase the female mollies or swim in front of them with their dorsal fin fully extended to try and catch the attention of the female mollies in the tank.

If you are not trying to actively breed your mollies then waiting until this stage to sex them can be problematic as your fish are already sexually mature and may have already mated.

As we mentioned back at the start of the article, female mollies can actually store sperm for long periods of time too resulting in multiple releases of baby fish fry from a single pairing.


That brings our article going over sexing mollies to an end. We hope that we have been able to help our readers better understand how they are able to quickly and easily sex their mollies with ease. Some of the methods covered above will require your mollies to be around the four to eight week mark to be visible but others can be identified once the fish are around the two weeks of age mark.