Can Mollies Change Gender?

If you are an enthusiast about mollies and tend to collect them in your aquarium, you might have noticed some of them changing their gender.

Let me assure you, mollies don’t and can’t change their gender, but it can seem as though for multiple reasons. You may observe your female molly fish suddenly showing male characteristics and believe that she had changed genders, when in fact, your molly fish was a male from the very first beginning. 

For more clarification regarding this misjudgment, keep on reading this article.

Can Mollies Change Gender?

Molly fish may show different gender characteristics all of a sudden. These instances aren’t proof of gender change in molly fish. On the contrary, they help prove that mollies can’t change genders at all.

A closeup of a black and gold molly swimming in an aquarium under the lights

These situations are caused by two factors that can be explained as follows:

Females In Menopause

Not literal menopause, obviously, but a few aquarists declared that their very old female mollies started to grow a gonopodium at some point and even showed male attitude. They suspected their molly was a male and wondered whether their mollies could change genders.

However, this can only signify females getting old, not changing genders. What supports this is that there is no verified proof that these females can produce sperm to mate with another female after that drastic change.

To prove that this female molly fish is, in fact, a male, we would need to isolate a virgin female molly along with it to see if this younger female would get pregnant. However, so far, this is not scientifically proven.

Late Blooming Males

Sometimes, there are instances when your female molly fish is slowly turning into a male, chasing after other females and impregnating them as well as completely changing her physical character.

In that case, your molly fish was never even a female in the first place; you molly was just a late-developing male. Late development is a genetic trait that is scientifically proven and is common in aqua life.

Therefore, younger male molly fish can be mistaken for a female since they all look similar.

How To Identify a Molly Fish’s Gender

If you’re trying to identify whether your molly is a female or a male, you can do this by noticing a few signs and features. First, however, make sure that your molly fish is mature enough to display their gender.

The most important signs and features that you should be looking for in your molly to identify their gender include:


One thing you can look for to identify your molly’s gender is their color. The male mollies mostly have a more vibrant color, while the female mollies have a dull and faded color.

For instance, in black mollies, males tend to have a rich charcoal color, while the females have a more faded brown or an orange undertone.

In the gold dust molly, the male has an intense and pigmented orange color, while the female’s color is more of a pastel shade.

The reason for this color difference is that the bold colors of male mollies make it easier for them to attract females for mating.


Female mollies are usually wider than male mollies due to their large bellies. Since they are livebearers, a healthy female molly would have a big, lumpy belly to be able to give birth to an average of 80 fries.

Female molly fish have more rounded abdomens, while the males have flat ones. It is also a bit easy to determine the gender of a male molly since they have a torpedo-shaped body.

Male mollies always have flat bellies unless they are infected by any disease. Male mollies can also grow from 2 to 5 inches long, depending on their type of species.

Dorsal Fin

The dorsal fin is the back fin you can find visible in your molly fish. Yes, males and females both have it. However, the male’s dorsal fin is larger than that of the females.

That large size of their dorsal fin helps them appear more attractive to the female mollies so that they can breed.

Anal Fin

The anal fin is the area of the molly’s body that can be seen beneath the pectoral fins and tails, following the stomach. Males’ anal fins are often bigger or longer than females’.

The males’ anal fin evolves into a tube-like structure, which is known as gonopodium that serves as a copulatory organ to mate with females.

For females, their anal fins look triangular, making them an easy way to identify a molly’s gender.


In mollies, you can be sure that the one that’s always swimming around the females trying to catch their attention is a male. It’s because they think if they followed the female around long enough, they’d be able to mate with her.

Not only that the male molly fish are attention seekers, but they also tend to be more aggressive. This can be a result of a lack of breeding or because there are too many males in the same tank, and they’re trying to assert their dominance.

Females, on the other hand, are less aggressive than males. However, they still get a little offensive if they are sick or getting through their pregnancy phase.

The Importance of Identifying Your Molly’s Gender

Now that you know how to tell whether your molly fish is a female or a male, are you wondering why this information is significant to you?

Well, knowing your molly’s gender is important for a couple of reasons:

Male to Female Ratio

The most important reason to distinguish between male and female molly fish is to keep the tank’s proper ratio. It is crucial that you make sure that you have a ratio of 2-3 female mollies per male.

Never keep a female alone with two male molly fish. This will cause the males to be extra aggressive and fight with each other to win the female’s approval, and in the process, the female could get hurt as well.


In order to breed your molly fish correctly, you must know their genders. Otherwise, you would have too many males or too many females. Some people would even keep a tank full of only male or female molly fish.


Your molly fish didn’t suddenly change genders; it’s just showing its actual characteristics. Changing genders isn’t scientifically proven among molly fish. Therefore, rest assured knowing that as long as you’re able to correctly identify your molly’s gender, it will not change overnight.