How to Determine Molly Fish Gender?

How to Determine Molly Fish Gender?

It is important to know the sex of your molly fish, as this can help to avoid aggression and allow you to create a more balanced aquarium.

Distinguishing them by appearance and behavior is the most reliable way to tell males and females apart.

Male mollies, for example, will get violent with one another in crowded tanks or when there are not enough females available.

In this guide, we will discuss everything you need to know about how to determine the gender of your molly fish.

How to Sex Molly Fish by Appearance?

The female molly fish is generally larger than the male and has a rounded belly, while the male is slimmer with a pointed abdomen.

However, this may not be the case with all molly fish, as some males can also have a rounded belly due to some diseases. Here are some more tips on how to tell them apart by appearance:

Point of DifferentiationMale Physical CharacteristicsFemale Physical Characteristics
Body ShapeThe males are even skinnier, shorter, and more compact.Female mollies grow larger than males.Aside from that, female mollies have bigger bellies as a result of their uterus.
SizeBetween 2.5-3.5 inchesUp to 5 inches
Tail Fin ShapeThe males’ dorsal fins are significantly larger and more extensive than those of the females.In most cases, the males’ dorsal fin is three to four times larger than that of females.The female molly fish’s dorsal fin is shorter and blunter when compared to the male’s.
Anal Fin ShapeThe male possesses a thorn-shaped fin that never expands wide, similar to the case with females. That’s because the male’s anal fin is in fact a gonopodium, which are copulatory organs that they will employ to deposit sperm inside the females during mating. It is always slender and thin with a pointed tip.The female mollies have bigger and more numerous anal fins that flit about freely in the water as they swim.
Gravid SpotMales do not have a gravid spot.The gravid spot is a female-specific phenomenon that results in a darker coloration visible in the belly of the female. It will appear in the lower part of the abdomen, near the cloaca, around halfway through gestation (around 14 days).
ColorMale mollies tend to acquire brighter and bolder colors than female mollies.This attracts female mollies towards mating.The colors of female mollies are dull, Timid, and Demure.

How to Sex Molly Fish by Behavior?

In short words, their aggressive behavior. Male mollies can become aggressive when there are not enough females around or when the tank is too crowded while female mollies are typically not as aggressive.

Some other behavioral cues can help you determine the sex of your molly fish:

Mating Behavior

Mollies mate every month, which means males are almost continuously in reproductive competition, especially when there aren’t enough females.

To breed molly fish, male molly attempts to attract female molly’s attention in many different ways. They chase females and swim in front of them, revealing their fins to get their attention.

On the other hand, females are more docile and avoid confrontation making it easier for you to identify them.

So, you can easily find out the gender of your molly fish by their behavioral cues. If they are engaging in reproductive behaviors, then they are most likely male.

Dominance Behavior

Male mollies are also more likely to be dominant over others in the tank, including both males and females.

You can witness them squabbling over food, territory, and even for no other reason than pure male-male dominance.

When Can You Tell the Gender of Molly Fry?

Mollies will begin to exhibit distinct sexual distinctions between 4 and 6 months of age.

However, these are not absolute timescales because certain mollies are known as late blossoms.

The term is used in many species of livebearers, as well as fish in general. Some males will mature later than others and develop male-specific characteristics after 8 months old or even older.

That being said, once you know what to look for, you must split them up based on their sex. For optimum population dynamics, keep one male for every three or four females.

Last Words

If you are a beginner aquarist, do not worry if you cannot immediately identify the gender of your molly fish. By following the guide, you will quickly learn how to do that.

We hope this guide was helpful and informative. If you have any questions or suggestions, please leave us a comment below. Happy fishkeeping!

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