• Post category:Fish
  • Post comments:0 Comments

Molly fish is an easy to keep aquarium fish that has a high productivity rate, and they come in a wide range of shapes and colors. It is easy to distinguish between the male and female molly, and therefore, in case you have a male and a female in your aquarium, you will witness the difference in colors, shapes, and behavior. Some aquarists love keeping this species and breed them to increase their number. Therefore if you are an aquarist with such intention, you need to ensure that you have the right ratio of males to females.

However, you need to understand how to identify a male from a female to be able to manage their count, especially in a community tank. In this guide, we are going to discuss in detail some of the ways in which you can be able to define a male from a female.

The males and female mollies can be identified using some of their physical features, such as analyzing their colors. Size, shape, and behaviors. Also, their fins, especially the anal and dorsal, play a major role in this process of identifying the male and female. Some of the factors that can be used to identify the difference include;



The mollies are in different colors since they have different species. However, it is important to understand that every color in every species helps you identify the gender of the mollies. In males, you will find brighter and more definite color patterns in male mollies than in females. Also, they have a bolder color display on their fins too. This vibrant color of this species is very attractive, and it can be noticed easily in the tank since it is outstanding.

When it comes to the females, their color seems to be a bit duller and soft compared to the males. If you keep them in the smaller tank with males unknowingly, the color of the female gets overshadowed by the males certainly.


On matters to do with the body size and shape of the mollies, you might assume that they are the same, but that is not right. However, the females have a heavier body compared to the males; their stomach is rounded, and this makes them look somewhat large. During the breeding season, the belly becomes more rounded and enlarges than usual so as to accommodate the young ones.

The extent to which the body of the female mollies grows is dependent on the species type. Generally, females will grow a bit larger than males due to their body shape. The body of the male molly is usually smooth and thinner. These species have a flat stomach area but this can only change if the fish is infected by a disease.  They grow to an average size of 2 to 5 inches in length, and this depends on the type of species.


If you ignore the size of the tail fin, it is pretty similar to both the male and female. This is, however, is the natural result of a larger body overall, and therefore, we cannot really consider it as a meaningful difference. However, it is a different story when it comes to the dorsal fin. The males have larger and longer dorsal fins compared to the females. In most cases, the dorsal fin of the females is 3 to 4 times larger than that of the females, and therefore, there is no way you will not see so the difference.

The male mollies appear larger and more intimidating towards other males as a result of the dorsal fin. With the intimidating look, the fish helps the male to win most of the battles before they even start since the opponent will be scared. Also, the male uses the size of their dorsal fin to their advantage, especially when they are trying to impress them. During the breeding season, as the female chooses the mate, they also consider the size of the male dorsal fin, among other things. Therefore, we can conclude that the size of the dorsal fin matter when it comes to mollies.


The anal fin is one of the details that you need to consider when determining whether your molly is male or female. The anal fin is one of the parts of the body of a molly that you can sit underneath, between the tails and pectoral fins following the stomach area. In the males, you will find a larger anal fin compared to the females. The anal fin changes the model into a structure that resembles the tube and is known as Gonopodium. Through this, they copulate with the female molly fish.

The female, however, has the anal fin having a triangular shape. The color and shapes of the mollies may be different according to the species, but their anal din is the specific part of their body that clarifies gender without any dilemmas.


If you are not lucky to tell the difference between the male and female molly before getting pregnant, it is time to tell. The gravid spot is the female-specific phenomenon that consists of darker coloration that is visible in the belly of the female. This spot appears in the lower portion of the abdomen towards the cloaca, and this usually happens about halfway through the pregnancy. This is approximately two weeks in it.

This phenomenon usually happens to the live bearers, and it is the most common indicator of the gender of the fish since it is only the females that can get pregnant. As an aquarist, you should expect this spot to grow in both size and intensity as the pregnancy heads toward the end, and at this time, it becomes darker. Some keepers of the molly claim that you can even differentiate the fry eyes in the same region when the female is almost delivering.


The mollies are peaceful and easy-going friendly fish that are an ideal choice for a community tank. However, they sometimes display some violence towards one another. Mollies can tell the difference between the members of their own species and the rest, and this causes the males to display targeted violence towards other male mollies. The main reason that leads to that is generally reproductive competition.

 The molly fish usually mate every month, and this means that the male species are always in reproductive competition, more so when the ratio of the male and females is not balanced. It is advisable to keep at least three females for every male molly, and this will reduce the aggression that is caused by males as they compete for the few females. The male mollies will naturally fish for other things like food, space, and sometimes for just dominance.

To be able to control this aggressive behavior between males, you can do so by adding some plants and decorations to the tank. This will break the line of sight between the fighting fish, and the attacked will have a place to hide from the aggressors. On the female part, they are generally peaceful, and you will not find them in any kind of conflict. However, when they are pregnant and are almost delivering, they can become cranky.


There are some aquarists that have been speculating that it is possible to change the gender of the molly. That is not true, and there is no scientific evidence showing that this can be done. All that is available is anecdotal evidence of some people claiming that they have seen their female mollies becoming males at some point. The current scientific consensus defines that mollies cannot change their gender since their gender is genetically defined, which the same case for human beings is.

Some of the mollies appear like they have changed gender as a result of delayed male development, and this can happen under certain circumstances.


The juvenile mollies begin to display some gender differences t the age of  4 to 6 months. However, this is not the final become; some of the late bloomers can go beyond this age before they can display them. Some of the males will mature later compared to others, gaining their male-specific characteristics when they are eight months old or even older. As an aquarist, if you expect to be able to tell between a male and female fry at birth, then you are mistaken. That will not happen until they are of age.

However, the mollies should be separated according to gender after they have established their genders. The ratio should be one male to three or four females for optimal population dynamics.


At this point, you have least the different ways of identifying the males and female mollies, and in this section, we are discussing the importance of defining the males from the females. They include;


 The main reason for identifying the male from female is to manage their ratio in the tank. Once you have correctly identified the number of males and females, you can be able to keep them in a suitable group count. Always, the number of males should be less than females in the group. For instance, if you keep a group of 5 to 6 mollies, it is advisable to keep just one male molly. You can also choose to go with two male mollies, but you need to ensure the tank size is larger enough to avoid fights and confrontations.

 However, it is advisable to always avoid putting more than one male molly in the same tank, and whenever you find them in the same tank, please separate them immediately. To avoid making mistakes and plan for the ratio of males to females, it is important to identify them first.


When you have identified the male and female mollies and put them in the right ratio, you will have avoided aggression in the tank. This is because there will be less number of male mollies in the same group, and there will be no fight for dominance or competition for the females. The males love to have less competition when it comes to finding mating mates, and therefore with more males, it increases the competition, something they will fight to eliminate. It is therefore important to identify the gender correctly to avoid putting males in the same tank and causing fights.


For proper breeding to happen, the gender of the mollies must be identified correctly. When you have correctly identified the gender of a certain molly, you will be able to pair them right as you prepare them for breeding. However, if you do not identify the right, you will end up failing during breeding. You will find yourself having a males only tank, and there will be no breeding at the end. You should therefore put a lot of emphasis on identifying the right gender if you want to succeed in inbreeding.


Can Female mollies have babies without males?

It is possible for a female molly to store the male sperms for months after mating, and later she will give birth to all babies once without necessarily having the male in the aquarium. This means that she can give birth to a young one without male mollies being near, but that does not mean that she can give birth without mating with the male molly.

Can I keep female mollies together?

 Yes, you can keep female mollies in the same tank since they are not aggressive to each other. There will be no problem, but they might sometimes end up chasing one another as there will be a pecking order. If you note that your females are chasing each other and it is getting worse with time, you should separate them immediately.

Do female mollies become aggressive during pregnancy?

 Yes, during the pregnancy, the female mollies get aggressive. However, the aggression is usually temporally and will end after the pregnancy period.


As you have read from this guide, it is important to identify the gender of the molly before putting them in a group because that will be important in maintaining the right ratio. If they are kept in the right ratio, they will live happily and will even be healthier since they will not be stressed. We have studied some of the factors you can use to differentiate between male and female mollies, such as shape, color, and size.

However, it is not only about differentiating; you need to do it correctly because any mistake in the process means you will affect everything. Pay attention to every detail as you identify them, and you will have happy and thriving mollies in your pond or tank. Take your time, and if you do it correctly, you will never regret it.

Leave a Reply