Are Molly Fish Aggressive Or Friendly?

Can Molly Fish fight?

Are Molly Fish Aggressive Or Friendly?7 mins read

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Tal Halperin
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Are molly fish aggressive or friendly?

When setting up a molly fish tank, you may wonder ‘are molly fish aggressive?’. After all, it’s natural to want your fish to get on, and you may have other tankmates in mind.

After hearing mixed reports about their behavior, or others’ bad experiences, it can be hard to tell if you’re wondering are mollies aggressive. In truth, these are friendly fish, but as with any species, it’s always best to fully understand them fully.

This guide will answer the common question ‘are mollies aggressive fish’ and show you how aggression may arise in circumstances of competition or stress, what you can do about it, and how to set up a peaceful community tank with Molly Fish – so read on.

Are Molly Fish Aggressive Or Friendly?

Are molly fish aggressive or friendly?
Molly Fish differ from other species in that they are live-bearers, meaning they give birth to live young. You may find yourself asking ‘Are Molly Fish aggressive or friendly?’

Molly Fish differ from other species in that they are live-bearers, meaning they give birth to live young. You may find yourself asking ‘are mollies aggressive’ after this, and wondering what other unique requirements they have.

In pet shops, you may even see them kept alongside other species like Platies, Guppies, and Swordtails. This is just one example of how Molly Fish are a friendly and peaceful species, but like with any fish, aggression can happen over food, mates, or living space.

Are Mollies Aggressive Over Territory?

You may wonder are molly fish aggressive over territory or food? If you have seen Molly Fish kept in an overcrowded tank, you will often see them chasing each other or vying for territory. However, given enough space, Molly Fish should not be aggressive at all. In fact, they are actually very friendly. As a result, many fish keepers recommend them as a tank mate for other tropical freshwater species. However, they do need a tank of a minimum of 30 US Gallons or 114 liters.

What Makes Molly Fish So Friendly?

So, we have established that Mollies are a friendly species without any inherent aggression. This is especially in comparison with hierarchical species like Angelfish. But what makes these guys so friendly?

As live-breeding fish, Mollies are often trying to win a mate. This means they are social fish, and these social shoal dynamics mean they prefer the company of other fish. They are not solitary or territorial at all, unlike species such as Betta Fish – although they can act as good Betta tankmates if other conditions are right.

However, once in a familiar group, other factors can lead to Mollies becoming more aggressive than they would be with unfamiliar fish. So if you want to know ‘are mollies aggressive’ it’s important to look at the tank dynamics. In the end, like with any community tank, you will quickly get to know the dynamics of your individual group of fish and what is and is not normal behavior for them.

In addition, as small fish that are often prey in the wild, Mollies prefer safety in numbers and are happiest hanging out in groups of six plus. This means that they have evolved to tolerate the presence of other fish, and indeed, they even require this.

Author’s Note: As social fish, Mollies’ group behavior is complex. There are many things scientists still do not know about their social relationships. However, one thing is certain, which is that your Mollies need others of their own species to truly thrive.

What Tankmates Are Molly Fish Compatible With?

What tankmates are molly fish compatible with?
The biggest concern is that Molly Fish can become prey for larger fish like Cichlids.

Once knowing these are friendly fish, don’t be too fast to integrate them into a community tank, like any fish, there are tankmates that they are and aren’t compatible with.

The biggest concern is that Molly Fish can become prey for larger fish like Cichlids. The fact of the matter that far from wondering ‘are mollies aggressive fish’, these guys are often actually prey that can’t fight back. The exceptions with cichlid aggression are Angelfish and Discus Fish. These fish are too small to feed on Mollies and can be suitable tankmates if you meet other requirements of both species.

Mollies also don’t get on well with coldwater species like Goldfish, simply because the water temperatures are incompatible.

Molly tankmates are otherwise very varied. The following list will give you a good idea of which fish they can get on with. You may wonder are molly fish aggressive to smaller tankmates? Generally, the answer is no.

However, you must remember other conditions like tank size and correct food are still important. This list does not imply these fish have the same needs at all, only that they generally will not trouble each other if kept together.

Best Compatible Molly Fish Tankmates:

  • Angelfish
  • Discuss fish
  • Swordtails
  • Chinese Algae Eater
  • Platies
  • Rasboras
  • Tetras
  • Pleco Fish
  • Small loaches such as the Kuhli Loach
  • Swordtails
  • Platies
  • Guppies
  • Smaller Cichlids such as the Electric Blue Ram Cichlid

Are Molly Fish Friendly To All Other Species?

Yes, generally Molly Fish are friendly to most other species. There is only one exception, and even then, this is not a common occurrence, but aggression in the form of fin nipping may occur towards similar, closely related fish like guppies, as male Mollies may see these as competition for mates.

Author’s Note: You can solve this easily by choosing the correct sex ratio and giving your fish enough space. It is far more likely that Mollies, as peaceful fish, will receive aggression from larger species, especially cichlids, so choose these carefully.

What Are Some Circumstances In Which Molly Fish May Show Aggression?

What fish cannot live with Mollies?
As Molly Fish are so friendly to other species, you can forgive yourself for thinking that they are also this friendly to their own kind.

As Molly Fish are so friendly to other species, you can forgive yourself for thinking that they are also this friendly to their own kind. And yes, Mollies can coexist in schools. But when it comes to breeding, things are sometimes different. The answer to ‘are molly fish aggressive when breeding’ is complex. So, read on to understand when and why Mollies might show aggression.

Lack Of Space

It may seem obvious, but any fish living in unsuitable conditions that are too small will show aggression. This is because fish will feel threatened due to competing for territory and food. Mollies can grow surprisingly large, up to around 4 inches or 10 cm.

You should keep mollies in groups of five or 6. Generally, are mollies aggressive in smaller or larger groups? Not necessarily, but it does increase the likelihood. Either way, for a group this size a tank of ideally 30 gallons or 114 liters at minimum is ideal for them to properly thrive.

You may also wonder ‘are mollies aggressive fish when alone?’. Again, not necessarily, but keeping a single fish will dramatically increase its stress level. This can lead to aggression down the line.

Author’s Note: When planting your tank you can create separate territories by spacing plants in groups, providing pathways and hideaways, and adding driftwood and rocks to break up the area.


So, are molly fish aggressive when breeding? Breeding is one of the occasions that Molly Fish can and do show aggression to their own species. These fish are prolific breeders and often males will harass females into breeding with them. This is called ‘sneak’ courtship. Generally, it is a strategy of smaller and less sexually desirable males. In fact, it can sometimes happen even when a female Molly is already pregnant.

Even if not overtly aggressive, this can be intimidating and stressful for your female Mollies. As a result, you should add a sex ratio so that there are one or two males for every three to four females. That means no one female receives too much harassment.

Are Mollies Aggressive Fish When Breeding?

Apart from this, Mollies are not seriously aggressive when breeding, unlike bettas, although they can show some behavior that looks aggressive. The actual native process can look like chasing, and thus you may worry that your fish are being aggressive. In addition, fish may chase each other simply as a form of play.

How To Deal With Aggression In Molly Fish

The best way of dealing with aggression in Molly Fish is to find the cause and remove it. Generally, this is caused by a less-than-ideal sex ratio, poor water conditions, or a lack of space. In the latter case or the first case, you may have to find a bigger tank or add more fish respectively.

Author’s Note: Sometimes fish aggression can break out just because fish feel stress due to dirty water. Always remember to clean your Molly tank once a week. Replace about a third of the water with fresh by removing it with an aquarium vacuum. Then, pour in clean filtered water of the same temperature.

Ensuring Your Molly Fish Remain Friendly

Ensuring your molly fish remain friendly
mollies are generally peaceable naturally you want to ensure your Molly Fish group remains calm and friendly.

Although they are generally peaceable naturally you want to ensure your Molly Fish group remains calm and friendly. To do this, simply ensure you meet all Molly Fish care requirements and they get the best conditions possible:

Feed Them Regularly

Always feed your fish regularly! It goes without saying, but fish that lack food are more likely to become aggressive and fight over food when you do provide it.

Mollies are omnivores and tropical fish pellets or flakes can work as basic food, but they always enjoy you enriching their diet with fresh or frozen protein like bloodworms, brine shrimp, and daphnia.

Keep The Tank Clean

Keeping the tank clean ensures Molly Fish won’t experience too much stress, or be susceptible to disease. If a fish is in pain or feels threatened it may become aggressive.

Use A Large Enough Tank

Overcrowding is a very common cause of aggression in Molly Fish. In addition, it can exacerbate the pre-existing behaviors male Molly Fish have of chasing females. This is because, in close proximity, there is very little opportunity for the female Mollies to get away.

Thus, a large enough tank is crucial for providing a harmonious balance.

Provide Different Territories

In addition, if more aggressive tankmates are picking on your molly fish, you may initially panic. However, one way to manage this is to provide them with hiding spots or separate territories in the tank. This is not just a solution but can also be a preventative measure.

Different territories mean your fish will not feel the need to fight each other. They also provide spaces for shy fish or pregnant females.

Bottom Line

Molly Fish
You should rarely have aggression issues with this friendly fish, which makes a great tankmate for a huge variety of popular aquarium fish species.

You should rarely have aggression issues with this friendly fish, which makes a great tankmate for a huge variety of popular aquarium fish species. If you’re wondering ‘are molly fish aggressive?’ rest assured they are great for beginners. However, if aggression does break out, hopefully, this guide will break down why and what you can do about it.

Remember, getting conditions right is three-quarters of the answer. Any fish, when kept in the right environment, will show calmer and more natural behavior than those that are not – so take care of your fish, and they will reward you for it.

Frequently Asked Questions

Are Mollies aggressive fish to other tankmates?
Whether Molly Fish are aggressive to other tankmates versus their own kind tends to depend on the individual environment, but two factors can greatly influence this: fish stress levels, and the amount of space. Closely connected, stressed fish are more likely to be aggressive towards both their own kind and even compatible tank mates. Likewise, fish with little space will see all other fish, the same species or otherwise, as a threat.
Can Molly Fish fight?
Molly Fish can indeed fight, though it is important to recognize this behavior to differentiate it from breeding and courtship. Molly Fish courtship, like that of other livebearers, can be quick and occasionally look aggressive as a result of this. However, real aggression and fighting will involve nipping and chasing behavior, especially to the fins, without rest. Aggressive fish will occasionally attempt to corner other fish. If aggression gets too serious, it is important to move the fish to a spare tank.
Are male Mollies more aggressive?
There isn’t a huge amount of difference in male and female Molly Fish aggression. Female fish can easily become aggressive in times of overcrowding. However, the one difference is male Molly Fish can indeed aggressively mate with the females by ‘sneak’ courtship and this can become a stressful occurrence, so keep your sex ratio with more females than males (about twice as many) to ensure your female Mollies do not get harassed.
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Sydney Perry

Sydney Perry has loved fish since she was a child and has enjoyed keeping many varieties over the years, ranging from black moors and shubunkins to betta fish. As a lover of nature and of Japanese culture, her dream tank is an Iwagumi aquascape, combining fish with carefully crafted aquatic landscapes in miniature.