Are Mollies Schooling Fish? Behavior And Stocking Guide

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If you’re thinking about adding Mollies to your fish tank, you may be wondering whether they swim in schools.

Find out how many Mollies you can maintain in one tank and what other fish get along with them, as well as how Mollies behave when kept in a group, in this comprehensive article.

Behavior Of Molly Fish When Kept As A Group


Molly fish are shoaling fish, meaning they swim in groups. However, it is worth highlighting that they are not strictly schooling fish.

Key HighlightsSchooling FishShoaling Fish
DefinitionFish that swim in groups in a synchronized way.Fish that swim in groups but not necessarily in a coordinated way.
PurposeTo protect themselves from predators.To socialize and find mates along with protection from predators.
ExamplesCory Catfish, Neon TetrasMollies, Guppies

So in other words, being a shoaling fish, mollies are not as socially cohesive as, say, a school of zebra danios or a school of cory catfish, despite the fact that they do swim together.

Molly fish in groups have a lot of social interactions with one another. They swim together and even pursue each other sometimes. Male molly fish tend to swim up to a female in an attempt to mate with her.

In order to lessen the likelihood of aggression towards a single molly, it is important to have the right male to female ratio in the tank – ideally, 3 females for 1 male molly.

One fascinating fact about molly fish is that they are often quite active and inquisitive. They like to explore their environment and may even try to eat the tank’s plants or decorations. This behavior is completely normal and is a sign that your molly fish are healthy and happy.

It’s crucial to remember about molly fish is that they may be rather slightly aggressive to one another at times.

Author’s Note: Trust me, although molly are generally a peaceful fish, they can be somewhat aggressive at times. I had learned this the hard way. I still remember when I got two molly fish beautiful sailfin mollies) for my home fish tank. And one of them just kept chasing the other molly non-stop – to such an extent that I felt it was time to separate them.

It does not imply that they are particularly aggressive. Indeed, I once even had a black-yellow molly fish. That was one of the calmest and friendliest fish I’ve ever had in my fish tank. Basically, it had a voracious appetite. But other than that, the molly didn’t bother any of its tank mates.

Sometimes, male molly fish, in particular, are prone to fighting over territory and females. It may be important to divide your molly fish or give more hiding spots in the aquarium if you see any signs of aggressive behavior.

So overall, although molly fish tend to be very peaceful in groups, sometimes they can be aggressive especially towards each other. So I would recommend keeping them in a tank with enough space to avoid territorial fights.

How Many Molly Fish Should You Keep Together?

Before we talk about the number of molly fish you can keep in a tank, let’s first discuss the size of the fish and the tank space they need.

On average, molly fish grow up to a size of 3 – 4.5 inches long. That means they need enough space to swim and move around.

Each molly fish requires at least 3 gallons of tank space. Therefore, it is essential to have a tank big enough to accommodate the number of molly fish you want to keep.

Gender Ratio:

Molly fish are social creatures and like to swim together. To ensure their happiness and health, you should have at least 3-6 molly fish in a tank. And ideally, that should follow the appropriate male to female ratio. You should have three females for every one male molly fish. This ratio helps to prevent male molly fish from fighting and harassing the females.

Tank Size and the Number of Molly Fish:

Now let’s take a look at how many molly fish you can keep in different-sized tanks. I have created a table below to help you understand the number of molly fish you can keep in a tank.

Tank SizeNumber of Molly Fish
5 Gallons1-2
10 Gallons3-4
15 Gallons4-5
20 Gallons6-7
30 Gallons9-10
40 Gallons12-13
55 Gallons16-18
60 Gallons18-20
75 Gallons23-25

And please remember that if you overcrowd the tank, it can lead to poor water quality and health problems for your molly fish.

Is It Okay To Keep Just One Molly Fish?


Molly fish are a popular freshwater aquarium fish. They are hardy, easy to care for, and come in a variety of colors and patterns.

However, if you’re considering keeping a molly fish as a pet, you might be wondering if it’s okay to keep just one. The short answer is yes, but there are some things you should keep in mind.

First, let’s talk about the living conditions that a molly fish needs. Like all fish, mollies need a tank with a filter, a heater, and regular water changes to keep them healthy.

They also need a balanced diet of fish flakes or pellets, supplemented with occasional treats like frozen or live food. If you can provide these things for your molly fish, then it’s okay to keep just one.

However, keeping just one molly fish might not be the best idea. Mollies are shoaling fish, which means they prefer to be social and remain in groups. 

Now, what should you do if you want to keep a molly fish but can’t get a group of them? The best thing to do is to at least have compatible tank mates from other fish species.

Guppies, neon tetras, platies, swordtails, cory catfish, and other peaceful community fish make good compatible tank mates for mollies.

Just be sure to research the specific requirements of any fish you plan to keep with your molly and make sure they can all live together happily.

Wrapping Up

In a nutshell, a molly fish is not technically a schooling fish, but rather a shoaling fish. Hence, although it is not strictly required, they perform best when maintained as a group.

But it’s also important to consider things like the male to female ratio and having adequate room in the tank for them. A single molly may be housed in a large enough tank if suitable living circumstances are maintained for the fish.

If you currently have a community tank and want to add just one molly to it, that’s OK as well. Just ensure that the tank mates are suitable with the molly.

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