How Many Mollies Should Be Kept Together?

Mollies are among the most popular freshwater fish that fish enthusiasts keep. They’re native to Mexico and the Southern US.

As attractive fish that are easy to care for, mollies are a perfect choice for beginners.

Since they’re available in a variety of shapes and colors, you have many options to choose from when it comes to selecting mollies.

In this article, you’ll learn a lot about this interesting fish, including how many mollies should be kept together in a tank.

How Many Mollies Should be Kept Together in a Tank?

As you spend time with mollies, you will be impressed by their unique personalities and interesting behaviors.

Hence, you’ll want to add more mollies to your aquarium soon. But how many mollies can you add to a fish tank?

To get the answer, it’s important to understand how mollies typically behave.

Even though they are mostly peace-loving and social, mollies can get aggressive when there are too many fish in the aquarium or they are surrounded by other aggressive fish.

That’s why you should pay particular attention to the size of your aquarium and the choice of tank mates when keeping mollies.

Ideally, you should have a 10-gallon aquarium for a molly fish.

Depending on the species, you may add up to four mollies to the tank. For Sailfins and other larger mollies, however, you’ll need to arrange a 30-gallon aquarium. To live comfortably, each extra molly will require about 3 additional gallons.

Mollies tend to stick together most of the time, which is why you should keep them in groups of 4 or more.

If you are planning to keep more than 4 mollies, make sure you get a 20-gallon tank at least.

A 45- gallon tank should be a perfect choice if you plan to manage multiple shoals of mollies.

Keep in mind that male mollies are known to harass and stress females. To prevent aggressive behavior, a shoal should thus be dominated by females.

Hence, it’s extremely important to consider the two sexes when setting up your fish tank. We recommend a ratio of three females to one male.

Since male mollies are aggressive breeders, adding more females should divert the males’ attention between them.

This way, no one female will get constant attention.

Not following this ratio will stress out female mollies; hence, they’ll stop eating and eventually starve to death.

Best Tank Mates to Add With Mollies

Don’t forget to consider what tank mates you can add with mollies.

As stated earlier, mollies are peaceful fish that get along well with other peace-loving community fish.

A few fish tank mates that will live in harmony with mollies include other mollies, Guppies, Tetras, Swordtails, Platies, Danios, Gouramis, and female betta fish.

Types of Mollies

There are numerous types of mollies out there.

While most resemble the common molly, known as Poeciliasphenops, others greatly differ in colors, patterns, shapes, and sizes.

Before studying the different types, it’s important to understand the features of the common molly.

The wild, short-finned molly features a dull silver color, with scattered black dots on the skin.

At the end of its rounded caudal and dorsal fins lies a bright yellow fringe.

These species exist in many colors, but the most commonly found varieties include black, silver, and yellow-orange.

The common molly has an oblong body, with a small dorso-ventrally flattened head and round caudal peduncle.

Its protruding jaws serve as a scraping tool designed to rasp algae off benthic surfaces.

Its mouth contains multiple rows of minute teeth, with the innermost row being the smallest. The size tends to increase with each successive row.

The common molly demonstrates sexual dimorphism.

This is a condition where the two genders of the same species possess different characteristics other than their sexual organs.

The condition is displayed in common molly in that the male species are smaller and more colorful than their female counterparts.

Males also feature a modified fin, which is referred to as gonopodium, to transmit sperm while mating.

Now, let’s explore the most popular types of molly fish:

Lyretail Molly Fish

Lyretail Molly Fish

Lyretail molly stands out from the rest due to its long, flowy caudal fin, anal fin, and dorsal fin, which narrows into points that trail behind the fish.

Sailfin Molly Fish

Sailfin Molly Fish

Sailfin fish are known for their special fins.

As their name suggests, their dorsal fin looks very similar to a sail and is taller and larger than those of other mollies.

Its dorsal fin runs from behind its head to just before its caudal fin.

Sailfin mollies are bred in a variety of different patterns and colors.

Balloon Molly Fish

Balloon Molly Fish

Balloon mollies are plump little creatures that come in black, white, and yellow colors. They earned their name for their round bellies.

They prefer living in hard water with a slightly high pH (7-8).

Also, note that these are man-made fish species (created with the hybridization of the sailfin molly). So you won’t find it in the wild.

Black Molly Fish

Black Molly Fish

These are totally black in color and are no different than the common molly discussed above.

White Molly Fish

These beautiful mollies have a silvery or milky white shade.

Dalmatian Molly Fish

Dalmatian Molly Fish

The dalmatian breed not only exists in dogs but also in mollies.

Just as you’d picture them, dalmatian mollies possess white/silver bodies with black speckles all over them.

Orange Molly Fish

These are light orange in color with some species containing silver underbellies.

Red Molly Fish

The red mollies have a darker hue as compared to orange mollies and feature black fins.

Tank Setup and Conditions for Mollies

Having been bred in captivity for a while now, mollies have become well-adapted to varying tank setups.

This, again, makes them ideal for beginners. When you want to keep mollies together with other fish, you should be more concerned about the needs of other fish.

To maintain decent vegetation in your aquarium, a sandy substrate is recommended.

Incorporate rocks and artificial caves that they can explore to satisfy their natural curiosity. Providing them with tall plants to hide should also keep them happy.

As tropical fish, mollies are more comfortable with warmer waters. Therefore, maintain the water temperature using a water heater.

Let’s discuss each tank condition separately:

Water Conditions

Mollies live well in brackish water (as they are used to it when living in the wild).

You can keep these in your home aquarium in hard water with some added salt (while making sure that other fishes can also survive in that type of water.

Maintain a slightly alkaline pH or a relatively neutral pH of around 7.5-8.5. Water hardness should be between 15 and 30 dGH.


Mollies thrive best in temperatures ranging between 72- 78 degrees Fahrenheit.

This is the natural temperature of their native freshwater estuaries. Hence, they’ll likely adapt well to the same water temperature range in aquariums.


Mollies mostly feed on invertebrates, plants, algae, and live food (brine shrimp, daphnia, or mosquito larvae).

Since it isn’t hard to mimic this diet in captivity, providing them food should be easy. Since they like to eat algae, they can assist in keeping your tank clean.

Since much of the algae will be consumed by mollies, you’ll need to put in less effort for maintenance.

Use different ingredients you see in your kitchen to supplement their need for veggies.

Blanched vegetables, such as spinach and lettuce, are good options. If you want to provide fish pellets and flakes, consider supplementing this diet too.

For the protein aspect of their food, you may choose frozen foods.

However, if you really want to hone their natural scavenging skills, make their mealtimes more interesting with live food (such as (brine shrimp, daphnia, or mosquito larvae).

As for the quantity of food, consider giving small amounts as mollies are small creatures.

They only need to be fed twice a day and if they don’t finish something in a period of 2 minutes, clear the remains.

Also read: Why Does Molly Fish Eat at the Edge of the Aquarium?

Tank Maintenance

When keeping mollies, the most important aspect of tank maintenance is clearing out the leftover food.

If there are other more delicate fish in the aquarium, you’ll need to change the water and alter the water quality.

As for mollies, they’ll adapt fine as long as the water conditions are within their acceptable range (they prefer slightly hard brackish water).

If necessary, you may keep them in saltwater too but for a short period.

If any of the mollies develop a disease, isolate them in a separate tank until they heal so that they don’t contaminate the rest of the aquarium.

How to Breed Mollies?

Mollies are among the easiest fish to breed in captivity and will normally mate on a regular basis.

They are livebearers, meaning their eggs grow within their bodies and the fish releases live fry.

Also read: How to Protect Fish Eggs in an Aquarium?

To encourage breeding, the water should be clean and other conditions need to be perfect.

To trigger mating, slightly raise the temperature but don’t increase it higher than 78 degrees Fahrenheit.

Females allow males to fertilize their eggs when they’re ready to mate, while males perform a courting display for females.

Females prefer to mate with the largest males.

Females take 35 to 45 days after fertilization to release the fry and larger females can release as many as 100 juveniles.

Adult mollies, regardless of gender, have a reputation to eat their offspring.

So, it’s important to separate the fry from them. One strategy is to keep pregnant mollies in a breeder’s box before they give birth.

The box contains holes so the young can leave the box and adults stay trapped in it.

Closing Thoughts

To sum everything up, mollies are ideal creatures for aquarium enthusiasts, especially those who’re just starting out.

If you are getting a molly just remember to keep them in groups of 4 in a 10-gallon tank.

Now that you’ve gained a lot of insight into mollies, including how many you can keep together in an aquarium, go ahead and get them for your tank!

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