How Many Mollies Can You Keep in a 10-Gallon Tank?

When it comes to keeping fish as pets, starting with a small tank is a good idea for beginners. However, one drawback is the limited space for fish. So, how many mollies can comfortably live in a 10-gallon aquarium?

Guidelines for Keeping Mollies in a 10-Gallon Tank

The number of mollies that can thrive in a 10-gallon tank depends on their size. As a general rule, it’s recommended to have approximately 1 inch of fish per gallon of water. With 3-inch mollies, you can keep around 2 or 3 in a 10-gallon tank. If your mollies are smaller, you may be able to accommodate up to 4.

However, it is essential to consider that mollies are active and social fish. They need ample space to swim and thrive. Ideally, they should be housed in a larger tank, such as a 20-gallon one. Additionally, mollies are shoaling fish, meaning they prefer to be in groups of at least six or more in a bigger tank.

Keep in mind that the “one inch per gallon rule” has its controversies. It doesn’t account for decorations, substrate volume, or a fish’s height. This guideline is generally applicable to slender-bodied fish smaller than 3-4 inches in length.

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Male and Female Mollies in a 10-Gallon Tank

For beginners, starting with one male and two females is recommended. This setup allows for a flourishing molly colony over time. Having two females for one male helps distribute attention and reduces chances of bullying. It also ensures that the females have sufficient rest and feeding time, especially during the mating season.

Adding bushy floating plants to the tank provides hiding spots for the females and a resting place for the male molly while he’s not busy chasing his mates. These plants also create safe havens for baby mollies when they are born.

Black Molly Fish in a 10-Gallon Tank

Blackfin mollies typically grow to be around 3-6 inches in length. If you have a 5-inch black molly, you can comfortably keep two in a 10-gallon tank. However, for a 6-inch black molly, it’s best to have only one in a 10-gallon tank. Remember, larger molly fish require more space, and overcrowding can be detrimental.

Sailfin Molly Fish in a 10-Gallon Tank

Sailfin mollies are relatively small fish, usually not exceeding 5 inches in length. Hence, you can keep up to 2 sailfin mollies in a 10-gallon tank without overcrowding the space. These mollies are livebearers, meaning they give birth to live young. To avoid an overabundance of baby mollies, having two female sailfin mollies is a sensible choice. Alternatively, you can opt for a separate breeder tank for the females to breed.

Dalmatian Molly Fish in a 10-Gallon Tank

In captivity, Dalmatian mollies typically reach a maximum length of 4.75 inches. Therefore, you can house around 2 Dalmatian mollies comfortably in a 10-gallon tank. However, keep in mind that Dalmatian mollies are sociable and active fish. It is not advisable to confine them to such a small space for their well-being.

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Lyretail Molly Fish in a 10-Gallon Tank

Female lyretail mollies typically grow up to 5 inches, allowing you to keep two of them in a 10-gallon tank. Males, on the other hand, are shorter, measuring about 3 inches. While it may be tempting to house three male lyretail mollies in a 10-gallon tank, it is not recommended. Males tend to be aggressive towards each other, leading to fights that can be fatal.

Gold Doubloon Molly Fish in a 10-Gallon Tank

Gold doubloon mollies can grow up to 5 inches in length, allowing for two of these fish in a 10-gallon tank. However, due to their high activity levels and swimming needs, it is better to provide them with at least a 25-gallon tank. They require ample space to swim freely and a significant amount of vegetation and hiding spots to minimize stress and prevent disease.

Reasons to Avoid Housing Molly Fish in a 10-Gallon Tank

how many mollies in a 10 gallon tank

They Will Feel Lonely

Mollies are sociable fish that thrive in the company of their own kind. In the wild, they live in shoals of six or more fish. Keeping them alone in a 10-gallon tank can lead to feelings of isolation and distress.

They Will Not Have Enough Swimming Space

Mollies are active swimmers that enjoy moving around. In the wild, they have plenty of space in rivers and streams. However, in a small tank, they will constantly bump into the glass or each other, causing stress and compromising their health.

They Will Not Have Enough Hiding Spots

Hiding spots are essential for mollies to feel safe and secure. In a 10-gallon tank, it is challenging to provide enough decoration or vegetation to create adequate hiding spaces. This lack of hiding spots can make mollies constantly anxious and stressed.

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Their Growth Will Be Stunted

Keeping baby mollies in a 10-gallon tank will eventually lead to their outgrowing the limited space. Once mollies reach their full size, they become too big for the tank, resulting in cramped conditions. Stunted growth can have long-term negative effects on their health and appearance.


Mollies are beautiful and intriguing fish to have in an aquarium, but they require ample space to swim and suitable hiding spots to feel secure. While community tanks with a larger water column can support more mollies, the minimum tank size should accommodate their size and specific needs.

In a 10-gallon tank, it’s possible to keep two mollies if you provide them with proper care and attention. Consider water quality and use appropriate filtration systems based on the specific requirements of your mollies. Remember to test the water regularly for nutrient levels, as they may vary depending on the source.

I hope this article has provided comprehensive information about raising ornamental fish in a 10-gallon tank. If you have any questions, feel free to leave them in the comments below.

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