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How Big Do Mollies Get: Size and Care Guide

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By Lindsey Stanton

molly fish

Mollies are some really cool fish that are bright, colorful, and very active. They are great to have in any home aquarium, even larger community aquariums with many different types of fish. However, before you go out and buy any kind of Molly fish, you probably want to know a few things about this species first.

You need to know basic fish info before making a purchase, which is why we are here today. How big do Mollies get? Keep reading to find out.

fish dividerHow Big Do Mollies Get?

One thing that you need to be aware of is that there is more than one answer to this question. This is because there are actually several variations of the Molly fish, all of which have different colorations, sizes, and more.

What we can do is list all of the different kinds of Molly fish and tell you how big each of them gets. This way, you might be able to come closer to a purchasing decision or even purchase more than one kind.

1. Dalmatian Molly

dalmatian molly in aquarium_
Image credit: Eldergeek, Pixabay

This spotted variety of Molly is covered in black and white and can grow to around 4.75 inches in length.


2. Dalmatian Lyretail Molly

This type of Molly fish looks very similar to the normal Dalmatian, except it has a bit of yellow, plus a uniquely-shaped tail. This fish can grow to around 4.75 inches in length.


3. Black Molly

black molly fish
Image credit: Kocsis Sandor, Shutterstock

This Molly fish is simply black. It doesn’t have any other colors, but it definitely looks interesting. The Black Molly can grow to around 3 inches in length.


4. Black Sailfin Molly

This is one of the larger Molly varieties out there. It can grow to around 6.5 inches in length, is black in color, and, as the name implies, has a cool, sail-like fin.


5. Black Lyretail Molly

Lyretail molly in aquarium
Image Credit: Goskova Tatiana, Shutterstock

This is another fairly large type of Molly fish. The Black Lyretail is a mysterious little guy that can grow to around 5 inches in length.


6. Gold Dust Molly

gold dust molly
Image Credit: Praveen Aravind,  Shutterstock

As the name implies, this fish is golden yellow in color, kind of like a goldfish. This guy can grow to around 5 inches in length.


7. Balloon Molly

The Balloon Molly is one of the smaller Molly fish out there. It looks like a little, rounded balloon with yellow and white stripes. It can grow to around 3 inches in length.


8. Marble Lyretail Molly

marble molly
Image Credit: Ramadhan Setia Nugraha, Shutterstock

This peaceful Molly fish has a really nice blue, white, and black marbled pattern. It can grow to around 5 inches in length.


9. Gold Doubloon Molly

gold doubloon molly
Image Credit: Praveen Aravind, Shutterstock

This particular Molly has a really neat color scheme, with the rear being totally black and slowly turning to a bright golden color as you move towards its head. The Gold Doubloon Molly can grow to around 5 inches in length.


10. Harlequin Sailfin Molly

harlequin-molly
Image Credit: bluehand, Shutterstock

Yet another Molly with a neat sail-like fin, plus an awesome marbled color scheme, this fish will grow to around 6 inches in length.


11. Platinum Lyretail Molly

platinum molly
Image Credit:  Mr.Sutun photographer, Shutterstock

This platinum-colored Molly is one of the more interesting looking ones and it can grow to roughly 5 inches in length.


12. Golden Sailfin Molly

This species of Molly looks like a mix between a sailfin Molly and a goldfish. It can grow to roughly 6 inches in length, with the males being substantially larger.

aquarium plant dividerSome Molly Care Tips

If you want your Molly fish to be happy, healthy, and grow to its full potential, there are a couple of tips that you should follow.

Make sure that you have a large tank. Mollies like to have a ton of space. For instance, a Molly that is around 5 inches in length will require a 30-gallon tank. The more space they have, the higher the growth potential.

Make sure to keep the water clean and do regular water changes. You should also make sure to have a good filtration unit. Simply put, it’s harder for fish to grow big and strong when they live in a polluted environment.

Be sure to feed these fish a proper diet. You need to give them a good mix of nutritionally balanced foods to increase their growth potential, increase their bright colors, and keep their bodily functions working properly.

sunburst platy
Image Credit: Joan Carles Juarez, Shutterstock

Commonly Asked Questions

How long does it take for Molly to reach full size?

A full-grown, male Molly fish will usually be around 3 inches or 7 centimeters long, whereas the females are a bit larger and can grow to around 4 inches or 10 centimeters long.

The Molly fish will take around 3 to 4 months to grow to their full size, and, in part, this will depend on their water conditions, diet, and more. With good care, it should take no longer than 4 months for a molly fish to grow to full size.

How fast do black mollies grow?

Black Mollies tend to grow a little bit slower than other Mollies. It may take a Black Molly around 9 to 10 months to grow to its full size, which for males is around 3 inches in length and for females about 5 inches in length, at most.

Molly fish isolated on black background.
Image credit: Oteera, Shutterstock

Do molly fish need to be in groups?

Although this is not 100% necessary, yes, Molly fish should be kept in small groups. While they are not really schooling fish per se, they are used to living in small groups. Molly fish don’t school, but will often develop quite a strict hierarchy among themselves.

If you want to make the most out of your aquarium, you should keep 3 or 4 Molly fish together. These are fairly peaceful fish and they tend to do very well in groups.

How important is tank size for Mollies?

Tank size is quite important for Mollies. Now, they are pretty peaceful fish, and even in small tanks they usually won’t become aggressive towards each other. However, if you want them to grow well, be healthy, and be happy, you do want to provide them with an adequate tank.

What you need to know here is that different types of Molly fish grow to different sizes and, therefore, require different sizes of tanks. For instance, the Short-finned Molly should be fine in a 10-gallon tank but the larger Sailfin Molly will need a tank of 30 gallons.

Normal Mollies are not very large, and you can fit 3 or 4 of them into a 20-gallon tank. So, as you can see, this really depends on the type of Molly and how many of them you have.

What is the biggest molly fish recorded?

The largest type of molly out there is the Sailfin Molly, which usually grows to around 6 inches in length. Some have been recorded to grow up to 8 or even 9 inches in length, although this is very rare.

fish dividerConclusion

The fact of the matter is that there are a dozen or more varieties of Molly fish out there. They are not all the same size, but generally speaking, they will be no shorter than 3 inches and no longer than 7 inches in length.

If you take good care of them and follow the tips we have outlined above, the chances of your Molly reaching its full size is greatly increased.

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Featured image: Praisaeng, Shutterstock

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