Molly fish are a staple of freshwater fishkeeping, and have been popular among aquarists for quite a while! These fish are known for their low-maintenance care requirements and wide selection of possible species to choose from.

But even though caring for them is straightforward, we always encourage owners to develop a strong knowledge base about this species. This will help you keep them happy, healthy, and save you time in the long run.

This guide on molly fish care has everything you need to get started. You’ll learn about their tank setup, food, lifespan, and even breeding tips! Oh yeah, we also list the most common types of mollies for you to consider as well.

Species Summary

There’s no doubt that you’ve seen a molly fish (Poecilia sphenops) at some point. Mollies are one of the most popular freshwater species in the aquarium trade. Often sold for a few bucks each, they’re the perfect species for beginners.

However, many seasoned aquarists enjoy them too!

A group of mollies swimming in a freshwater tank

Peaceful by nature, the molly is great for freshwater community tanks. They’re easy to care for and can adapt well to most standard tank setups.

In the wild, you can find mollies throughout North and South America. They typically inhabit slow-moving tropical rivers teeming with vegetation.

Since their introduction to the world of fishkeeping, mollies have been cross-bred a lot! As a result, you can find a wide range of colors and species to enjoy.

Appearance

When most people think of molly fish, they picture the common molly. While there are several varieties out there, most have a similar shape and body style to the common molly.

These fish have a flattened body with a triangular-shaped head. Wide at the mid-section, the body tapers down to a narrow point at the snout. On the other end, the body tapers slightly towards the base of the fan-shaped tail.

Male and female molly fish are pretty easy to differentiate. Males are usually smaller and have a pointy anal fin. The anal fin of the female is broad and fanned. Many females also have a visible “gravid” spot, which is where they hold their young during pregnancy.

Author Note: You’ll encounter a spectrum of interesting-looking mollies in the aquarium trade. These fish are part of the Poecilia genus. With the exception of the Endler’s livebearer and the guppy, every fish in this genus is a molly!

Common Types Of Mollies

There are reportedly around 39 different species. Below are just a few of the more popular ones. If you’re looking for something a bit less popular, you’ll probably have to do a little digging (since they might not be at your local fish store).

Black Mollies

Black molly fish swimming with other mollies

As you can guess, these mollies are covered in black! You might see some splashes of yellow or orange on the fins, but most of the body is pure black.

Sailfin Mollies

The sailfin molly has the standard body shape. However, the dorsal fin is much taller and stretches to the base of the tailfin. You can find sailfin varieties in many colors (including black).

Balloon Mollies

A light colored balloon molly fish

Balloon mollies are appropriately named for their bellies. Even when not pregnant, the belly takes on a round and bulbous shape. Like the sailfin, different colors of balloon mollies are available.

Lyretail Mollies

The lyretail molly has a beautiful tailfin. It features the same fanned shape as other mollies. However, the top and bottom have lengthy rays to create a forked appearance.

Dalmation Mollies

A Dalmatian molly fish in a freshwater aquarium

Very popular in fish stores, the Dalmation molly is covered with a base color of white. Specks of black adorn the body, making it look like a Dalmation dog. Dalmation mollies can be standard, lyretail, balloon, or sailfin!

Gold Doubloon Molly

The gold doubloon molly is another frequently purchased species. The front half of its body is a vibrant yellow, and the lower half is pure black.

Molly Fish Lifespan

The average molly fish lifespan is around three to five years. While they aren’t the longest-living freshwater species out there, there is some wiggle room depending on what species you get.

The quality of care you provide will also impact their lifespan significantly. While hardy, mollies are prone to disease from a poorly maintained environment just the same.

Author Note: Some species of mollies are more susceptible to bad water conditions than others, leading to a much shorter lifespan. While your goal should be to always provide the best care possible, it’s recommended to understand details about the specific species you own.

Average Size

Four to four and a half inches is the normal size range of a full-grown molly. This length is rather manageable, and allows them to be kept in reasonably small aquariums.

Sailfin varieties can get even bigger. They will often reach lengths that are closer to five or six inches.

Molly Fish Care

Molly fish care is something that pretty much anyone can do. They don’t require a lot of work to keep healthy, making them a great choice for anyone interested in getting started with fishkeeping.

As long as you follow the following established care guidelines, your mollies should thrive!

Tank Size

Thanks to their small size, mollies do just fine in small and medium-sized aquariums. Most molly fish can live happily in a tank size as small as 10 gallons.

That tank size recommendation is suitable enough for up to four mollies, although a larger tank is always appreciated if you have some extra space. For a larger group, you need to bump up the tank size by at least three gallons of volume per fish.

Author Note: The only exception for tank size revolves around the sailfin molly. These fish get slightly bigger than your average molly, meaning they will need a bigger tank to prevent stress.

For sailfin varieties, aim for a tank size of 30 gallons or bigger.

Water Parameters

The habitat of mollies in the wild can vary quite a bit. These freshwater fish have a wide natural distribution. While most are found in rivers, they can also swim into brackish waters or even the open ocean for short periods!

As a whole, mollies are very adaptable. They like warm waters, neutral pH, and hard water. Contrary to the belief of some, you don’t need salt in the water to keep these fish healthy. They do just fine living in pure freshwater environments their entire lives.

Exact water parameters may vary based on the species you get, but here are some good baselines that will work for most mollies.

  • Water temperature: 72°F to 78°F (some species as high as 80 degrees)
  • pH levels: 7.5 to 8.5
  • Water hardness: 20 to 30 KH

We recommend that all aquarists go out and get a reliable (and accurate) water test kit. This will be your lifeline when it comes to understanding the state of your tank at a glance, and making adjustments when necessary.

What To Put In Their Tank

Mollies do very well with natural decor that mimics the tropical rivers they inhabit in the wild. This means adding plenty of plants and lots of places to seek shelter.

At the bottom of your tank, add sand or gravel substrate. Mollies spend most of their time in the middle and upper parts of the water column. They won’t spend too much time down near the substrate.

Author Note: Generally, sand substrates are best if you want plants. The molly can also benefit from aragonite sand, as it disperses beneficial minerals into the water.

Using the substrate as an anchor, add several live plants (mollies use these plants for shelter). It’s good to provide taller plants like Anubias as well as shorter varieties like Java fern. When you arrange the plants, position them along the perimeter of the aquarium so that there’s still open swimming space.

Finally, round off the decor with some rocks, caves, and driftwood. Those items will provide some additional shelter. Plus, they can develop algae for your mollies to snack on.

Lighting & Filtration

Standard lighting is fine. Mollies aren’t picky about lighting levels, but you do need lights to keep the plants healthy.

One thing you will need is a strong filtration system since mollies are big waste producers. A small group can easily raise ammonia and nitrate levels to unhealthy levels. Choose a powerful filter that can hold a lot of biomedia. Additional internal or external sponge filters are great, too.

Common Possible Diseases

Like any other fish, mollies can suffer from disease. There are a couple of unique ailments you have to watch out for. These include molly disease and constipation.

Molly disease, also known as the “shimmies” is something to be aware of. It occurs when the water parameters are not stable. Many aquarists notice the disease with extreme temperature changes or ammonia spikes.

A molly fish swimming alone

With the disease, the molly fish is unable to swim properly. Instead, they “shimmy” and wiggle in one place. The good news is that most fish heal up quickly once conditions are fixed.

Constipation is a problem that affects balloon mollies. The body shape of this fish results in compacted organs. Eating too much or too fast could result in potentially dangerous constipation, so you must stay on top of their eating habits.

Beyond those two issues, mollies can also suffer from common freshwater diseases. They can experience Ich, bacterial infections, flukes, and parasites.

Author Note: The best way to avoid disease is to monitor water conditions. It’s also important to change 25 to 35 percent of the water weekly to ensure that ammonia and nitrate levels don’t rise.

Molly Fish Food & Diet

Molly fish mostly consume plant-based foods. While they’re not considered a great algae-eater, they do like to snack on it frequently. You can find them using their lips to scrape it off rocks, wood, and glass.

Beyond algae, these fish enjoy blanched vegetables like lettuce, spinach, and zucchini.

The occasional high-protein snack is appreciated, too. Mollies will accept live or frozen bloodworms, daphnia, and brine shrimp. In addition to their nutritional benefits, live foods provide some much-needed stimulation during feeding time. It’s a good idea to try and implement it into your fish’s diet every once in a while.

For simplicity, dry commercial flakes and pellets are a good food source to consider as well. Look for nutritionally balanced products from well-respected brands!

Behavior & Temperament

Overall, mollies are easy-going fish. They’re peaceful and do well with others.

Mollies are a shoaling fish, so they need to be in the presence of others to feel comfortable. You should keep a group of at least four fish at the very least. An even larger group is better if possible!

These fish will group up to explore the tank and swim around as one unit. Then, they’ll go off and do their own thing.

Author Note: The only time you might see aggression is if you keep males. Males can harass females, but this behavior only gets worse if the conditions are right for breeding.

While this behavior isn’t particularly violent, it can cause stress in females. Make sure the females outnumber the males to keep this behavior to a minimum.

Tank Mates

You have a lot of options if you’re looking to create a multi-species community tank. Mollies get along with just about anything!

As long as the other tank mates are peaceful, mollies won’t have any problems living with them.

Avoid any fish that’s known to exhibit aggressive behavior. Also, try to keep similarly-sized fish. Larger fish could bully or even try to eat your molly.

Here are some solid tank mates choices for the molly fish:

Molly fish will also get along with most freshwater aquarium shrimp and snails quite well too. You really have plenty of options!

Breeding

The molly fish breeding process is extremely interesting and fun for those who are interested. Not only that, but they breed a lot! Healthy mollies can spawn new fry several times throughout their lives. Oftentimes, it occurs with no intervention from humans.

These fish are livebearers. Rather than laying eggs, the female will hold them in her belly until the babies are ready to hatch. Then, she releases fully formed and free-swimming fry into the water!

If you want to maximize the survival rate of the fry, it’s best to breed mollies in a controlled environment. Create a separate breeding tank with slightly warmer temperatures up to 78 degrees Fahrenheit.

Females are more likely to breed with the largest male. Place the pair in the breeding tank and watch the mating ritual! The males will court the females before she allows them to fertilize the eggs.

Before long, your female will start to balloon in size when pregnant. It takes about 35 to 45 days for the babies to grow inside her. When she’s about to give birth, place her in a breeding box.

Mollies don’t display any parental instincts, and most will attempt to eat the babies. Breeding boxes keep the female contained while the fry slips down through the bottom.

Healthy adult mollies can give birth to as many as 100 babies at one time! You can feed the fry infusoria or powdered fish food. Once they get a bit bigger, move onto baby brine shrimp until they can consume standard foods.

Conclusion

Molly fish care is really a piece of cake. These are one of the most beginner-friendly freshwater fish out there.

There’s a reason why they’re so popular!

Low-maintenance fish that look great and put on a show are a great choice for anyone. Enjoyable and stress-free fishkeeping is as good as it gets.

Over time we’ll be adding more species-specific care guides to our site. So if you’re looking for information on specific types of molly fish, check back soon!

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