Molly Fish: Ultimate Care Guide

We explore the care of molly fish, a hardy and adaptable freshwater species native to Mexico and Southern USA. Mollies are peaceful, sociable, and come in various colors, growing up to 4.5 inches in captivity. They thrive in tanks with neutral to slightly alkaline water, at temperatures between 72-78°F. Suitable for beginners, mollies require a minimum 10-gallon tank, clean water, and a balanced diet of invertebrates, plants, algae, and supplemental foods. They are livebearers, easy to breed, and compatible with peaceful tank mates.

The molly fish, otherwise just known as mollies, are a freshwater fish indigenous to Mexico and the Southern USA, are a hardy and easy to care for fish. From the Poeciliidae family, you can find mollies fish in freshwater rivers and estuaries and occasionally making an appearance in seawater. They are quite exotic-looking and will add variety and diversity to your tank. Since the molly fish is easy to care for, they are quite popular in the aquarium trade and they are closely linked to the guppy.

In fact, experts have claimed that guppies and mollies with the breed and mix genes. They are inter-related and from the same genus, which is what makes them compatible. They are an interesting species and will keep your tank bright and lively. They come in a wide variety of shades and it can be tough to narrow down your choices to just one kind. Let’s take a closer look at these active marine creatures.

Information ChartMolly Fish
Care Level: Easy
Temperament: Peaceful
Color: Varied
Lifespan: 5 years
Size: 4.5 inches maximum
Family Poeciliidae
Diet: Omnivorous
Minimum Tank Size: 10 gallons

Care Level

Mollies are very popular due to their hardiness. It’s very easy to care for them, which makes them a great entry point into the aquarium world for beginner aquarists. Due to their popularity, they can be found in almost every fish store and at an affordable price. They are primarily a freshwater fish, but they can be found in seawater at times due to their adaptability.

While they don’t require much are, they do require a clean environment and water conditions. Poor water conditions can lead to “molly disease”, a disease named after mollies because of how common it is. What you will see if your mollies get molly disease is they will become less active and even display odd movements such as wiggling. It’s sort of their way to protest an unideal environment.

If your mollies start to display this behavior, it’s time to check the water quality. It’s not too difficult for these aquarium fish to recover from molly disease. Once the water parameters are back to normal, they will be happy and thriving once again. Molly fish can also suffer from a range of other freshwater fish diseases such as ich. This can be diagnosed upon close inspection of their scales and changes in daily habits.

The best way to make sure your molly fish are properly cared for is to make sure you are keeping the aquarium clean.

Temperament and Behavior

Are mollies aggressive? No, mollies are not generally aggressive and are considered a peaceful species. However, there are certain triggers that can cause aggressive behavior. Among these triggers are a crowded tank or aggressive tank mates. Finding the right tank mates for the molly will provide them with either a soothing or anxious environment (but more on that later).

Other than being a likeable and peaceful species, molly fish are sociable and like to travel in groups. It is recommended that if you keep more than a pair, the shoal of molly fish should be predominantly female as males can be aggressors and create a stressful environment for the females.

What’s very cool about the molly fish is they are small creatures with big personalities. Each one is different too, so it can be a lot of fun to watch them and differentiate between them. Fun Fact: Popular Dog trainer Doggy Dan’s favorite pet than the dog is this Molly Fish.

Black Molly Appearance


Mollies display a diverse range of colors and sizes, influenced by crossbreeding with guppies. Varieties include the solid black molly with distinctive orange tail fins, albinos with pale colors and red eyes, and others in shades of orange, brown, and gold. Males are larger, often with a sailfin, unlike the females. In captivity, mollies reach up to 4.5 inches, slightly smaller than their wild counterparts.

Another unique trait about mollies is that they come in a wide range of colors and sizes. This is thanks to having been bred with guppies over the years. The solid black molly has orange detail on their tail fins and has perky fins all over. The shade of black that they exhibit is very special because there aren’t any other species that come close to the dark black.

There are also albino mollies with pale to white colors and red eyes. You will also be ablet o find orange, brown and even gold mollies. The molly fish is easy to sex. The males are generally larger than the females and have a sailfin, which is absent in the females. Their differences are even more apparent during pregnancy when the females plump up and develop a dark spot on the base of the anal fin.


How big do mollies get? Mollies can get up to 5 inches maximum in the wild. However, they are slightly smaller in captivity as with most other aquarium fish. In your tank, you can expect them to reach 4.5 inches.


Let’s take a closer look at what different types of mollies look like.

Black Molly Fish

The common molly and the black molly fish are essentially the same. You can tell that you have a black molly fish due to the solid black coloring.

Lyretail Molly Fish

When they have the word “tail” in their name, you would expect to recognize them through this trait. The lyretail molly how long and flowy caudal fin, dorsal fin and anal fin that taper off into points.

Sailfin Molly Fish

The sailfin molly has special fins. The dorsal fin resembles a sail and is much larger and taller than other molly fish.

Balloon Molly Fish

The balloon molly fish is a plump little creature with a rounded belly and comes in black, yellow and white.

Dalmatian Molly Fish

The dalmatian molly is exactly as you would picture. They are white/silver-based with black speckles all over their body.

Red Molly Fish

The red mollies have dark orange or red bodies with black fins.

Orange Molly Fish

Orange mollies have a lighter hue compared to red mollies and can sometimes have silver underbellies.

White Molly Fish

The white mollies are beautiful and have a milky white or silvery shade without any other color.


How long does a molly fish live for? The molly can live up to 5 years in captivity. The best and safest way to make sure your mollies live a long and healthy life is to maintain the aquarium in the best way and monitoring water conditions consistently.


It’s slightly more difficult to feed omnivorous fish just because there is a lot more you need to balance. This species mostly feed off of invertebrates, along with plants and algae in the wild. This makes keeping their diet in the aquarium easy since it’s not that difficult to mimic this diet in captivity.

Since they eat algae, they can be considered tank cleaners. This means they will help you maintain the conditions of the tank and require less cleaning on your part. Supplement their need for veggies with ingredients you can find around your kitchen. A good place to start is with blanched vegetables such as lettuce and spinach. They can also feed off of fish flakes and pellets but it’s always a good idea to supplement this diet.

For the protein aspect of their meals, look into keeping blood works and brine shrimp handy. Frozen foods are easy and convenient for your mollies but feeding them live food can make mealtimes more interesting and hone their natural scavenging skills.

As for how much you should feed your mollies, try to aim for small amounts since they are tiny creatures. Clear whatever they cannot finish within a 2 min period and consider that the right amount. They don’t need to eat too often, twice a day will be enough.


The mollies are from the poeciliidae family and are freshwater marine creatures native to Southern USA and Mexico.

Tank Conditions

Fortunately for beginners, mollies don’t need a specific setup in the tank. This is thanks to their being bred for years in captivity and they have become well-adapted. If kept in a tank with other fish, you can first consider the needs of other species before the mollies. Sandy substrate is recommended just so you can keep vegetation in your tank.

To keep them happy, give these little fish with big personalities with things to do like tall plants to hide between. Satisfy their natural curiosity with artificial caves and rocks to explore. Since they are a tropical fish and are used to warmer waters, there is a chance you will need to purchase a water heater to maintain the temperature.


The recommended temperature for mollies is between 72-78 degrees Fahrenheit (22-25.5 degrees Fahrenheit). Since this is the natural temperature of freshwater estuaries which they are native to, they will adapt to aquarium life better with these water conditions.

Water Conditions

As for the water quality, keep the pH relatively neutral or slightly alkaline at pH 7.5-8.5 with a 15-30 dGH water hardness.

Minimum Tank Size

We would suggest a 10 gallon tank for starters for 1-3 mollies but larger species will need larger tanks to start with. When you exceed 3, you should double the tank size.

Maintenance and Care

Mollies are very adaptable and hardy little fish. What you should do to regularly maintain the aquarium environment is to always clear out the leftover food. Other than that, changing out the water and the specifics of the water quality can be altered to fit more delicate fish in your aquarium.

Changing the water out as necessary for other species is also a good idea. The mollies can adapt well, as long as the water conditions are within their acceptance. They can even live for shorter periods in saltwater if necessary.

If by any chance you suspect your mollies of developing common diseases, it’s a good decision to isolate the suffering mollies in a new tank to give them space to heal without contaminating the rest of the tank.

Suitable Tank Mates

Peaceful fish are the easiest to find tank mates for. Since the mollies are such a likeable species, they can geta long with other peaceful species (of similar size) in a community tank. Although you need to make sure aquariums are large enough for all species since crowded spaces is an imperative factor, which can set off a molly’s aggression.

Definitely avoid aggressive fish regardless of the size. Since mollies are cleaner fish, they can get along well with other invertebrates that share the same role. Shrimps and snails can be added to your community aquariums to help maintain tank conditions.


What kind of fish can live with mollies? They can live with almost any peaceful fish. These include barbs, catfish, danios, tetras and loaches. Other mollies are a great choice as well, just make sure that the shoal is predominantly female as the males can stress their counterparts out. If you do intend on keeping them together, you should make sure your aquarium has at least 4 mollies.


Breeding mollies is straightforward in captivity. They are livebearers, with females gestating eggs internally before release. Gestation lasts 35-45 days, and large females can produce up to 100 fry per mating. It’s crucial to separate fry from parents to prevent cannibalism.

How do mollie fish mate? Studies have been conducted on mating preferences of the molly fish depending on the environment. What’s cool about the mollies that isn’t commonly seen in other fish is how they gestate their fry. Mollies are what we call livebearers, which means they don’t lay eggs. What the females do is they allow their eggs to develop inside them before being released.

If you are planning to breed your mollies, you will be happy to know that they are easy to breed in captivity and they will do so regularly. One thing that you do need to pay attention to is the aquarium conditions. You need to keep everything perfect to trigger mating. Your mollies need clean aquariums to breed with slightly warmer water. Depending on the usual temperature you keep it at, we suggest raising it just a couple of degrees or so but do not exceed the temperature range.

You will know you have been successful in triggering mating when you see the males start to court the females. The females call the shots and will only allow the males to fertilize the eggs when she is ready. The males can get quite impatient and will try to “sneak attack” but it’s often unsuccessful and the females will retaliate. You can also assume which male (if there are more than one) the female will choose to mate with. The female mollies will often choose the largest male molly in the aquarium.

Once successful, you will see the female’s belly begin to swell. It will be very apparent when compared to other mollies in the same aquarium. Since this species is a livebearer, it will take longer for you to see the fry. Gestation takes about 35-45 days after fertilization and only then will you see the young and be sure of success. Every female can carry fry and the larger ones can produce up to 100 in one mating.

The fry look like the parents straight out of their mom, but may have heard of some species eating their eggs, and the molly is no different. it may even be said that they are worse since they may eat their young that have already developed past the egg stage. Due to this, it’s best to separate the fry from their parents. For breeding, it’s wise to have two aquariums, one for breeding purposes and the community tank.

Regardless of how you separate the young and the parents (through separate aquariums or a breeder box), you need to remove the fry from the parents. You can also do the separating before the fry are released by removing the female before birth. This is also a good idea since they require different food. For the fry, feed them small pieces of fish flakes until they are large enough to eat the same food as their parents. When they are, you can reintroduce them into the same aquarium.


Mollies are easy to care for in every sense. Keeping them with other fish is easy, and they are known to be very interesting with colorful personalities. This is why there is no reason not to get mollies, especially if you want diverse aquariums with little splashes of color. They are even an easy species to add to your existing aquarium. You just need to make sure the aquarium parameters are ideal and feed them the right amount of food.

Balanced meals and nutrition are also crucial elements to the longevity of your aquarium fish. When introducing a new school, make sure you keep up to 4 mollies in the same aquarium. They do like to school together but keep in mind that they need enough space. It’s okay if you are a beginner and not fully experienced in maintaining the condition of the aquarium. Mollies are very adaptable and a hardy species that can tolerate changes.

Just be sure to keep the water conditions within the permissible range. The personalities of your new mollies will present themselves over time. If you have the same species of mollies, you may even be able to name and recognize them based on their personalities upon careful observation.

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