Molly Fish

Molly Fish: The Ultimate Guide to Care and Maintenance

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Molly fish are amazing species and come in a wide variety of colors and fin shapes.

Stalwart and active, if provided with the right conditions, they can live up to 3-4 years and produce thousands of fries during their lifetime.

Known for their low-maintenance care, these fish can be a wonderful addition to your fish tank.

In this article, we will show you everything to start keeping molly fish. You’ll learn about their nature, food, tank setup, lifespan, and even breeding tips. Here we’ll help you build a healthy and happy molly fish tank.

Now let’s dive deep into the details.

Molly Fish – Natural Habitat & Identification

Molly Fish - Narural Habitat & Identification
Molly Fish – Natural Habitat & Identification

The natural environment of molly fish can vary greatly. They are excellently adaptable and can live in freshwater, brackish water, and even saltwater.

The only problem they have with water is soft water – which is crucial to note for some other types of fish you house them with. Interestingly, these fish can be tolerant of high hydrogen sulfide levels.

Most of the time, molly fish come from shallow rivers, streams, and swamps in Central, North, and South America. They often swim through the shallows along the edges of these places, and lowland streams, estuaries, ponds, and marshes.

The natural substrate in these locations is sandy with debris and rocks on the top. That gives you a clue as to what kind of tank we should raise them in.

In the wild, mollies are surrounded by lots of aquatic plants. The plants offer shelter and food for them, particularly during the reproductive period. The rivers in which they live are semi-tropical or tropical, so the plants get a considerable supply of sunlight to grow.

Moreover, floating vegetation also gives the fish a protective shield, so they can hide their predators.

The water where these fish inhabit is naturally slow-moving and warm, with a pH that is towards slight alkalinity.

With a flattened body, molly fish feature a “tall” center narrowing into a point at the mouth. They have big caudal fins that are fan-shaped and are either colorful or transparent. The dorsal fin has a similar shape or flattens against the body, depending on each species.

Care Level of Molly Fish

Molly fish have become popular, thanks to their hardiness. They are freshwater fish but can still be found in seawater at times, thanks to their incredible adaptability. It’s super simple to care for them, which makes them a wonderful entry point into the aquarium world for novice aquarists. You can find this species at almost every fish store at a reasonable price.

Though the fish don’t require much care, they do need a clean habitat and proper water conditions. Poor water conditions can cause “molly disease”. If your fish get “molly disease”, they will become less active and have odd movements such as wiggling. It’s their way to oppose an unideal habitat.

If your mollies begin to have this behavior, it’s about time to check the water quality. It’s not too hard for them to recover. As soon as the water parameters are adjusted to normal, the fish will be happy again.

Moreover, molly fish might suffer from a number of other freshwater fish diseases, like ich. Keepers can notice this via close inspection of their scales and some changes in everyday habits.

Temperament and Behavior

Molly fish are considered peaceful species. However, there are some triggers that can lead to aggressive behavior. For example, they live in a crowded environment or have aggressive tank mates.

Molly fish are social and prefer staying in groups. If you raise more than a pair, there should be more females than males. This is because males tend to be more aggressive, creating a stressful environment for females.

Common Types of Molly Fish

Types of Molly Fish
Types of Molly Fish

Sailfin Mollies: The sailfin molly features a standard body shape. However, the dorsal fin is far taller and runs to the base of the tailfin.

Balloon Mollies: This type is named for their bellies. Even when not pregnant, the belly has a round and bulbous shape.

Black Mollies: These mollies are covered in black. There might be some splashes of orange or yellow on the fins, but most of the body is black.

Dalmation Mollies: These fish is covered with a base color of white. There are specks of black along the body, making it similar to a Dalmation dog.

Lyretail Mollies: These mollies feature a stunning tailfin. It has the same fanned shape as other mollies. However, the bottom and top have long rays to generate a forked appearance.

Gold Doubloon Mollies: The front half of the body is a bright yellow, while the lower half is covered with pure black.

Set Up a Molly Fish Tank

Molly Fish Tank
Molly Fish Tank

Tank Size

Molly fish can live comfortably in small and medium-sized tanks, thanks to their small size. Most of them do just fine in an aquarium as small as 10 gallons in capacity.

That aquarium size is proper enough for 1 to 3 mollies. However, a larger aquarium is always appreciated if you have some additional space. For a bigger group, you have to increase the tank size by at least 3 gallons tank of volume per fish.

Notice: If you decide to raise sailfin mollies, they require a larger tank to prevent stress, at least a tank of 30 gallons.

Water Parameters

The environment of mollies in the wild is various. These freshwater species have a huge natural distribution. While most live in rivers, they also move to brackish waters or even the open ocean for short periods.

Generally, mollies are greatly adaptable. They prefer warm water, neutral pH, and hard water.

Precise water parameters might be different, depending on the species you keep. However, here are some baselines that work for most fish.

  • Water temperature: 72 to 78 degrees Fahrenheit
  • pH levels: 7.5 to 8.5
  • Ammonia/Nitrite: 0 ppm
  • Nitrate: <30 ppm
  • GH: 12-25 dGH (200-416 ppm)
  • KH: 10-25 dkh (178-450 ppm)


Molly fish are tropical species that require 75 to 80 degrees Fahrenheit temperatures.

A heater is of absolute importance, which keeps the water warm and maintains it at a stable temperature.


Mollies might be love, but also very messy. They usually gobble food as if they’re starving, so they produce a lot of waste.

All that waste will sink to the bottom of your aquarium. Then it begins to break down, releasing ammonia (NH3). This is bad because even a small amount of ammonia is harmful to fish and inverts.

Luckily, there are bacteria in our filters. One kind absorbs ammonia and turns it into nitrite, another harmful byproduct. However, then another species of bacteria will consume the nitrite and release something called nitrate.

This entire process is called the aquarium nitrogen cycle.

Hence, you need to use a filter that can capture enough beneficial bacteria to catch up with processing tons of waste from mollies. Choose a filter that can keep a lot of bio-media and you can add another filter, such as an internal or sponge filter.


Molly fish prefer an aragonite sand substrate. Aragonite is made of calcium carbonate that will slowly give off minerals that the fish will love.

If using a gravel substrate, you can consider adding a few cups of crushed coral to the gravel. It will work the same as aragonite.


Aquarium lighting is vital for the proper growth of molly fish. Lighting helps to simulate your fish’s natural habitat in your tank and regulate your fish’s eating and sleeping. 

Plants need light for photosynthesis. For a tank with only your mollies, you just add the amount of light to see your fish. As low light won’t promote algae bloom in your tank, you can light your aquarium for a few hours. 

However, if you keep plants in your tank, one to five-watt per gallon of water will work. You have to light your fish tank for 8-10 hours per day on average. 

Read more: Best LED Aquarium Lights

Plant and Decoration

Molly fish are active, top-dwelling species. Therefore, they require lots of open swimming areas.

Meanwhile, they also love densely planted tanks and maybe some decorations and rocks that provide some hiding spots.


Molly fish are highly adaptable and hardy little creatures. What you need to do to maintain the tank habitat is to always get rid of leftover food. Additionally, changing the tank water and the specifics of the water quality can be adjusted to fit more delicate fish.

It’s always important to change the water. Mollies can adapt well, provided that the water conditions are within their acceptance. They can even survive for short periods in a saltwater environment if needed.

Whenever you suspect your fish of experiencing common diseases, let’s isolate the sick mollies in a different tank, giving them space to heal without contaminating the rest of the aquarium.

Tank Mates

It’s essential to note that molly fish are very social shoaling species. They prefer being kept in groups.

It’s ideal for raising one male with every three females. Males often harass females, attempting to mate with them. Having several fish means no fish is stressed by the male’s attention.

Mollies are a peaceful tank mate. Besides, they’re greedy feeders that might outcompete small fish for food.

Here are some types of fish you can add to your molly tank:

  • Swordtails
  • Clown and Bristlenose Plecos
  • Platies
  • Corydoras catfish

Read more: 18 Most Friendly Betta Fish Tank Mates


As omnivores, molly fish can feed on a variety of food types. In wild habitats, they eat small invertebrates, but mainly algae and plants.

Algae is a staple part of their diet. Mollies use their lips to scrape it from the water surface, which makes them great tank cleaners. You can supplement their need for vegetables with ingredients in your kitchen. For example, you can use blanched vegetables like spinach and lettuce. Moreover, you can feed them fish flakes and pellets as well.

For the protein part of their meals, bloodworms and brine shrimp are excellent sources. Frozen foods are also convenient for your fish, but giving them live food can make meals more interesting and improve their natural scavenging skills.

When feeding your molly fish, try to feed small amounts at a time.


Molly Fish - Breeding
Molly Fish – Breeding

Fertilization and Gestation Period 

Research has been done on the mating preferences of molly fish based on the environment. What’s interesting about the fish is how they gestate their babies. Mollies are livebearers, which don’t lay eggs. What the females do is they let their eggs grow inside them before being released.

If you tend to breed your mollies, you’ll be pleased to know that they are simple to breed in captivity. One thing to pay attention to is the tank conditions. You have to keep everything proper to trigger mating. Your mollies require clean tanks to breed with slightly warm water.

When the males begin to court the females, you have succeeded in triggering mating. The female calls the shots and only lets the male fertilize eggs when she’s ready. The male might become impatient and try to “sneak attack”. However, it’s often unsuccessful and the female will retaliate. If you have more than males in the tank, the female will pick the biggest male molly to mate with.

Once the mating is done, the female’s belly starts to swell. Gestation will take from 35 to 45 days after fertilization. At this time, you will see changes in the female body. Interestingly, in fact, females can store sperms for several months. They can get pregnant even if there are no male mollies in the aquarium. 

Molly Fish Babies

In the following stage, females give birth to lovely little babies after the gestation period. Unfortunately, the mother can even hunt the fry and consume them. 

Hence, to prevent this situation, bring the female to a breeding net or a different tank to separate the babies from larger fish. 

Adult Mollies

As long as you feed your fry quality food, they will grow up healthily. It takes about 1-2 months for the molly fry to grow big enough to move them back to the community tank. Based on the food and water parameters you provide, it takes about 4-6 months for fry to reach its adult-hood. 

A female molly can produce more than 100 babies in one birth. The breeding cycle takes 40 to 60 days. You will find an increase in belly size and spot when a female gets pregnant. Put the female in the nursery tank because the male tends to chase around and stress out the female. Stressed mollies might experience more aborted births and stillborns before the birth date. 

It’s a good idea to heavily plant the tank, giving female mollies and babies plenty of space to hide. 

Filtration and Temperature for Fry 

A sponge filter is a perfect choice for your fry’s tank. A powerful filter can suck the babies because they are not strong enough to handle the water current. 

Molly fry prefers a tropical temperature between 72 to 84 degrees Fahrenheit. You should include a high-quality heater and chance out the water regularly, providing the best condition for the fry to develop. 

Common Diseases

Aquarium fish are prone to ich – a disease caused by nasty tiny protozoa. There are symptoms of ich, including:

  • Twitching
  • Rubbing their bodies against surfaces of objects in the aquarium
  • White spots on the gills and body

Molly fish are also sensitive to swimming bladder disorders and diseases, mainly because they tend to overeat. They will have abnormal swimming patterns, distended bellies, and struggle to maintain buoyancy.

What’s more, your mollies might suffer from skin flukes and other parasites, fungal and bacteria infections.

Final Thoughts

Caring molly fish is a piece of cake. Molly fish are aesthetically-pleasing, social, and friendly aquarium fish species that can live harmoniously with most other community fish. 

If you’re new to the aquarium hobby, it’s worth bringing a stunning molly fish to the tank. As you’re a beginner, let’s make everything easy in the first place.

So which species of mollies will you introduce to your current aquarium? 



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