a close up of a gold Molly with black spots all over their body

Mollies are a very popular fish for saltwater aquariums. Their bright colors and being easy to care for make them a top choice for many family’s. All species of Mollies are peaceful and pleasant fish, making them great additions to saltwater tanks with other peaceful species.

A Molly is a great fish to start with for your family’s saltwater aquarium. The Molly fish is a freshwater livebearer species that has adapted to life in saltwater aquariums, but studies have shown that the Mollies can’t survive in freshwater after having been conditioned in the saltwater environment. 

Mollies are a great choice for your aquarium because they are a schooling fish. They do best when there are at least 6 of them. They should be kept in a tank that has enough swimming space for the school to be able to move around.

These are one of the most popular fishes for less experienced families starting a saltwater aquarium. Mollies are hardy and are considered to be low maintenance. They do need places to shelter and reproduce. If your aquarium doesn’t already have plants consider adding some to their tank. Plants will mean extra lighting may be needed during the daytime.

They’ll live peacefully in a community setting for up to five years with a healthy environment. Families will enjoy watching schools of these fish swim, and the beautiful colors that they’ll bring to your family’s aquarium.

Information about Mollies

  • Average length: 2 – 4 inches
  • Fish Colors: White, golden, and black
  • Good Pet: Yes
  • Tolerance to Heat and Cold: Better cold than warm
  • Good with Other Mollies: Yes
  • Good with Other fish species: Only the peaceful ones
  • Good for Less Experienced Pet Owners: Yes
  • Health Concerns: Bladder disease, Dropsy, and Velvet disease
  • Average Life Span: 3 to 5 years

Physical Appearance of Mollies

a close up of a yellow Molly

Just like all other fish, Mollies have different subspecies due to crossbreeding. In home aquariums the most common Mollies are the short-finned Mollies and the sail-finned Mollies. There are other varieties that have originated from crossbreeding the two main varieties. Each of the Molly species is distinct from the other.

Temperament of Mollies

Mollies are a peaceful fish but can protect themselves when provoked by other fish in their tank. The males can also become aggressive when they want to mate and are known to chase females around the aquarium. 

Male Mollies also tend to fight other males in their tank to become dominant and gain the attention of the females. They can also become aggressive if placed in a small tank that is overcrowded. Mollies don’t enjoy living in crowded places and in frustration may nip the fins of other fish.

They enjoy swimming in small groups near the surface of the tank but when scared they go into hiding. Mollies mainly hide among the plants and near substrate.

Ideal Tank Mates for Mollies

Mollies give birth to live fish rather than eggs and they live well with other live-bearing fish. Here is a list of some of the best tank mates for your Molly.

Tank Conditions

Here are all the requirements you need to follow with your Mollies.

a close up of an orange Molly

Tank Maintenance

Replacing the water in your fish tank is the most important task because it helps keep the water in good condition. If your only fish is Mollies, all they need is about a 25 percent water change each month.
Before you do the water change it is a good idea to clean the walls of the tank using a brush and a sponge to scrape away any algae build-up. Then when the water change is being done, most of what was scraped off the tank can removed.

Tank size

A 10 gallon aquarium is the minimum tank size for your Mollies. If you have the bigger Mollies such as the Sailfins, then they should be living in a 30 gallon tank so that they have plenty of space to swim. Remember that they become aggressive if they feel cramped, bigger tanks are better for them.


Decorate the tank with many green plants so that your fish have enough shade and hiding areas. The Anacharis plant grows quickly and will create several hiding spots in your aquarium. Plastic plants can be a good alternative to living plants. Beautiful rocks, and caves also make a great decoration for the aquarium because the fish can hide out whenever they get scared.


Mollies love well lit aquariums and regular aquarium lighting is all that’s needed to create enough light in their tank.


2 Mollies swimming past each other near the bottom of an aquarium

A substrate made up of fine gravel, sand, or smooth rocks are best for these fish. The substrate should not be rough because you don’t want it to hurt your fish. The substrate is necessary because Mollies enjoy resting at the bottom of the aquarium especially at night.

Filtration system

It’s important to have a filter in your fish tank to eliminate harmful bacteria and food particles in the water. Mollies’ natural habitat is shallow and slow moving waters. A sophisticated or expensive filter isn’t necessary because it doesn’t need to create a current in the tank. A filter that cleans the water efficiently is all that’s needed.

Water conditions

Mollies do well in temperatures kept between 72 and 78° F and water pH of between 6.7 and 8.5. Having a thermometer and salinity testing kits can help you maintain these conditions at optimum levels.

Mollies are easy to care for and regular maintenance practices will help take care of their needs. The temperature and pH levels of the tank should be monitored regularly. The level of ammonia and nitrites should be kept as low as possible. Anything above can cause the Mollies to have certain health conditions like fin and tail rot.

Mollies create a high bioload in the water which requires regular water changes. Around 25 to 30 percent of the water should be changed each week to keep the water clean and healthy.

Attention Requirements for Mollies

2 sail-finned Mollies swimming together

Some types of Mollies have specific requirements that if not met may lead to the loss of your fish. Short finned Mollies make the best pets for beginners because they don’t require very large tanks.

If you have the larger Mollies, especially the sail-finned and the Lyretail Mollies, you need to have very large tanks. If you plan to have more than 1 of either of these types, plan to have a very large tank to hold them. 

They require enough space to swim, hide, and mate. Because of their space needs the larger Mollies aren’t the best for beginners because the cost of buying a large tank can be significant.

Other than space, it’s also worth noting that some Mollies are slow swimmers because of their body shape. The Balloon Molly and the Potbelly Molly have unique body shapes compared to other varieties of Mollies. 

If you plan on having these two fish, avoid filtration with very strong currents because it could end up slowly pulling these fish to the end of the tank with the filters.

Health Issues

The mollie found a diamond

Mollies aren’t susceptible to most fish diseases because they have quite a strong immune system. Either way, the fish can become ill if the quality of the water deteriorates or they have an improper diet. 

If you want to prevent your fish from becoming sick, it is very important to maintain optimum water conditions and cleanliness. Fish fed a well-balanced diet should get all the nutrients they need to keep healthy.

Other than cleanliness and diet, you can also protect your Molly from becoming sick by not overcrowding the tank. Overcrowding causes stress that eventually weakens the immunity of your fish. 

All new fish should be placed into a quarantine tank first before placing in your main tank. This isn’t always possible, so once you have your fish at home, look them over before adding them.  

No matter how much the temptation of handling your Molly may be, no one should ever touch the fish because you could pass on germs to your fish.

Here are some of the common diseases that attack Mollies and some of the ways you can prevent them.



The disease is dangerous and is identifiable by the following signs and symptoms.

  • Bulging eyes
  • Protruding scales
  • Bloating
  • Organ failure

Dropsy occurs if you expose your fish to very low temperatures in the water for a long time. Unfortunately the disease has no cure and the best solution is euthanizing your fish.

White Spot Disease

This disease may also be referred to as Ich and it occurs due to poor water conditions in the fish tank. A sick fish usually has difficulties breathing and may also be seen rubbing against plants and substrate in the aquarium. If you look at the fish, you’ll also notice white spots that look like specks of salt.

The good news is that the disease is treatable by simply improving the water quality. The first step towards treating the fish is raising the water temperatures to about 80 degrees Fahrenheit. The high temperatures kill the parasite making it fall off the skin of your Molly.

After raising the water temperatures, it is best to remove all non living plants and decorations from the tank because the parasite may remain on them. Then make a 25 percent water change and test to confirm that all the water conditions remain at optimal levels.

Adding a teaspoon of aquarium salt for every gallon of water also helps to control the White Spot Disease among Mollies. After two weeks, perform a 50 to 75 percent water change to completely eliminate the disease causing parasite.

Swim Bladder Disease

The swim bladder disease mainly occurs due to issues of overfeeding or constipation. A Molly with the swim bladder disease appears to have an extended stomach and seems to swim in a strange way, different from how other Mollies swim. For example the fish may swim upside down or move sideways.

To control the disease, stop feeding the sick fish for about 3 days to avoid aggravating the situation. If you’re feeding your fish on commercial pellets and flakes, moisten them in water before feeding the fish to reduce the chance of constipation.

The Molly Disease/ Velvet Disease

The Molly disease is highly contagious even to other fish in the tank. The disease is caused by a parasite called Oodinium and that thrives due to poor water quality. A sick fish appears to have a film of gold or rusty color that looks velvety. Other than the appearance, there are other signs and symptoms of the disease.

  • Fish loses appetite
  • Weight loss
  • Fins appear tangled
  • Fish rubs against surfaces
  • Skin peeling
  • Difficulties breathing

The Oodinium parasite thrives in light and the best control method is to dim the light in your fish tank. Also raise the water temperatures to the maximum your fish can handle, as the parasite does not do well in warmer waters. Adding a teaspoon of aquarium salt also helps to fight this fish disease.

Feeding Mollies

a pile of colorful fish flakes

Mollies are omnivores and can eat a variety of vegetables, plants, live and frozen foods. The main food for Molly is quality fish flakes that are available in the pet stores. Supplement your fish’s diet with vegetables. In the wild they enjoy eating plants and algae.

The best vegetables for Mollies are zucchini, spinach, and lettuce. Some dried algae is also a great choice to give your fish a taste of their natural food. Live or frozen Daphnia and Bloodworms are also great sources of protein for your Mollies.

Mollies are known to eat more than they really need to. To prevent overfeeding, only feed your fish two to three times a day on what they can consume within two to three minutes. Avoid having leftovers in your fish tank because they contaminate the water making it dangerous for your fish.

Related Questions:

How do Mollies Breed?

After mating, the female Mollies can keep the sperm in their body for about a month and use them even when there are no males in the tank. The gestation period of a Molly is about 60 days after which the fish can give birth to between 10 and 60 fries at once.

Baby Mollies can get eaten by larger fish in a community tank. Having dense plants like the Dwarf Hairgrass can give them a place to hide. The plant looks like grass for your aquarium where the fry can hide until they become bigger. 

Another option is to place a pregnant Molly in a breeding tank until she releases the fries. Once she gives birth, remove her from the tank and leave the young ones until they’re big enough.

Can Mollies and Guppies Mate?

Mollies and Guppies have a lot of similarities especially when it comes to mating. Male Mollies are also known to mate with any females in the fish tank especially the Guppy females. It’s not uncommon to find a Molly and a Guppy mating.

What Types of Water can Mollies Live in?

Mollies can live in freshwater, brackish waters, and saltwater. Most likely you’re familiar with the terms saltwater fish and freshwater fish. Brackish waters is a term that refers to a mixture of saltwater and freshwater. It is more saline compared to fresh water but not as much as salt water.

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Maryna is an animal expert that has had dozens of animals in her life over the years. She has never found an animal that she didn't love immediately. It seems like every year she finds kittens that have been abandoned by their mom and she nurses them to health and finds homes for them. She contributes her vast knowledge about animals and family pets to our website and we're forever grateful to have her working with us. She's also an amazing graphics designer and has designed all of the social media images that we use across all platforms.