Mollies are a very popular fish for saltwater aquariums. Their bright colors and easy care make them a top choice for many aquarists. 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 been adapted for life in saltwater aquariums, but studies have shown that the molly fish can’t survive in freshwater after having been conditioned in the saltwater environment for long periods of time. 

Mollies are a great choice for your aquarium because they are a schooling fish, so you should always get at least 6 of them, and 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 beginner hobbyists.

Mollies are hardy and are considered to be low maintenance. They do require places to shelter and reproduce. If your aquarium doesn’t already have plants consider adding some to the tank. Plants will mean extra lighting may be needed during the daytime.

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

Information about Mollies

  • Average length: 2 – 4 inches
  • Fish Colors: White, golden, and black
  • Good Pet: Yes
  • Good with Other Mollies: Yes
  • Good with Other fish species: Only the peaceful ones
  • Suitable for First-Time fish Owners: Yes
  • Health Concerns: They tend to have swim bladder disease, Dropsy, and Velvet disease
  • Average Life Span: 3 to 5 years

Physical Appearance of Mollies

Just like all other fish types, Mollies exist in different varieties due to crossbreeding. In the aquarium setup, 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. 

Here is a guide on some of the most common Mollies for the aquarium.

Black Mollies

Black Mollies are totally black in color but some have a yellow tinge running down to their caudal fins. The black colors of this fish have a velvety texture making it a unique and beautiful fish.

Short-finned Mollies

The short-finned Mollies are also known as the Common Mollies and are characterized by dull silverfish colors.

Lyretail Mollies

These Mollies have fins similar to other Mollies except for the tail fins that appear to be very long forming a lyre shape. These varieties tend to lose the long tail fins and lyre shape as the fish ages.

Balloon Mollies

The Balloon Molly fish was captive bred and has a unique golden white color. The fish also has a very short and round body. During breeding, the fish developed a curved spine which tends to reduce the lifespan of this particular Molly fish. The curved spine greatly interferes with the internal organs of the pet.

Sail-finned Mollies

These varieties of Mollies are gray in color with white spots that almost look like stripes. The fish has an elongated body and the males have extra-long dorsal fins.

Dalmatian Molly

This variety of Mollies has a silverfish color with some black spots.

White Molly

Just like its name, this fish is purely white in color.

Golden Molly

The golden Molly has a golden color and is at times referred to as the “24 karat” fish.

Temperament of Mollies

Mollies are a peaceful fish but can at times protect themselves when provoked by other fish in the tank. The males can also become aggressive when they want to mate and may be seen chasing the females around the aquarium. 

Male Mollies also tend to fight other males in the tank in a bid to become dominant and gain the attention of the females. The fish may also become aggressive if placed in a small tank and in large numbers. Mollies don’t enjoy living in crowded places and in retaliation may nip on the fins of other fish.

The fish enjoys swimming in small groups near the surface of the tank but when scared they go into hiding. The fish mainly hide among the plants and substrate in the aquarium.


Tank Maintenance

Replacing the water in your fish tank is the most important task because it helps maintain the water in good condition. If your only fish is Mollies, all they need is about a 25 percent water change each month. Mollies don’t release a lot of bio waste compared to other fish types so small water changes should be fine.

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 buildup. Then when the water change is being done it can remove most of what was scraped off the tank.

Water conditions

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

In the wild, Mollies have been found to adapt well to a wide range of conditions. The suitable temperature for them is in the range of 72 to 78F. The pH level should be around 6.7 to 8.5.

Standard lighting equipment should be installed for the tank. They do not require any special types of equipment like air or water pumps. This is because they prefer slow moving water which would be provided by the outlet of the filter installed inside the tank. 

Mollies are easy to care and regular maintenance practices will help to 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 have a high bioload which would require 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

Some varieties 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 large sized Molly fish 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 you should plan to have a fairly large tank to hold them. 

The fish require enough space to swim, hide, and mate. Because of this, the large-sized 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. For example 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, you have to consider the filtration system to use. Avoid filtration with very strong currents because it could end up slowly pulling these fish to the end of the tank with the filters.

Tank Conditions

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

Tank size

The minimum tank size for your Molly is a 10 gallon aquarium. If you have the bigger Mollies such as the Sailfin variety, 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, so bigger tanks are better for them.


Decorate the tank with many green plants such as the Anacharis which grows rapidly to offer your fish enough shade and hiding areas. You can also buy plastic plants as an alternative to live plants. Crevices, beautiful rocks, and caves also make a great decoration for the aquarium because the fish can seek comfort whenever they get scared.


Mollies love well lit aquariums and they will be much happier if moderate amounts of lighting are installed on the top of the tank.


Mollies love a substrate made up of fine gravel, sand, and smooth rocks. The substrate should not be rough so that it doesn’t hurt your pet. The substrate is necessary because Mollies enjoy resting at the bottom of the aquarium especially at night.

Filtration system

It’s necessary to have a filter within your fish tank to eliminate harmful bacteria and food particles in the water. The Mollies originated from shallow and slow moving waters. Because of this you really don’t have to have a sophisticated filter that allows current in the tank.


Health Issues

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, here 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.

Best Tank Mates for Mollies

Since Mollies give birth to live young ones rather than hatching eggs, the fish lives well with other live bearing fish. Other than fish, Mollies can also live with other creatures that dwell in the water. Here is a list of some of the best tank mates for your Molly fish.

fish flakes

Feeding Mollies

Mollies are omnivores and can feed on a variety of vegetables, plants, live, and frozen foods. The main food for Molly fish is quality fish flakes that are readily available in the pet stores. Also supplement the diet of your fish with vegetables. In the wild the fish 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 easily 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 the 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 10-60 fries at once.

Baby Mollies can get preyed on by larger fish in a community tank. Having large plants such as java moss can give them a place to hide. The plant grows to become very big with wide leaves 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.

Can I switch Mollies from Freshwater to Saltwater or the other way? 

Yes, some Mollies can be switched between water types to fit your aquarium needs. This is best done with an acclimation period where you slowly increase/decrease the salinity of the water.  If done over the span of about four hours you will have them ready for life in new waters. 

Some of the Molly varieties that do well in salty water are those in the Sailfin category. The reason why the sailfin Molly survives when removed from a freshwater tank to a salty one is because this variety is not easily susceptible to diseases or stress. 

How to acclimate a fish from freshwater to saltwater?

The easiest way to get them ready for the new water type is to leave them in the bag they came in from the pet store. Place this bag at the edge of the tank and clamp it so that it does not move or sink when you open the bag.

Once the bag has been opened scoop some water from your established tank into the bag where your new Mollies are. If you add about 10 – 15 percent to the bag every 30 minutes after four to six hours you will have a fish ready for its new life.

At this point you can empty the water and the fish from the bag into the tank.

Can All Mollies Switch Water Types?

Not all Mollies can survive if moved from freshwater to saltwater aquariums and vice versa. Only the sailfin and giant sailfin Mollies have been known to survive the changes from the different experiments conducted by different aquarium hobbyists. 

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