Molly fish are playful, cheerful and very entertaining. They’re a fun addition to any aquarium: beautiful, active, and playful.

Usually, they are also very easy to breed and care for. We’ll talk about their common characteristics, advantages and disadvantages of breeding them, the steps to breeding and caring for mollies and, finally, some tips and warnings.

Characteristics of molly fish (molly fish care pt. 1)

Mollies are viviparous fish (not laying eggs) which is ideal for collective or individual aquariums.

A single female can breed up to 100 larvae in a single pregnancy. Mollies come in a wide variety of colors and present no problem with other types of fish. To raise these minnows without any worries, just take the necessary precautions and prepare the aquarium well.

Some fish species, as we know, are not peaceful at all and cannot share space in the aquarium with different ones, but this is not the case with mollies. Mollies live very well with other species. However, if you want to breed mollies, you have to mix them with fish from other species.

Despite being a freshwater fish, this species is very adaptive to hot and freshwater. Mollies are very common in aquariums. However, in the wild, they are found in saltwater in lakes, estuaries, and rivers.

There are several variations of this species, such as the balloon, tiger and the most common is the black molly.

The good news is that a black molly, for example, can live in the aquarium for at least eight years. Mollies in general live between 2 and 3 years on average and are approximately 6 inches long. Mollies’ larvae develop within the female and are born only when they are fully formed.

The advantages of having a molly in the aquarium (molly fish care pt. 2)

1. Their beauty

The molly’s beauty is the main reason most people like having them in their aquariums. It’s impossible, even among many other fish, not to notice the presence of this nice pet in the aquarium. A molly gives even more charm to aquariums that have fish of other species, because it makes the environment more charming and cheerful.

2. Playfulness

Some of the characteristics of this species include playfulness, agitation, and cheerfulness. Inside the aquarium, a molly will be ready to explore every corner and every space. One of the things they love to do is spend a lot of time in the background looking for algae. They also look for it in the ornaments and in the aquarium glass itself.

3. Ease of reproduction

Another advantage of having mollies is how easy breeding is. Even in captivity, reproduction is quite simple; just put a male and a female in the same aquarium. The gestation period of the females is around 21-35 days. They can store sperm in their bodies for several months, so they can even fertilize their eggs in the absence of a male. We also wrote a more in-depth article all about breeding mollies.

4. Ease of care

Another advantage of this fish is that they require a low level of care. For those who have never had an aquarium before, it is a good choice to start with this species.

The disadvantages of having a molly in the aquarium (molly fish care pt. 3)

1. Poor molly-to-molly relationship

Remember what we said about them living together with other species? They have a great relationship with other fish, as long as the other fish are not mollies. However, when they see fish of the same species, they leave the playful side aside and become aggressive.

So, if you still want to put more than one molly in a tank, the tip is to have more females than males, since males are more aggressive and tough.

2. Their reproducibility can be a downside

What is an advantage can also turn into a disadvantage. If the owner of the aquarium doesn’t take great care in managing their reproduction, this could result in an overcrowding problem. To learn more about managing their reproduction, check out our article on breeding mollies.

Guide to raising and caring for mollies (molly fish care pt. 4)

1. Buy an aquarium

You will need a 15 gallon to 30 gallon tank (55-115 liter) with 15ml to 30ml of water. Generally, a molly does best with a large and spacious aquarium. A small tank provides a number of problems: 

  • It provides less space for the fish to escape the aggressive ones, which makes them stressed.
  • It is harder to clean, which can make the fish sick.

2. Decorate the interior of the aquarium 

Give preference to stonesdecorative gravel, and air filters. Although they need space, mollies also enjoy obstacles to hide from more aggressive fish. The quieter minnows (baby mollies) often swim around the aquarium, fleeing the violent ones, and can get nervous if they have no place to hide.

3. Place freshwater plants under the substrate

The substrate serves as soil for the aquarium but can also be a source of nutrients for aquatic plants. It must be composed of two layers:

  • The top should be two-inches thick and may contain sand, gravel, rocks or pebbles.
  • The lower should have between one and two-inches of some nutrient-rich material. 

4. Fill the aquarium almost with water 

Ideally, leave only two-inches of space between the water and the mouth of the container. As mollies are tropical fish, the water should be warm (77°F-86°F) to make them very comfortable. Do not let the aquarium overflow or fill it with cold water.

Maybe you need an aquarium heater. Change the water at regular intervals. It is recommended to change a little water each day or 30% of the water per week. 

5. Feed them

feed them algaeMollies love eating micro worms, black worms, and blood worms. Feed them fish flakes (artificially processed thin layers of food) to give them a variety of nutrients. 

Frozen or live brine shrimp are also great sources of nutrients for adults and fry. 

If you can feed them algae, that’d also be great. Mollies normally eat algae in the wild.

6. Don’t use aquarium salt

Some mollies are brackish fish, which means they need varying amounts of fresh and saltwater. However, there is still no consensus on the use of sea salt in aquariums. Some experts argue that most mollies never come into contact with salt or brackish water and therefore do not need salt. 

Some sources recommend using approximately one tablespoon salt for every 20 liters of water. 

Adding salt can also help recover water if it is slightly soiled. 

If you buy an exotic type of molly, talk to a specialist about whether or not the fish needs salt.

6. Install the aquarium’s filter according to given instructions 

The water should have a neutral pH (7-8). Some experts recommend slightly increasing the pH to 8.4. You may need to adjust the filter and water after the aquarium is full.

7. Finish an aquarium cycle before placing the fish in the water

It is very important to let the aquarium undergo a complete nitrogen cycle so that the water acquires benign and beneficial bacteria, which protects the fish from disease. Completing a cycle depends on the water’s temperature. Based on the temperate, you should be keeping for your mollies (77-86°F), this will take two weeks.

In the case of an aquarium for mollies, it’s not recommended to cycle the tank with the fish. They will most likely not survive the exposure to lethal nitrites and ammonia.

How to cycle the aquarium without the fish

Cycling the tank without fish is more humane, recommended and safe. Here are the steps:

  1. Drop some fish flakes about twice a day at regular intervals in the water. 
  2. Wait for the dropped feeds to decay, turning to ammonia in the water. 
  3. Every other day, get a water test kit and measure the level of ammonia. It must be above 3 parts per million (PPM). If it gets lower, add more feeds to develop more ammonia. 
  4. Few days after, this process will initiate the growth of Nitrosomonas, which will eventually eat up the ammonia. But keep adding more fish flakes so the water doesn’t go below 3ppm until about a week at least.
  5. After a week of this continuous practice, test for nitrites in the water by using any commercial test kit. An example is the Tetra 6-in-1 Test Strips or the API Aquarium Test Kit. After the water test, the detection of nitrites signals the beginning of the nitrogen cycle. 
  6. What’s next is to keep adding ammonia (the feeds which then decay), keeping the right PPM, and testing for nitrites and ammonia. 
  7. About a week after you start checking for nitrites and ammonia, the levels of these substances will start reducing. This is the time to test for nitrates. 
  8. Once the levels of nitrites and ammonia drops to zero, that indicates the completion of the cycle. But still, your nitrate level must not exceed 40, or you’ll need to drain and add some water to reduce the reading. 

Now that the cycle has been completed, the water is set for the Mollies. 

8. Choose the number of mollies in an aquarium

Normally, it is best to place only two mollies for every 10 gallons (40 liters) of water. Mollies need space to swim and to hide from aggressive fish. If you want to increase the number of fish, you should use a larger tank.

9. Buy a molly 

There are several types of molly, it is super easy for them to cross-breed. Regardless of color, the fish are of the same species and males and females make no distinction. Some experts recommend that you buy molly subspecies if you want the fish to reproduce faster. To learn more, ask a store employee for help or do a search on your own.

Male mollies have a gonopod, a long, spiky fin on the underside of the body that serves to fertilize the female. 

Females, on the other hand, have a softer fan-shaped anal fin also on their lower body. 

10. Put the mollies in the aquarium 

Leave the bag containing the fishes in the aquarium for about 10-minutes to bring the water to the same temperature. Then release the fish with the help of a small net. 

Warnings (molly fish care pt. 5)

  • Do not turn the water from the bag into the aquarium.
  • Feed the other fish before putting the mollies in the water so that they do not think they are meant to be eaten.  
  • Be careful not to let the water get cold or overheat when you take the fish home. Do not leave them in the plastic bag for a long time before placing them in the aquarium.

As you can see, it is very simple to have a molly in the aquarium and take care of them. Just keep the water in good condition, in terms of the temperature, pH, and cleanliness. Then ensure proper separations are made for breeding and compatibility sake and everything should be a breeze.