Black Molly Care – A Complete Guide

The black molly is a specie of mollies, that are also livebearers. However, it is one of the most common fish that most aquarists usually care for. This is because they are hardy and easy to keep.

Black mollies are distinctly known for their unique color and display. Just like many fish, black mollies require similar care and treatment for up keeping.

In this article, we will delve into how you can care for black mollies, even as a beginner. Moreover, we will discuss other factors, such as, feeding habits, water conditions, temperature, and others, that can influence the well-being of black mollies.


The black mollies, which belong to the family, Poecilia sphenops, are small species, that are also called livebearers. That is, they do not lay eggs. Also, they are one of the top-ranked fish in home aquariums. Black mollies are native to Central America, and Black America. Also, they exist in areas like Mexico in the north, and Venezuela in the south. You can also find on several Caribbean islands.

However, in recent years, they are popularly found in some areas in the United States, Japan, and a few parts of Eastern Europe. Moreover, mollies’ primary habitat is in freshwater streams, but they can also survive in brackish water and swamps. However, it is rare to find black mollies in the wild, because its unique color is mostly a result of captive breeding.

Black Molly Habitat

The most important factor you should consider is providing a spacious aquarium tank for your fish. In most cases, black mollies are sensitive to water conditions. Whereas, a large space will help stabilize and maintain a constant water condition.


Black mollies derive the name from their unique black color. Unlike other mollies, they are often completely black. That is, many of them have no spot of another color on their body. Including the fins, and eyes. However, not all black mollies are completely black. As you may see a streak of yellow line that starts from the head to the dorsal fin. Also, you may see some silver spots on the flanks of some black mollies.

Black Mollies Size

Usually, female mollies are often larger in size than the male gender. Females grow to an average of 5 inches (12.5cm), while the males grow up to 3 inches in length. Generally, black mollies are small in size, and the male mollies grow at a fast rate initially. But female mollies eventually exceed them in length.

Black Mollies Tank Condition

Generally, black mollies are beautiful creatures, but they can be aggressive in some situations. Because of this, you need to watch out for the ratio of females and males to put in a tank. As males can be aggressive towards each other when you place them together. Also, when the males outnumber the females, the female gender is usually harassed.

Moreover, some have argued that black mollies thrive best in brackish water. Which is not completely true. As they can survive in almost every water condition. However, it pays off even when you keep them in freshwater tanks. More importantly, the size of your aquarium tank matters. Therefore, you should keep them in a tank large enough to enable them to move around freely. More so, you should keep them in at least 20-gallon size. Whereas, a bigger galloon will be better.

As regards the PH and water temperature for your black molly fish, the appropriate water condition for keeping your black mollies should be between, 70-80°F, with an alkaline PH of 7.5-8.2. Moreover, you must be consistent with the water condition. Also, black mollies like having decorations in their tank. You can add rocks, and plant more plants in their tank, to enable them to thrive more in the aquarium.

However, lots of plants in the aquarium tank may not be comfortable for adult mollies, but it is a safe and hiding place for fry. Also, they can be a hiding space for weak mollies. Besides, any aquarium plant will be suitable for your tank, but here are few plants you should add to the tank. These include, Amazon Sword, Hygroplila, Java Moss and Java Ferns.

Are Black Mollies Aggressive?

Black mollies are one of the peaceful fish that exist, among others. As they are widely kept by many aquarists based on their non-aggressive nature. However, their male gender can be somewhat aggressive. Usually, the aggressive trait of males’ surfaces when they are fighting for dominance or territory with other males in the tank. However, if your tank is big enough to accommodate every black molly you intend to keep, then no harm will happen to any of them.

Apart from this, male mollies tend to display an interesting sight when they are about mating with the female gender. However, if you notice frequent fights between fish, you can add some decorations such as rocks and plants in the tank. These decorations will serve as shelter for the fish that is being bullied. Generally, black mollies are a good option for your community tank.

How Long Does a Black Molly Fish Live?

Most black mollies live up to 5 years of age. However, their lifespan is mainly dependent on how well you care for them. This covers their environment condition, feeding habits, and tank requirements. However, some fish keepers have complained about their molly baby fry not grow to adulthood. This is true, as adult mollies are likely to eat the fry. Even the mother is not an exception in this. But, you can prevent this from happening, by separating the mother. More details as regards this is further explained.

Also, black mollies fry can be short-lived because of their parent’s’ incompatibility. During the breeding process, ensure you are choosing the right pair of opposite sexes to mate together. However, some fish keepers tend to mate black mollies with guppies. Technically, you can achieve this. But the fry may end up being sterile.

Do Black Mollies Need a Filter?

Although, how much you can afford also influences the equipment you make available for keeping your black molly. However, some basic things are quite affordable, which you must place in your aquarium tank. A filter is one of these tools you should install in your tank. Whereas there are a lot of filters you can choose from. However, we recommend that you choose a filter that will provide a smooth surface. Because black mollies love to swim around the tank surface.

How Often Should I Feed My Black Molly?

Feeding black mollies is a simple thing. As they have a wide variety of food options, and they eat almost everything you offer them. Moreover, black mollies can help clean your tank, because they are good algae eaters. Also, try feeding your molly’s natural food products as much as possible. Because mollies are omnivores, they love eating small invertebrates, plant matter, and some detritus.

Majorly, black mollies need green vegetables in their diet to survive. You can either choose from cucumbers, zucchini, and shelled peas. However, you should endeavor to feed them vegetables twice a week. Also, you can improve their diet diversity by including flake food in their diet. You should also include supplements like black worms, bloodworms, brine shrimp, and daphnia.

As regards the number of times to feed your mollies, black mollies are voracious eaters. And if you permit them, they can eat within 5-minute intervals. However, they won’t mind eating twice or once daily. Which is quite acceptable. Also, avoid feeding them too much at a time. We recommend that you feed them little food at once. Moreover, adult mollies can live for days without eating. But ensure you are not starving them instead.

Breeding Black Mollies

Generally, if you place female and male in the same tank, with three females to one male ratio, the breeding process will occur itself. Moreover, mollies are sexually mature at an early age. Such that, the females can release fry within a couple of months. However, the breeding process will be faster if you set up the fish tank appropriately. Also, some fish-keeper prefers moving the female molly into another tank. This is done to enable the separation of the mother from her babies after birth. However, it is better to wait until the female molly is close to releasing her fry before you put her in another tank. This will help reduce the risk of miscarriage.

If you ever wonder why we recommend you separate the pregnant molly, it is because of the bad parental care of adult mollies. Therefore, using a breeding box will allow the fry to escape into a “nanny” tank, while the mother remains trapped inside.

Moreover, mollies can give birth to a large number of fry, ranging from 40-100 fry at once. Although, the number of fry they release is sometimes dependent on the age of the parent. However, the gestation period often takes place between 6 to 8 weeks. While in rare cases, the gestation period takes place in just 4 weeks. As regards the care for black mollies fry, they require no special treatment. Whereas, they can survive in the same tank requirement. And concerning their feeding, they eat the same type of food just like adults. However, their food should be more grounded, and smooth, for easy digestion. Moreover, the frequency of feeding mollies fry quite differs. To ensure their full development, you should feed your fry at least 3 times per day.

Do Black Mollies Need a Heater?

Just like every other molly, black molly needs a heater in their aquarium tank to survive. As black mollies are very sensitive to change in water conditions, the absence of a heater will make them easily stressed out. Also, a heater will help keep the water temperature and PH steady. Moreover, most aquarium heaters are automated. So, it is quite easy to use. As for the PH level, we recommend you get a PH testing kit to check the tank PH condition.

Are Black Mollies Fin Nippers?

Black mollies are known to nip at the fins of other fish. However, they don’t usually do this at a dangerous level. As they naturally prefer to keep to themselves. Moreover, there have been no reported cases of black molly fighting with another fish in the same habitat. Some mild fin nipping is the only molly act you may want to be concerned about. Because they nip at the other tank mates. But as long as you watch your fish closely, you are good to go. However, mollies have a hierarchy order. And they display this act of honor in a civilized manner. Although, only if you are very observant will you notice this among your molly fish.

Do Black Mollies Eat Other Fish?

The peaceful nature of black mollies cannot be overemphasized. Not only do they keep to themselves in a community tank, but they are also a good choice for starter fish in your home aquarium. Black mollies do not eat other fish. However, the bad parental attitude of mollies towards their babies is what you may want to be concerned about. Because, your molly may end up not having any young specie to leave behind.

Black Molly Fish Tank Mates

Black mollies are fish that can live successfully with other species in a community tank. However, as peaceful as they are, there are exceptions to this. As some big predators may be a threat to the life of your gentle molly. So, based on popularity, here are some fish that have been successfully kept with black mollies. Danios, Guppies, Tetras, Swordtails, Platies, Gouramis, female Betta fish, and other mollies.

In conclusion, knowledge is key in setting up an aquarium tank for your black molly. If you follow all the measures mentioned above, you can be sure to be a successful fish-keeper. Especially if black molly is the starter fish. As you can easily care for them, and expect them not to be a threat to another type of fish.