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Black Molly - The Black Beauty in the Aquarium

Today, we will take a closer look at a species from the Poecilia family. Although its Latin name might not mean much to you, most of our audience is very familiar with this family—mollies. Among the many colorful molly species in this family, there is one that stands out. Not actually a black sheep, but a black fish—the Black Molly.

In nature, black mollies can be found in Central and South America, along with other molly fish. The natural habitat of these tropical fish is mostly freshwater streams in South America. However, they have been observed in the ocean as well, sometimes adapting to brackish conditions. Despite this, they prefer freshwater habitats. The Black Molly is striking because of its unique color—completely black. Thanks to this, it adds an exciting contrast to any aquarium and stands out from its surroundings.

Moreover, it is an active, sociable freshwater fish suitable for a typical multi-species community aquarium. Community fish are also ideal tank companions as they eat unwanted algae. Although black mollies are not schooling fish, it is recommended to keep several individuals to ensure a comfortable life. In aquariums smaller than 100 liters (approximately 27 gallons), it's best to keep 4 males and 5-8 females. Males of this species become very territorial, so it is important to have more females than males even in larger tanks. The gender difference is easily noticeable. Males' anal fins are modified into a mating organ called a gonopodium. Additionally, male mollies are smaller than females, growing up to 10 cm in the aquarium.


Now, let's talk about the requirements of black mollies before adding them to your current stock. First, this species is sensitive to water temperature changes, so when introducing them to a quarantine aquarium (strongly recommended before adding to the general tank as fish may bring unwanted infections from the pet store), be super delicate. A quarantine tank is a separate aquarium where new fish should be kept to monitor for health issues. If you end up with a sick fish, the quarantine tank will prevent the infection from spreading to other fish. Depending on the illness, infected black mollies should be kept separate from other tank mates as long as symptoms are visible. Fish pox and protozoans are common diseases in black mollies. You can try treating them with aquarium salt baths, but do this in a hospital tank rather than the main tank.

For optimal development of black mollies, try to maintain a stable temperature between 24-28 degrees Celsius. They are tropical fish, so they prefer warm water. For substrate, gravel is recommended. Black mollies like hiding spots, so decorations like rocks and dense, fast-growing plants such as Anubias would be a good choice. We suggest adding some floating plants like Vallisneria for better arrangement.

On the other hand, they are active fish, so swimming space is essential. Luckily, black mollies like to swim in the middle and upper parts of the aquarium, making them visible almost all the time. The water should be well-filtered and oxygenated, with a pH of 7-8 and water hardness of 11-30 dGH. Poor water quality and unstable temperatures can cause severe health problems for black mollies, so ensure you have proper filtration and a heater if necessary.Black Molly Species | Tropical Fish Hobbyist Magazine

Characteristics and Feeding

Black mollies are also considered easy to care for when it comes to their diet. They clearly prefer plant-based food. Since black mollies mainly feed near the surface, they should be provided with light flake food that has a high vegetable content and doesn't sink too quickly. When choosing prepared food, look for ingredients that support the fish's immune system, as they are sensitive to temperature changes. It's worth investing in high-quality flake food containing Spirulina. Experienced aquarists can recommend the best brands of fish food. It's also important not to overfeed the fish. Excess food can harm the fish and disrupt the entire ecosystem in the aquarium, leading to issues like snail outbreaks or excessive toxins in the water. Some aquarists prefer to supplement black mollies' diet with frozen foods like daphnia.

Another benefit of keeping this species in your aquarium is that they love to eat algae. Like every cleaner fish, they have their preferences. Black mollies are very effective at cleaning green and brown algae as well as diatoms. Additionally, juveniles also consume blue-green algae, so if you're struggling with it, consider young black mollies as a solution. Adult fish prefer cleaning green algae, supplementing their diet with flake food.


If you want to breed mollies, as long as you maintain optimal water parameters including suitable temperature, aeration, and purity, breeding black mollies should not be difficult. Pregnancy lasts 4 to 6 weeks, resulting in 10 to 60 individuals. Black mollies are livebearers, meaning the female gives birth to fully developed fry capable of independent life. The fry grow quickly and are not difficult to raise. However, to avoid being eaten by other fish, the female should be separated from others—placed in a breeding net or a separate breeding tank. Black molly fry are very sensitive to toxins in the water, so the breeding tank should also be equipped with a filtration system. How to feed young black mollies? You can provide them with the same food as adult mollies, just chopped into smaller pieces.

As you can see, the Black Molly is a great fish for both beginners and experienced aquarists. As we always emphasize, this popular freshwater fish can join your cleaning team, helping to control algae levels and support the filter's work. It is a sociable fish that can be kept with almost any species requiring similar water parameters. In our opinion, the Black Molly is unique among other molly varieties. It stands out with its contrast to colorful tank mates and will be a real star in the tank.

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