Black Molly Care Guide – Diet, Breeding & More

Black Molly portrait

If you are looking for a new fish to put in your aquarium, the Black Molly is certainly a good option to consider. 

While this fish isn’t the brightest or most colorful, they are still very elegant and desirable as a pet.

Black Molly Appearance

The reason that Block Mollies are born completely black is because of a condition called melanism. Some of these fish do have a bit of yellow across their dorsal fin, but most of them are totally black. There are even some cases of a little silver coloration on the flanks of these fish, though it is fairly uncommon.

These fish can grow up to three inches, but the females tend to be a little bigger than the males. They have an average lifespan of around five years if properly taken care of.


While the Black molly is known for being pretty peaceful in general, they can be very aggressive when kept together. They really enjoy swimming around and are generally active as long as they remain healthy.

Natural Habitat

The Black Molly has no natural habitat per se, as they are a result of selective breeding. They are most likely descended from fish that were native to Central America and South America.

Black Molly pair in aquarium e1580762468566

Black Molly Care Guide

1. Tank Setup

It will be necessary to have a minimum 20-gallon tank if you want to keep Black Mollies. The larger the tank is, the better these fish will do. They do well in freshwater tanks with lots of plants and places to hide. The latter is particularly important if you plan on breeding these fish.

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2. Water Conditions

You will need to get the water in your Black Molly’s tank between 70 and 80 degrees Fahrenheit with a pH of 7.5 to 8.2. Water hardness of 20 to 30 dGH is recommended for these Mollies.

Keep in mind that these fish can respond in extreme ways to even the smallest changes in their water. This is why it’s so important that you keep all of the water conditions as stable as possible on a daily basis.

It is also crucial that you change out about ¼ of the water in the fish’s tank each week. This will minimize the likelihood of illness due to ammonia or nitrates. These fish can quickly become seriously ill from such compounds, so you need to keep that in mind.

3. Black Molly Food

You can give your Black Molly just about anything to eat. They tend to enjoy live, frozen, and synthetic foods. Algae and other vegetation will help your fish get all of the nutrients it needs to stay healthy over the long term. These fish tend to eat a lot of algae out in the wild, so you should provide them with plenty of it in their tank.

If you are going to get flakes to feed your fish, make sure they are specially formulated for Mollies. You can also give them certain vegetables like leaves of lettuce, cucumbers and squash. Some of this food should be boiled before so it is edible for your fish. Veggies make up a relatively small but important part of this fish’s diet, so you don’t want to skimp on them.

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It is important to spend some time looking for high-quality fish food to give your Black Molly. Proper nutrition is crucial for keeping these fish healthy so they live as long as possible. You can also give them microworms and brine shrimp. A balanced diet will provide your fish with all the nutrients it needs to stay healthy over the long term.

Black Molly swimming

Common Health Problems

Black Mollies are susceptible to the same diseases and illnesses that most other Mollies are. This includes parasites, fungal infections, fin and tail rot, and dropsy. Some of the signs of these conditions include slowed reactions, spending an unusual amount of time at the bottom of the tank, appearance of raised bumps, pale gills, and bulging eyes.

You can drastically reduce the likelihood of bacterial, fungal and parasitic infections by maintaining proper water conditions for your Molly. This will go a long way towards keeping them healthy as a whole.

Black Molly Breeding

You can easily tell which sex your Black Mollies are by simply observing their size. Females are almost always larger than the males, and they have a rounded abdomen. The anal fin of the male fish is tube-shaped, and the females has a triangular appearance.

Unlike many other types of fish, Mollies are live breeders. It can produce up to 100 fries with a single birth. Their offspring are not hatched but produced live by the female. One of the great things about breeding these fish is that you don’t have to fret over special tank conditions. It is fairly easy, provided you know what you are doing.

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Make sure that you keep a close eye on the males and females after putting them together in the same tank. This whole process can last up to eight weeks, though there have been reported cases where it lasted only a month.


  • Black Mollies are generally peaceful fish that tend to be quite active most of the time.
  • These fish are usually entirely black, though they can have traces of silver or yellow on their body.
  • It is a good idea to keep these Mollies in a minimum 20-gallon tank, but larger is always better. They need lots of room for swimming due to their active nature.
  • Keep the water in the tank between 70 and 80 degrees at all times.
  • Sudden changes in water conditions can result in illness or even death with these fish.
  • Make sure that you get a high-quality flake food that is formulated especially for Mollies.
  • You can also give these fish various vegetables and live food like brine shrimp and microworms.
  • Breeding Black Mollies are very easy and don’t require a separate tank or any special conditions whatsoever.