Black Molly Fish – Habitat, Care, Feeding, Tank Size, Breeding

The Black molly is a quite unusual fish, as it is born with a severe case of melanism. This skin condition describes the lack of pigmentation, meaning that the fish is entirely black.

The black molly is a result of the hybridization of the Sailfin Molly and the Common Molly. Black molly populations are, therefore, rare in the wild.


Black mollies are fairly small in size, and will generally measure between three and six inches in length. Females grow a couple of inches longer than males.

The entire body of the fish is black, although some can have a slight silvery hue on the flanks or a yellow stripe stretching down the dorsal fin. Most individuals display round fins and a flat coloration on the scales.


The two species that were bred to result in the black molly inhabit fresh, brackish, and salt habitats. The Sailfin Molly occupies brackish channels in Florida, Virginia, California, and Texas. Black mollies have no natural populations and are mostly found in household aquariums.


Black mollies are omnivorous, and they accept detritus, plant matter, and invertebrates. High-quality flake meals should make up the base of their diet.

Supplement these flakes with frozen or live foods like daphnia, blackworms, bloodworms, mosquito larvae, and brine shrimp.

You can provide your mollies with small vegetable portions like zucchini, lettuce leaves, and cucumber once or twice a week. Black mollies will also consume the algae in your aquarium and help to keep it clean.

Water & Tank Conditions


Tank Size

It is advisable to keep the black mollies in a spacious tank since they demand stable water parameters. The minimum aquarium size for a small group of mollies is 30 gallons.

You will need at least 45 gallons if you intend to breed them and raise the fry to a reasonable size.

Temperature and PH

Black mollies thrive in a temperature range of 70-80ºF. You will need a high-quality heater to maintain this range. The optimal PH range for black mollies is 7.5-8.2.

Water Conditions

Black mollies are sometimes mistaken for brackish water fish, but they thrive best in freshwater setups. Some forums recommend adding salt to an aquarium with black mollies, but studies show that the fish will be happy in a tank without salt.

The practice is also not ideal if you keep the mollies with other freshwater fish since the added salt may harm the other tank’s residents. You can add salt if the mollies live alone or if they are in quarantine.

The fish are intolerant of poor water quality, which is why you need a big tank for them. The tank should be fitted with an effective filtration system to maintain ideal water conditions.

A canister filter is a powerful option, but it tends to be overkill with the fish and is quite expensive. Your aquarium will do with a simple hang-on-back model.

Since black mollies will not mind air bubbles, you can include an air pump setup to promote aeration. Sponge filters function as air stones and filters, and they are common in aquariums with black mollies.


Black mollies appreciate planted aquariums, and adults will especially feel comfortable in such a setup. The plants will also boost the fry survival rate since mollies are known to feed on their young ones. You can keep mollies with water sprite, Java Moss, Java Fern, Amazon Sword, water wisteria, and Hygrophila.

Black mollies swim in the middle part of the tank, so keep this portion open when decorating the aquarium.


Be keen on the ratio of black mollies that you keep in your tank. Not only are males known to be aggressive towards each other, but they can harass females as well.

Keep three females for every male to ensure that no one female gets all the attention from males. The males can relentlessly pursue a female to mate, and the female can get stressed and even die.

You can keep black mollies with similarly-sized fish. They get along with guppies, platies, gouramis, tetras, danios, swordtails, endlers, white cloud mountain minnows, and female bettas.

The black molly is generally peaceful, but it can exhibit a level of aggression in a small and crowded setup. If you keep black mollies with other livebearers, ensure they are plenty of plants for the fry to hide.


Black mollies are live-breeders, and reproduction will generally unfold on itself. You should let the mollies breed by themselves by ensuring they are more females for every male.

During mating, the male molly utilizes its gonopodium to ejaculate to the female and hook closer to her for successful copulation. You can tell the female molly is pregnant if you notice a significantly plump stomach and a dark gravid blotch close to the anal fin.

Some aquarists prefer to remove the female to a ‘nurser’ aquarium before they give birth. This is done to tame the aggression of the male since they can continue to pursue the female to continue copulating.

You can also use an aquarium net breeder to separate the mother if you choose to leave her in the main aquarium.

The female carries the eggs for around 35 to 45 days, and they can lay up to 100 hundred juveniles if they are large in size.

The juveniles emerge rather large in size, and they hide among the plants at the bottom for a while. Mollies commonly feed on their fry, which is your tank needs to be densely planted and decorated.

The juveniles will feed on similar foods as the adults, so you should provide high-quality flake foods. Provide the fry with live or frozen black worms, blood worms, Grindal worms, brine shrimp, and daphnia.

You will be able to tell the males and females apart after about two months, and you can separate the two genders to discourage breeding. Black mollies reach sexual maturity after about eight weeks old, and they can breed between siblings.


Black mollies have an unusually dark body, which has been brought about by captive breeding.

The fish will contrast well with a light substrate and the rich green color of plants like the Java Fern and Anubias.

The black molly is generally peaceful if kept in a large tank, and it has many potential tankmates.

Updated: February 24, 2020

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