Information, Freshwater fish, Live-bearers and killifish, Mollies, Species

Black Molly (Poecilia sphenops)

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by Jason Matthews



The Black Molly is a resilient and adaptable fish with a distinct, sleek appearance that distinguishes it from other fish species. They are simple to care for and appropriate for novice and intermediate pet fish owners. 

This article will look at the Black Molly’s origin, appearance, size, behavior, tank conditions, tankmates, diet, breeding, and diseases. Whether you’re a seasoned pet fish owner or just getting started, this article will give you everything you need to know to keep your Black Molly healthy and happy.


Scientific Name: Poecilia sphenops
Common Names: Black Molly
Life Expectancy: 3-5 years
Adult Size: 3-4 inches


OriginCentral America
Care LevelEasy
Tank LevelAll levels
Minimum Tank Size10 gallons (37.9 liters)
Water pH7.0-8.0
Water Temperature70-80°F (21-27°C)
Water HardnessModerate
Tank MatesPeaceful fish

Fun Fact Corner

One interesting fact about Black Mollies is that they are livebearers, which means they give birth to live young instead of laying eggs. Unlike many other fish species, the young are born fully formed and capable of swimming and feeding independently. 


The Black Molly, known scientifically as Poecilia sphenops, is a freshwater fish native to Mexico and Central America. It is thought to have originated in the warm, slow-moving waters of the Gulf of Mexico and nearby rivers and streams. The Black Molly has been selectively bred and hybridized, resulting in various color morphs and patterns. 

Appearance & Size

The Black Molly is easily identified by its sleek body and flowing fins. They have a streamlined, elongated shape that allows them to move through the water quickly and gracefully. Their bodies are usually solid black or black and silver, but selective breeding has resulted in a wide range of color morphs and patterns. Some Black Mollies’ scales have a metallic sheen, giving them a glossy appearance, while others have a matte finish. 

The size of Black Molly fish can vary depending on age, genetics, and environmental conditions. Adult Black Molly fish can average 3 to 4 inches (7.6 to 10.2 centimeters) long. There can be variations within the species, with some individuals growing slightly larger or smaller than the average size.


The Black Molly is a species that is easily sexually dimorphic, meaning there are distinct differences between males and females. Male Black Mollies are typically smaller and have longer, more flowing fins. The dorsal fin is especially prominent and is a distinguishing feature of the species. Female Black Mollies are typically larger and more robust in appearance. When female Black Mollies carry eggs, they may develop a gravid spot, a dark patch near their anal fin. 


The Black Molly are skilled swimmers known for their graceful, flowing movements. They are not afraid to explore their tank or interact with their tankmates. Black Mollies are known for their playful and social behavior when kept in a well-maintained tank with appropriate water conditions and a balanced diet. 


When choosing tankmates for your Black Molly, it is important to consider their peaceful temperament and active swimming behavior. Black Mollies are best kept with other peaceful species that will not harass or intimidate them. 

Some good tankmates for Black Mollies include:

Tank conditions

The Black Molly is a tough species that can adapt to various water conditions. They are frequently kept in freshwater tanks and can tolerate pH levels ranging from 7.0 to 8.0. The water temperature should be kept between 72 and 82°F, with 78°F being ideal. 

Regular water changes and a high-quality filtration system are essential for keeping your Black Mollies’ water clean and healthy. To maintain a stable, healthy environment for your fish, you should also provide plenty of swimming space, hiding places in your tank, and adequate aeration. 


Black Mollies have a simple diet as they are omnivores and eat plant- and animal-based foods. They eat various small insects, algae, and plant material in the wild. They can be fed a balanced diet of commercial flake or pellet food, as well as live or frozen foods like brine shrimp, bloodworms, and daphnia, in the aquarium. Black Mollies are known to be voracious eaters and consume as much food as possible, so it is important to monitor their food intake and adjust portions to avoid overfeeding.


Breeding Black Mollies is a simple process that can be rewarding for intermediate fish keepers. The first steps in the breeding process are selecting a healthy, mature pair of fish and providing suitable breeding conditions, such as a well-established aquarium with plenty of hiding places and live plants.

Black Mollies are livebearers, meaning they give birth to live young rather than laying eggs. The female will carry her young for approximately 4 to 6 weeks, after which she will give birth to anywhere from 10 to 60 fry. It is essential to provide suitable conditions for the fry, such as a separate breeding tank with plenty of hiding places and a balanced diet.


All fish species, including Black Mollies, are vulnerable to disease. Ich, Fin Rot, and Swim Bladder Disease are some of the most common diseases that affect Black Mollies.

Maintain good water quality in your Black Molly tank to help prevent disease spread. This includes regularly checking water parameters like pH, temperature, and ammonia levels and performing regular water changes.

Additionally, watch your Black Mollies for any signs of illness, such as color changes, loss of appetite, or abnormal swimming behavior. If you notice any signs of disease, you should quickly quarantine the affected fish, perform water changes, and seek veterinary advice if necessary.

To prevent disease spread, avoid overfeeding and overstocking your tank, as these conditions can contribute to poor water quality and increase the risk of disease.


Jason Matthews

My name is Jason Matthews, and welcome to my website. When other kids were bragging about how their dog could sit and roll over, I was bragging about my latest Betta Fish and the cool sea castle I just added to his aquarium. 

Jason aquariume

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