Black Molly

Black Mollies are enchanting freshwater fish that are easy to care for, making them a popular choice among aquarium enthusiasts. These friendly fish require minimal maintenance and are an excellent addition to community aquariums.

An icon to represent level of difficulty to care for a fish type.

Care DIfficulty


An icon to represent temperament.



An icon to represent origin.


Central and South America

An icon to represent size.


4 inches (10 cm)

An icon to represent a fish's lifespan.


5 years

List icon.

Table of contents

Origin, Appearance, Size, and Lifespan

The Black Molly, or Poecilia sphenops, is a beloved freshwater fish originating from Central and South America. They can be found in various environments, from fresh to brackish waters, in countries like Mexico, Guatemala, and Colombia.

In their natural habitats, Black Mollies are commonly found in slow-moving, densely vegetated waters. These plants serve as hiding spots and food sources, while the dark water helps their striking black coloration stand out. These social fish thrive in groups and are best kept in a community setting.

Their natural environment features warm water, with a temperature range of 72 to 82 degrees Fahrenheit (22 to 28 degrees Celsius). They prefer a pH level of 7.5 to 8.5 and water hardness between 10 to 25 dGH. To replicate a similar environment in your aquarium, maintain a consistent water temperature, use a high-quality filtration system, and incorporate live plants and decorations for hiding spots.

By closely mimicking the Black Molly's natural habitat and maintaining proper water conditions, you'll set your fish up for a healthy and content life in your aquarium.

Black Mollies are known for their stunning, velvety black color, which makes them a captivating addition to any aquarium. Although they are relatively small, growing up to around 4 inches (10 cm) in length, their striking appearance and lively nature make them an ideal choice for those seeking a visually appealing and active aquatic display. These delightful fish captivate observers as they gracefully swim through the tank, making them a treasured favorite among hobbyists of all experience levels.

With proper care, Black Mollies can live for up to five years. As social creatures, they thrive in groups and are best kept in community aquariums with compatible tank mates. To support their well-being and ensure a long life in captivity, it's crucial to provide a well-planted aquarium with plenty of hiding spots, as well as a varied diet consisting of high-quality flakes, pellets, and frozen foods.

Fun Facts

Now that we've learned more about the appearance and lifespan of Black Mollies, let's delve into some fascinating facts about these charming fish that make them stand out in the aquarium hobby. From their beautiful coloration to their adaptable nature, Black Mollies are full of surprises and are sure to enchant any aquarist.

  • Adaptable to various environments: In the wild, Black Mollies are found in diverse environments, from fresh to brackish waters. Their adaptability allows them to survive in various conditions, making them an appealing choice for aquarium hobbyists.
  • Natural algae eaters: Black Mollies have a unique appetite for algae, helping to keep your aquarium clean and algae-free. This natural algae-eating habit contributes to maintaining a balanced ecosystem in your tank.
  • Livebearers: Unlike many other fish species, Black Mollies are livebearers, which means they give birth to live young instead of laying eggs. This reproductive strategy helps ensure the survival of their offspring, as they are born fully formed and ready to swim.
  • Ability to change colors: Black Mollies can change the intensity of their color based on their surroundings, mood, or health. In dimly lit conditions or when stressed, their colors may appear less vibrant. Conversely, when they feel secure and healthy, their colors become more vivid, making them stand out in an aquarium setting.
  • Social behavior: Black Mollies are social fish, meaning they prefer to swim together with compatible tank mates. This behavior not only helps them feel secure but also creates an engaging visual display in an aquarium. Their lively movements and stunning black color can transform a home aquarium into a captivating underwater scene.

Now that you've discovered some intriguing tidbits about Black Mollies, you'll be better equipped to appreciate their beauty and unique characteristics in your aquarium. In the following section, we'll provide recommendations on tank setups, ensuring your Black Mollies have an ideal environment to flourish and showcase their alluring features.

Recommended Tank Setups

Each setup includes the core components—tank, filter, heater, lighting, substrate, and more—ensuring that you can create an appropriate environment for Black Mollies and other compatible freshwater fish species in your aquarium. As you move from budget-friendly to high-end setups, you will also have more options for customization, aesthetics, and advanced features. Black Mollies are social fish and need to be kept with suitable tank mates to ensure their well-being. Typically, Black Mollies are priced between $3 and $5 per fish, although prices can vary based on factors such as size, quality, and availability.

Budget-friendly setup (around $200):

  • Tank: 20-gallon aquarium with a hood or glass canopy ($40 - $70)
  • Filter: Hang-on-back (HOB) or sponge filter rated for 20 gallons ($20 - $40)
  • Heater: 50-100 watt adjustable aquarium heater ($15 - $30)
  • Lighting: Basic LED aquarium light ($20 - $50)
  • Substrate: Inexpensive aquarium sand or small gravel ($10 - $20)
  • Decor: A few pieces of driftwood and rocks, along with low-cost live plants like Java Fern and Anubias ($20 - $40)
  • Fish: 4-6 Black Mollies ($12 - $30)
  • Thermometer: $3 - $10
  • Substrate Vacuum: $10 - $25
  • Fish Net: $2 - $10
  • Algae Scraper or Magnetic Cleaner: $5 - $20
  • Siphon and Bucket: $15 - $30
  • Test Kit: $15 - $50
  • Fish Food: $5 - $20
  • Water Conditioner: $5 - $15

Mid-range setup (around $400 - $650):

  • Tank: 20-30 gallon aquarium with a hood or glass canopy ($60 - $120)
  • Filter: Canister filter or high-quality HOB filter rated for the tank size ($60 - $150)
  • Heater: 100-150 watt adjustable aquarium heater ($25 - $50)
  • Lighting: LED aquarium light with adjustable settings for plant growth and color enhancement ($50 - $150)
  • Substrate: Nutrient-rich aquarium substrate designed for planted tanks ($20 - $40)
  • Decor: A mix of driftwood, rocks, and live plants such as Amazon Swords, Java Fern, Anubias, and Cryptocoryne species ($40 - $80)
  • Fish: 4-8 Black Mollies ($12 - $40)
  • Thermometer: $3 - $10
  • Substrate Vacuum: $10 - $25
  • Fish Net: $2 - $10
  • Algae Scraper or Magnetic Cleaner: $5 - $20
  • Siphon and Bucket: $15 - $30
  • Test Kit: $15 - $50
  • Fish Food: $5 - $20
  • Water Conditioner: $5 - $15

High-end setup (above $800):

  • Tank: 30-40 gallon rimless aquarium with a glass canopy ($120 - $250)
  • Filter: High-quality canister filter rated for the tank size ($100 - $250)
  • Heater: 150-200 watt adjustable aquarium heater with an external temperature controller ($40 - $80)
  • Lighting: Advanced LED lighting system with customizable settings for plant growth, color enhancement, and day/night cycles ($150 - $300)
  • Substrate: Premium aquarium substrate designed for planted tanks, with added root tabs for extra plant nutrition ($30 - $60)
  • Decor: A combination of driftwood, rocks, and live plants to create a natural aquascape, featuring plant species such as Amazon Swords, Java Fern, Anubias, Cryptocoryne species, and carpeting plants like Dwarf Hairgrass or Monte Carlo ($60 - $150)
  • Fish: 4-12 Black Mollies ($12 - $60)
  • Thermometer: $3 - $10
  • Substrate Vacuum: $10 - $25
  • Fish Net: $2 - $10
  • Algae Scraper or Magnetic Cleaner: $5 - $20
  • Siphon and Bucket: $15 - $30
  • Test Kit: $15 - $50
  • Fish Food: $5 - $20
  • Water Conditioner: $5 - $15

Please note that these numbers are just recommendations, and you should consider other factors such as tank mates and individual fish personalities when deciding how many Black Mollies to keep in your aquarium. Prices may vary depending on location, brand, and availability.

Set Up Your Tank

In the previous section, we discussed the recommended tank setups for your Black Mollies and other fish. Now that you have a better understanding of what's required, let's dive into the step-by-step process of setting up your aquarium. These steps will guide you through selecting the ideal location for your tank, cleaning and preparing the tank, installing essential equipment, and cycling the water to create a healthy environment for your fish. We'll also cover the proper acclimation process to ensure a smooth transition for your Black Mollies and other fish into their new home. By following these guidelines, you'll be well on your way to creating a thriving aquatic ecosystem for your fish to flourish in.

  • Step #1: Choose the perfect spot for your aquarium, making sure it's away from direct sunlight, heat sources, and drafts. Ensure the surface is level and sturdy enough to support your filled tank. If your aquarium requires a stand, assemble it according to the manufacturer's instructions and place the empty tank on it.
  • Step #2: Next, clean the tank by rinsing it with clean water (avoid using soap or chemicals) to remove dust or debris. Wipe the inside with a clean cloth or paper towel. Rinse the substrate (sand or gravel) thoroughly in a bucket until the water runs clear, then spread it evenly across the bottom of the tank, creating a slight slope towards the back for visual depth.
  • Step #3: Before filling the tank with water, plan the layout of your aquarium, including the position of equipment like heaters and filters. This will make it easier to set up and maintain the tank in the long run. Install the heater and filter according to the manufacturer's instructions. If you're using a sponge or under-gravel filter, place it beneath the substrate before adding water.
  • Step #4: Decorate the tank with driftwood, rocks, and plants to create hiding spots and a visually appealing environment, ensuring there are open swimming areas for your fish. When decorating the tank, be careful to arrange driftwood, rocks, and plants in a way that won't damage or obstruct the equipment. You can also anchor plants to driftwood or rocks to help them stay in place.
  • Step #5: Fill the tank with water treated with a water conditioner if your tap water contains chlorine or chloramines. Place a clean plate or plastic bag on the substrate to prevent disturbance while filling. Fill the tank until it's about 2/3 full. Attach the aquarium light to the hood or canopy, following the manufacturer's instructions. Consider using a timer for your aquarium light to maintain a consistent day and night cycle, which is essential for fish and plants. Connect the heater, filter, and any additional equipment (air pump, CO2 system) to power sources, and install the thermometer in an easily visible location.
  • Step #6: Top off the water, leaving space between the water surface and the top of the tank for oxygen exchange. Turn on the filter, heater, and other equipment. Monitor the water temperature and adjust the heater as needed. Allow the tank to cycle for 4-6 weeks to establish beneficial bacteria and stabilize water parameters. During the cycling process, you can add a bacterial starter culture to speed up the establishment of beneficial bacteria in the tank. Use an aquarium test kit to monitor ammonia, nitrite, and nitrate levels.
  • Step #7: After the tank has cycled and water parameters are stable, slowly acclimate your Black Mollies to the tank's conditions before introducing them. Begin by floating the unopened fish bag in the tank for 15-20 minutes to equalize the temperature. Afterward, open the bag and add a small amount of tank water to it. Continue adding small amounts of tank water to the bag every 5-10 minutes for at least 30-60 minutes, allowing the fish to adjust to the new water chemistry gradually. Use a net to gently transfer the fish from the bag to the tank, avoiding any unnecessary stress or exposure to the water from the bag.
  • Step #8: Once all the fish are introduced, establish a consistent daily feeding schedule, providing high-quality food in appropriate amounts for your Black Mollies. Perform regular water changes (20-30% every 1-2 weeks) and monitor water parameters using a test kit to maintain a healthy environment for your fish. Observe your Black Mollies closely for any signs of stress or illness, especially during the first few weeks after introduction. Be prepared to take action if necessary, such as adjusting water parameters or seeking advice from an experienced aquarist.

By following this step-by-step guide and incorporating the additional setup tips, you can create a thriving aquatic environment that will help your Black Mollies flourish in their new home.

Recommended Water Parameters

To ensure the health and well-being of your Black Mollies, it is important to maintain specific water parameters in your aquarium. Here's a breakdown of the ideal conditions to aim for:

  • Temperature: Keep the water temperature between 75°F and 82°F (24°C and 28°C) to provide optimal comfort for your Black Mollies.
  • pH: Aim for a slightly alkaline pH level ranging from 7.5 to 8.5, as Black Mollies prefer slightly harder water.
  • Hardness: Maintain moderately hard water with a hardness level of 10 to 20 dGH.
  • Ammonia, Nitrite, and Nitrate: Keep ammonia and nitrite levels at 0 ppm, and maintain nitrate levels below 40 ppm.
  • Lighting: Provide moderate lighting with shaded areas and plants to create a natural habitat for your Black Mollies.
  • Water movement: Ensure moderate water flow in the tank, mimicking their natural environment.

Make sure to test your aquarium water regularly and perform necessary water changes to keep the environment stable.

Routine Water Maintenance

Regular water maintenance is crucial for a healthy Black Molly tank. Follow these guidelines to keep your aquarium in optimal condition:

  • Weekly water changes: Replace 20-25% of the tank water every week to remove accumulated waste and maintain water quality.
  • Test water parameters: Regularly test the pH, ammonia, nitrite, nitrate, and hardness levels to ensure they are within the recommended ranges.
  • Use a gravel vacuum: During water changes, use a gravel vacuum to clean the substrate and remove any debris or uneaten food.
  • Dechlorinate the water: Treat tap water with a water conditioner to remove chlorine and chloramines before adding it to the aquarium.
  • Match temperature and pH: Ensure that the new water added during water changes has a temperature and pH level similar to the existing tank water.
  • Acclimate the fish: After water changes, allow your Black Mollies to adjust to the new conditions by gradually introducing them to the fresh water.

In addition to routine water maintenance, consider the following tips to ensure the health of your fish and the overall appearance of your aquarium:

  • Monitor lighting duration: Keep track of the duration of your aquarium lights, aiming for a consistent 8-10 hour photoperiod each day. Too much light can lead to excessive algae growth.
  • Plant maintenance: Regularly trim and prune live plants to maintain their health and appearance. Remove any dead leaves or decaying plant matter to prevent water quality issues.
  • Filter maintenance: Clean or replace the filter media as recommended by the manufacturer to ensure efficient filtration. Avoid replacing all filter media at once to preserve the beneficial bacteria population.

Diet and Feeding Schedule

Black Mollies are omnivorous and require a varied diet to thrive. Here are some feeding guidelines to keep in mind:

  • Flakes and pellets: Offer high-quality flake or pellet food designed for tropical fish as the staple diet for your Black Mollies.
  • Frozen and live foods: Provide occasional treats of brine shrimp, bloodworms, daphnia, or mosquito larvae to offer a diverse range of nutrients.
  • Vegetable matter: Supplement their diet with blanched spinach, zucchini, or cucumber to provide essential vitamins and fiber.
  • Feeding frequency: Feed your Black Mollies small portions two to three times a day to prevent overfeeding and maintain water quality.

Ensure that any uneaten food is promptly removed from the tank to prevent water contamination.

Stress and Diseases

Black Mollies may experience stress due to various factors. Here are some tips to minimize stress and prevent diseases in your Black Mollies:

  1. Watch for stress signs: Keep an eye out for unusual behavior such as hiding, loss of appetite, rapid breathing, or color fading, as these may indicate stress. Address any potential stressors promptly.
  2. Check water quality: Regularly test the water parameters to ensure they are within the recommended ranges. Maintain excellent water quality by performing regular water changes and proper filtration.
  3. Monitor tank mates: Ensure that your Black Mollies are not being harassed or bullied by other fish in the tank. If necessary, separate aggressive tank mates or provide hiding places to reduce stress.
  4. Create a suitable habitat: Provide plenty of hiding spots, live plants, and appropriate tank decorations to mimic their natural habitat. This helps reduce stress and provides a sense of security for your Black Mollies.

While Black Mollies are generally hardy, they can be susceptible to common fish diseases. Here are a few to be aware of:

  • Ich (white spot disease): A parasitic infection characterized by white spots on the fish's body and fins. Treat ich with appropriate medication and raise the water temperature gradually to help eradicate the parasites.
  • Fin rot: A bacterial infection that causes frayed or discolored fins and tail. Treat fin rot by maintaining excellent water quality, using appropriate antibacterial medication, and removing any affected fish from the main tank.
  • Velvet disease: A parasitic infection that appears as a yellowish or gold dust-like coating on the fish's body. Treat velvet disease with suitable medication containing copper sulfate or malachite green.
  • Swim bladder disease: A condition where fish have difficulty maintaining their balance and swim erratically. Adjust the diet to include easily digestible foods and ensure proper water conditions.

To prevent diseases, maintain a clean and well-maintained aquarium, provide a balanced diet, and avoid introducing sick fish into the tank. Quarantine new fish before adding them to the main tank to minimize the risk of introducing diseases.


Breeding Black Mollies can be an exciting endeavor. While they are known for their prolific breeding habits, creating the right conditions is essential. Here's a general guide to breeding Black Mollies:

  1. Setting up a breeding tank: Prepare a separate breeding tank with appropriate water parameters, including a temperature of around 78°F (25°C) and slightly alkaline water with a pH of 7.5 to 8.5. Provide plants or spawning mops as hiding places for the fry.
  2. Selecting breeding pairs: Choose healthy and mature male and female Black Mollies for breeding. Maintain a ratio of two females to one male to prevent excessive harassment.
  3. Conditioning the breeders: Feed the breeding pair a varied and nutritious diet, including live or frozen foods, to ensure they are in optimal breeding condition.
  4. Introducing the breeders: Place the male and females together in the breeding tank and monitor their behavior. The female Black Molly will give birth to live fry, so you don't need a separate spawning site.
  5. Providing fry protection: Once the fry are born, remove the adults from the breeding tank to prevent them from consuming the fry. Provide ample hiding places and fine-leaved plants to protect the fry and increase their survival rate.
  6. Feeding the fry: Feed the fry small, finely crushed flakes or specialized fry food to ensure their proper growth and development. Perform regular water changes to maintain good water quality.

Remember, breeding Black Mollies can be a rewarding experience, but it requires careful attention to water conditions, proper nutrition, and fry protection.

Recommended Tank Mates

Here are the top 10 recommended tank mates for Black Mollies:

  1. Dwarf Corydoras
  2. Neon Tetras
  3. Ember Tetras
  4. Guppies
  5. Bristlenose Plecos
  6. Pygmy Corydoras
  7. Cherry Shrimp
  8. Nerite Snails
  9. Rasboras
  10. Otocinclus Catfish

Remember to avoid large, aggressive fish like cichlids, angelfish, and predatory species, as they may harm or eat the Black Mollies. Always observe the behavior of new fish and ensure they don't cause stress or aggression towards the Black Mollies.


To summarize, Black Mollies are captivating freshwater fish known for their vibrant colors and ease of care. They require specific water parameters, a balanced diet, and a suitable environment to thrive in captivity. Choosing peaceful tank mates and providing ideal conditions will ensure a harmonious community. Breeding Black Mollies can be challenging but rewarding with patience and the right setup. Overall, Black Mollies are stunning and lively fish that can enhance any aquarium with their vibrant hues and active behavior.

Frequently Asked Questions

What is the ideal tank size for Black Mollies?

When housing Black Mollies, a 20-gallon tank is the minimum recommended size for a small group. A larger tank is even better, as it provides stability in water conditions and ample swimming space for the fish.

How many Black Mollies should be kept together?

Black Mollies are schooling fish, so it's best to keep them in groups of at least 6-8 individuals. Maintaining a larger group helps the fish feel safer and encourages natural behavior.

What water parameters do Black Mollies require?

Black Mollies thrive in water temperatures between 75°F and 82°F (24°C and 28°C), a pH between 7.5 and 8.5, and moderately hard water with a hardness level between 10 and 20 dGH.

What do Black Mollies eat?

Black Mollies are omnivorous and require a varied diet. Feed them a mix of high-quality flake or pellet food, along with live or frozen foods such as daphnia, brine shrimp, and bloodworms.

Are Black Mollies compatible with other fish?

Yes, Black Mollies are generally peaceful and can coexist with other similarly sized, non-aggressive fish species. Suitable tank mates include other small tetras, rasboras, corydoras catfish, and small plecos.

How can I differentiate between Black Mollies and other fish species?

Black Mollies have a distinct black coloration, and the males often have a sail-like dorsal fin. Pay attention to these physical characteristics to identify them accurately.

How long do Black Mollies live?

With proper care and optimal tank conditions, Black Mollies can live for 3 to 5 years.

How do I breed Black Mollies?

Breeding Black Mollies can be achieved by providing specific water conditions, such as slightly brackish water and a separate breeding tank. Separate males and females and introduce them for spawning.

Do Black Mollies require a planted tank?

While not strictly necessary, a planted tank is highly recommended for Black Mollies. Live plants provide hiding spots, improve water quality, and create a natural environment similar to their native habitat.

Can Black Mollies change color?

Yes, Black Mollies can exhibit color changes due to various factors such as stress, illness, or changes in water conditions. If you notice your Black Mollies experiencing a loss of color, it's important to assess the water parameters and monitor their overall health.