How Big Do Black Molly Fish Get: (The Ultimate Guide)

Black molly fish are popular for many aquarium enthusiasts, thanks to their striking appearance and relatively easy care requirements. However, one of the most common questions that potential black molly owners have is, “How big do black molly fish get?”

In this ultimate guide, we will delve into the world of black molly fish to explore their growth potential and provide insights into how to ensure they thrive in your aquarium.

As we explore this topic, we will cover various aspects of black molly fish, including their natural habitat, dietary needs, and ideal tank conditions.

are black mollies aggressive

Understanding the growth potential of black mollyfish is crucial for providing them with the proper care, and our guide aims to equip you with all the necessary information to do just that.

Whether you are a beginner or an experienced aquarium hobbyist, this comprehensive guide will provide valuable insights into the growth and care of black molly fish.

By the end of this article, you will clearly understand how big these fish can get and how to ensure they lead healthy, happy lives in your aquarium. 

How Big Do Black Molly Fish Get in Aquarium?

Black Molly fish can grow to be around 3 to 5 inches long when kept in an aquarium. However, their size can vary based on various factors such as the quality of their care, diet, and genetics.

Providing this shoaling fish with a spacious tank for plenty of swimming space is essential. A minimum tank size of 10 gallons is recommended for a small group of Black Molly fish.

Keeping the water clean and well-maintained is crucial for their growth and overall health.

black molly fish

Good water quality will also help to prevent stunted growth, which can occur if the fish are kept in inadequate conditions.

Providing a balanced diet that includes a variety of foods such as flakes, pellets, and live or frozen foods will also contribute to their growth potential.

With proper care, Black Molly fish can reach their full size potential and live a healthy and active life in the aquarium. 

Molly Fish Size & Growth Chart

Molly fish, also known as the Poecilia sphenops, can grow around 2 to 5 inches in length. The growth rate of Molly fish can vary depending on various factors such as water quality, diet, and tank size.

In terms of the difference between male and female black molly size, male Molly fish tend to be smaller than female molly fish, with the males reaching around 2 inches and the female mollies growing up to 4 inches in length.

Molly fish’s growth chart usually shows a steady increase in size within the first few months of their lives. Proper care and maintenance of the tank environment, along with a balanced diet, can contribute to the healthy growth of Molly fish.

It’s important to note that overcrowding in the tank can stunt the growth of Molly fish, so it’s recommended to provide them with ample room to grow and thrive.

Following a growth chart and providing the right conditions, Molly fish can reach their full potential and live a healthy life in a well-maintained aquarium. 

Here’s a comprehensive overview of Molly fish size and growth, including a chart for reference:

General Information:

  • Average Adult Mollies Size: 2-4 inches (5-10cm)
  • Maximum Adult Size: 6 inches (15cm)
  • Growth Rate: Moderate
  • Sexual Maturity: 3-4 months

Growth Chart:

AgeAverage LengthRange
Birth0.25 inches (0.6cm)0.2-0.3 inches (0.5-0.7cm)
1 week0.5 inches (1.2cm)0.4-0.6 inches (1-1.5cm)
2 weeks0.75 inches (1.9cm)0.6-0.9 inches (1.5-2.3cm)
1 month1 inch (2.5cm)0.8-1.2 inches (2-3cm)
2 months1.5 inches (3.8cm)1.2-1.8 inches (3-4.5cm)
3 months2 inches (5cm)1.8-2.5 inches (4.5-6.3cm)
4 months2.5 inches (6.3cm)2.2-3 inches (5.5-7.6cm)
6 months3 inches (7.6cm)2.5-3.5 inches (6.3-8.9cm)
1 year3.5 inches (8.9cm)3-4 inches (7.6-10cm)
2+ years4+ inches (10+cm)3.5-6 inches (8.9-15cm)

Factors Affecting Growth:

  • Genetics: Some molly breeds naturally grow larger than others.
  • Diet: A healthy diet rich in protein and nutrients will promote faster growth.
  • Water Quality: Clean, well-maintained water is essential for optimal health and development.
  • Tank Size: A larger tank will provide more space for mollies to grow and thrive.
  • Competition: Overcrowding can limit the growth of molly fish.

Additional notes:

  • This chart is an estimate, and actual growth rates may vary.
  • Mollies can continue to grow slowly after reaching their adult size.
  • Females tend to be slightly larger than males.

What Should I Know About Molly Fish Care Before I Purchase Mollies?

Before purchasing Mollies, there are several factors to consider about their care. Mollies are tropical fish requiring a warm and stable water temperature. It is essential to have a heater in their aquarium to maintain a temperature between 75-80°F.

Mollies also prefer a well-established tank with many plants and hiding spots, as they are active swimmers and like to explore their surroundings. It is essential to feed them a varied diet, including high-quality flake or pellet food and occasional treats such as frozen or live foods.

Additionally, Mollies are peaceful fish and should be kept in a community tank with other temperate species that can tolerate the same water conditions. It is crucial to regularly monitor the water parameters and maintain a clean tank environment to ensure the health and well-being of Mollies.

Proper Molly fish care involves maintaining a suitable habitat, providing a balanced diet, and ensuring compatibility with other tankmates. 

Common Types Of Mollies

Here are some of the most common molly types found in the aquarium hobby:

By species:

Shortfin Molly (Poecilia sphenops): 

  • The most common type of Molly in the aquarium hobby.
  • It is relatively small, reaching a maximum length of about 4 inches.
  • Available in various colors, including black, gold, white, and Dalmatian (white with black spots).
  • They are Hardy and easy to care for, making them a good choice for beginners.

Sailfin Molly (Poecilia latipinna): 

  • Larger than the short-finned Molly, it reaches up to 6 inches in length.
  • The most distinctive feature is the large, sail-like dorsal fin.
  • Available in a variety of colors, similar to the shortfin Molly.
  • Generally, it is more peaceful than the shortfin Molly but can be more aggressive towards other fish.

Lyretail Molly (Poecilia velifera):

  • A cross between the short finned and sailfin Molly.
  • Has a large, fan-shaped tail and anal fin.
  • Available in various colors, similar to the shortfin and sailfin molly.
  • Generally peaceful and easy to care for.

Balloon Molly:

  • A variety of both the shortfin and sailfin molly.
  • Has a rounded, balloon-shaped body.
  • They can be more challenging to care for than other types of molly fish due to their body shape.
  • Available in various colors, similar to the shortfin and sailfin molly.

Dalmatian Molly:

  • A variety of both the shortfin and sailfin molly.
  • Has black spots on a white body.
  • Available in various colors, similar to the shortfin and sailfin molly.
  • Generally peaceful and easy to care for.

Other common types of Mollies:

Black Molly:

  • A solid black variety of the shortfin Molly.
  • Hardy and easy to care for.

Gold Dust Molly:

  • A variety of the shortfin Molly with gold dust-like markings on its body.
  • Hardy and easy to care for.

Platinum Molly:

  • A variety of the shortfin Molly with a shimmering platinum color.
  • Hardy and easy to care for.

Red Sunset Molly:

  • A variety of the shortfin Molly with a red and orange body.
  • Hardy and easy to care for.

Chocolate Molly:

  • A variety of the shortfin Molly with a chocolate brown body.
  • Hardy and easy to care for.

This is not an exhaustive list, but it includes some of the most popular types of mollies in fish stores. When choosing mollies for your aquarium, it is crucial to consider the size of your tank, the other fish you have, and your personal preferences.

black molly fish price

The price of black molly fish can vary depending on a few factors. Generally, a black molly fish can range from $3 to $5 per fish. However, the price may fluctuate based on the size and coloration of the fish, as well as the breeder or seller.

More considerable, more vibrant black molly fish may be priced higher than smaller, less colorful ones. The location and availability of black molly fish can also influence the price, with some regions or stores selling them for slightly different prices.

It’s also worth noting that specialty or rare color morphs of black molly fish may be priced higher due to their unique and sought-after appearances. Black molly fish are generally affordable and accessible for aquarium hobbyists, making them a popular choice for beginner and experienced fish keepers.

What Is the Usual Molly Fish Lifespan?

The usual lifespan of a molly fish is 2 to 5 years. However, several factors can influence their lifespan, with proper care potentially extending their life expectancy.

Here’s a breakdown of the lifespan based on different circumstances:


  • Average: 3-5 years
  • Optimal care: 5-7 years
  • Poor care: 1-2 years


  • Average: 1 year (after reaching sexual maturity)

Here are some tips to promote a longer lifespan for your molly fish:

  • Maintain a clean and spacious tank: This provides a healthy environment and reduces stress.
  • Monitor water parameters: Ensure the water temperature, pH, and ammonia levels are within optimal range for mollies.
  • Provide a balanced diet: Feed them high-quality flakes, pellets, and live or frozen food.
  • Keep compatible tank mates: Avoid aggressive fish that could stress or injure your mollies.
  • Maintain good water quality: Perform regular water changes and filter maintenance.
  • Minimize stress: Avoid overcrowding the tank and introduce new fish gradually.

Following these tips can create a favorable environment and help your molly fish live a long and healthy life.

Perfect Tank Conditions For Black Molly Fish

Black Molly fish thrive in aquariums with clean, well-maintained water and a temperature range between 75-80°F (24-27°C). The ideal pH level for their tank is between 7.5 and 8.5, and they prefer water with high alkalinity and hardness.

It is essential to provide plenty of hiding spots and floating plants for the Black Molly fish to feel secure and simulate their natural habitat. A tank size of at least 20 gallons is recommended to accommodate their active nature and ensure they have enough space to swim around.

Regular water changes and proper filtration are essential for maintaining optimal tank conditions for Black Molly fish, as they are sensitive to poor water quality.

By ensuring their separate tank meets these conditions, Black molly fish are more likely to display their vibrant colors and playful behavior, creating a visually appealing and engaging addition to any aquarium. 

Molly Fish Food & Diet: (Feeding Black Molly Fish)

Black Mollies are omnivores, meaning they eat a mix of animal and plant matter foods. In the wild, they graze on algae, biofilm, and small invertebrates. In an aquarium, you can replicate their natural diet by providing a variety of high-quality foods.

Here’s what you need to know about feeding your Black Mollies:


  • High-quality flakes or pellets: These should be the staple of your Molly’s diet. Look for flakes or pellets that are specifically formulated for omnivorous fish.
  • Frozen foods: Frozen bloodworms, brine shrimp, and daphnia are excellent protein sources and vital nutrients for Mollies. Offer these as treats a few times a week.
  • Algae wafers: These provide Mollies with the fiber they need for healthy digestion. Choose wafers made with spirulina, a type of algae high in vitamins and minerals.
  • Blanched vegetables: Spinach, lettuce, and peas can be a good source of vitamins and minerals for Mollies. Be sure to blanch the vegetables before feeding them to your fish, as this will make them easier to digest.
  • Live plants: Mollies will enjoy grazing on live plants in your aquarium. This provides them with a constant food source and helps keep the water clean. Good choices for Mollies include Java moss, water wisteria, and hornwort.

Feeding tips:

  • Feed your Mollies 2-3 times a day. Offer only as much food as they can eat in 2-3 minutes.
  • Remove any uneaten food after 5 minutes to prevent the water from becoming polluted.
  • Vary your Molly’s diet to ensure they get all the necessary nutrients.
  • Don’t overfeed your Mollies, as this can lead to obesity and health problems.

Black Molly Suitable Tank Mates

Black Molly fish are social creatures and can thrive in a community tank with other fish species. Suitable tank mates for Black Molly fish include peaceful community fish such as guppies, neon tetras, and platies. These fish are not aggressive and can coexist peacefully with the Black Molly.

Additionally, bottom-dwelling fish like Corydoras and Otocinclus catfish also make good tank mates for Black Molly, as they usually inhabit the lower region of the tank, leaving the middle and top areas for the Molly fish to roam.

It is essential to ensure that the tank mates are not too tiny or aggressive, as they may get bullied or even eaten by the Black Molly. Choosing peaceful and similarly sized fish as tank mates for Black Molly fish is crucial for creating a harmonious and thriving community tank.

Black Molly Care & Molly Tank Setup

Black mollies are a popular and easy-to-care-for freshwater fish, making them an excellent choice for beginner aquarists.

When setting up a tank for black mollies, it’s essential to ensure the water is consistently warm (around 75-80°F) and slightly alkaline, with a pH of 7.5-8.5.

A well-planted tank with plenty of hiding spots and open swimming areas is ideal. Black mollies are omnivores, so their diet should consist of a variety of foods, including high-quality flake or pellet food and occasional treats of live or frozen foods.

Regular water changes and proper filtration are also necessary to maintain a healthy tank environment for black mollies. Additionally, be mindful of tank mates, as black mollies can be prone to fin nipping from aggressive fish. By providing the proper care and tank setup, black mollies can thrive and bring beauty to your aquarium.

How many black mollies should be kept together?

Black mollies thrive in groups of 6 or more! This provides them comfort and security, similar to how they live in the wild.

What size tank does a molly need?

A 20-gallon tank is the minimum size for a single molly. However, a 29-55 gallon tank is recommended for larger mollies or multiple fish, ensuring ample swimming space and optimal health.

What do black mollies eat?

Black mollies are omnivorous, enjoying a diet of flakes, pellets, algae wafers, and live or frozen brine shrimp and bloodworms. Offer a varied diet for optimal health!

Can I keep a single molly?

While technically possible, a single molly isn’t ideal. They are social fish and thrive in groups of 6+ for comfort and reduced stress. Consider introducing more mollies for a happier fish!

Can Molly fish live in a 10-gallon tank?

A 10-gallon tank is too small for most mollies long-term. They reach 3-6 inches and need 20+ gallons for optimal health and swimming space. Consider a larger tank for happy mollies!

How many black mollies should I get?

Start with 3 black mollies for a 10-gallon tank. Add more as your tank size allows, but avoid overcrowding. Remember, happy mollies are social mollies!

How do you keep black mollies alive?

Keep your black mollies thriving with a stable 78°F tank, proper filtration, regular water changes, and a varied diet of flakes, pellets, and live or frozen foods.

Why is my Black Molly so aggressive?

Several factors could contribute to your Black Molly’s aggression: overcrowding, competition for food or mates, territoriality, or illness. Assess your fish tank setup, observe other fish interactions, and consider isolating the Molly if necessary. Consult a veterinarian for medical advice.

Are black Molly fish aggressive?

Black mollies are generally peaceful fish, but some individuals can become aggressive due to overcrowding, lack of hiding places, or competition for food or mates.

What is the lifespan of a black molly fish?

Black mollies can live for 3-5 years with proper care, including a stable tank environment, good water quality, and a healthy diet.

How long are black Molly fish pregnant?

Black mollies have a gestation period of 4-6 weeks, depending on water temperature and the individual fish. Keep the mother well-fed and offer plenty of hiding places for molly fry.

Is Breeding Black Molly fish easy?

Yes! Black mollies are prolific breeders, readily reproducing in a stable breeding tank. However, providing adequate baby fish care, including separate fry tanks and proper feeding, is crucial.

Can you put Molly with betta fish?

No, it’s not recommended. Mollies are too active and colorful, stressing and potentially harming your betta. Consider fish like neon tetras or Harlequin Rasboras as safer tankmates.

Where do Black Molly fish come from?

Despite their name, Black Mollies originated in the southern United States, not Africa. They were selectively bred from wild Sailfin Mollies in the 1920s.

Can black mollies live in brackish water?

Black mollies can tolerate slightly brackish water, but they prefer freshwater aquariums. They thrive in a stable environment with a pH between 7.0-7.8 and water hardness of 15-30 dGH.


So, how big can a black molly fish get? In conclusion, we’ve explored the fascinating world of black molly fish and discovered just how captivating these aquatic creatures can be. From their striking appearance to their playful personalities, black molly fish has captured the hearts of many hobbyists and aquarium enthusiasts. As we’ve seen throughout this blog post, black molly fish can grow to various sizes depending on their environment and genetics.

So, how big do black mollies get in aquariums? If you’re considering adding these delightful fish to your aquarium, providing them with adequate space and care is essential. Understanding How big do Black Molly fish get is crucial for their well-being and overall happiness. Happy fish keeping!

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About Me

I am the founder of, a devoted wife and mother, and an avid fish enthusiast. My aim is to assist fellow fish lovers worldwide in understanding how to properly care for and breed their pet fish.

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