- Family: Poeciliidae
- Scientific Name: Poecilia spp.
- Care level: Easy
- Temperament: Peaceful
- Diet: Omnivorous
- Water conditions: Freshwater, 25 – 28 degrees Celsius (72 – 82F), 6.5 – 8 pH
- Max Size: 10 centimeters (4 inches)
- Minimum tank size (as an adult): 40 Liters (10 gallons)
Brief Overview: Molly Fish Care
Mollies are a small tropical fish originating from freshwater streams of South, Central, and North America. A coastal fish, they have been known to inhabit brackish water, swamps, and are even occasionally found in the ocean. This ability to tolerate both fresh and saltwater makes Mollies a unique fish.
Molly Fish have a flattened body, tall in the middle and narrowing to a point at the mouth. Their caudal fin is large, fan-shaped, and can be either transparent or colorful. The dorsal fin can be a similar fan-shape or flatter against the body, depending on the type.
Molly fish are livebearers, breeding prolifically to “give birth” to offspring; they do not lay eggs like many other fish species. Males and females are easy to differentiate as females have a fan-shaped anal fin and males traditionally have a pointier anal fin. In a mixed-sex tank, females are almost always pregnant, which also makes them easier to identify.
Mollies are one of the most common fish in the aquarium hobby, popular for their gentle nature and attractive coloration. These easy-keepers make an excellent choice for an inexperienced or even brand new aquarist.
Molly Fish Lifespan
How Long Do Molly Fish Live For?
Mollies have a life expectancy of about 3 to 5 years in an aquarium with excellent care and conditions. Balloon Mollies, individuals who have been selected and bred with a spinal disfigurement that gives them a balloon shape, experience a shorter lifespan.
How fast/slow should you expect your Molly Fish to grow?
Mollies mature quickly, reaching sexual maturity around 3 to 4 months of age.
What are Molly Fish max size?
The maximum size of a Short-finned Molly is 10 centimeters (4 inches). The Sailfin Molly and Mexican Sailfin Molly grow slightly larger, reaching up to 15 centimeters (6 inches) in length.
Different types of Molly Fish
Often mistaken as one species, there are actually three species of Molly available in most fish stores, but extensive hybridization and breeding in captivity between the three have made them almost impossible to differentiate. Wild-caught mollies offered for sale are most likely either Sailfin Mollies (Poecilia latipinna) or Short Finned Mollies (Poecilia sphenops).
Sailfin Mollies are the most common type of Molly, found in coastal areas of the southeast United States and the Gulf of Mexico. They are prolific breeders and have a high tolerance for salt water.
Short-finned Mollies adapt to aquarium life better than any other Molly, making them one of the best choices available for a beginner fish keeper. Like the Sailfin Molly, this species can tolerate high salinity and breeds readily.
The third species of Molly found in aquariums is the Mexican Sailfin Molly (Poecilia velifera). Found in the coastal areas of the Yucatan, this species can also tolerate salt water. Mexican Sailfin Mollies are difficult to keep in aquariums and do not breed as readily as other Mollies, and as a result, are much rarer to find in captivity.
These species of Molly have been hybridized to produce a vast variety of color morphs. Here are some of the most popular Molly variations among fishkeepers:
Dalmatian Molly: Named for their black and white spots similar to the popular dog breed, Dalmation Mollies are also known as the Marbled Molly or Marbled Sailfin Molly.
Black Molly: Black Mollies are completely black in coloration and otherwise very similar to the Short-Finned Molly. Some Black Mollies have gold or silver patches when they are young but these fade as they age.
Lyretail Molly: This fish is named for its large, pointed tail. They are also called the Giant Lyretail Molly, Mexican Lyretail Molly, and Yucatan Molly. Variations can be seen with platinum, green, and gold-colored scales.
Sailfin Molly: Sailfin Mollies are aptly named for their sail-like dorsal fin and can have scales of almost any color including bright orange, metallic green, yellow/orange, and white.
Balloon Molly: This type of Molly is produced by selectively breeding for a spine mutation that gives Mollies an arched back and rounded belly, resembling a balloon. These fish experience shorter life expectancies and trouble swimming. Balloon Mollies can exhibit a variety of coloration.
Gold Molly: A short-finned Molly bred for eye-catching bright metallic orange scales.
Black Mottled Molly: This beautiful variant is commonly seen as a Lyretail and exhibits a gold and white scale coloration with black spots across its body.
Molly Fish Diet & Feeding
Mollies are omnivorous and can eat just about anything. Variety in the diet of your Molly is important to ensure they receive well-balanced nutrition.
What do Molly Fish eat in the wild?
Mollies are native to creeks and streams of North, Central, and South America. In the wild, they feed on a combination of aquatic plants, algae, and small invertebrates.
What foods are recommended for Molly Fish?
In an aquarium setting, Mollies can be fed a combination of fresh, frozen, and flake foods. You should plan to feed your Molly a high-quality flake food supplemented with vegetables and the occasional protein treat. Vegetables such as zucchini, cucumber, spirulina, and peas are all excellent choices for Mollies. For the occasional protein, consider live or frozen bloodworms, brine shrimp, daphnia, blackworms, or bloodworms.
Molly Fish Feeding habits
Feed your Mollies two to three times a day but avoid overfeeding; never offer more food than your fish can consume in 2 to 3 minutes. Mollies are especially known for overeating and may also feed on live plants in their tank. Uneaten food in your tank can also affect water quality, causing nitrogen levels to spike.
Gourami Fish Tank Setup
Like all fish, Mollies thrive best in a tank that resembles their natural habitat and suits their needs.
A brief overview of natural habitat
Mollies generally inhabit areas of slow-moving creeks and streams in coastal regions of North, Central, and South America. They prefer heavily vegetated environments but have also been found to thrive in brackish and even ocean waters.
Molly Fish Tank Size
Tank size requirements for Mollies are relatively minimal. The smallest species, the Short-Finned Molly, can adjust well in a tank as small as 40 liters (10 gallons). Larger varieties may need a bigger tank, but even the largest variety will do well in a 115-liter (30-gallon) tank. Larger tanks offer more stable environments, are less prone to sudden changes, and are an overall better choice for your Mollies.
Molly Fish Water Conditions
Species of Molly are incredibly hardy, able to live in both freshwater and saltwater environments. They prefer freshwater between 25 and 28 degrees Celsius (72 to 82 degrees Fahrenheit) and a pH between 6.5 and 8. Mollies are not necessarily messy eaters, but some of the hybrid varieties can be more susceptible to diseases, so a well-filtrated tank is ideal. Some aquarists add a small amount of salt to their tank.
Mollies prefer a sandy substrate along the bottom of their tanks. Though Mollies don’t spend much time near the bottom of their aquarium, the sandy substrate is suitable for the live plants Mollies favor. Choose tall plant options like Anubias to offer shelter for your Mollies, but also be aware they may feed on any live plants in their tank.
Offer your Mollies decorations that create caves and crevices so this peaceful fish has places to escape possible harassment.
Molly Fish Tank Mates
Mollies are generally peaceful and social by nature. Males can be aggressive towards one another, so maintaining a ratio of 3 females for each male is preferable. Having multiple females is also better for their health: a male with only one female will attempt breeding so often that she will become stressed and may even die.
Mollies make a fantastic addition to a community tank as long as other fish are close to the same size and equally peaceful.
Any small peaceful community fish will get along well with Mollies. Some possible tank mates for Mollies are:
- Other Mollies
- Cherry Barbs
- Corydoras Catfish
- Dwarf Gouramis
- Harlequin Rasbora
- Rosy Barbs
- Yo-yo Loaches
- Zebra Loaches
Species of shrimp and snails are another popular option for tankmates that Mollies will ignore.
Molly Fish General Behavior
Mollies are peaceful, social fish, making them great choices for a community tank of other amicable fish. The only aggressive behavior stems from males pursuing females for mating. Males kept without females have been known to become aggressive, nipping fins of other fish.
Mollies prefer to have cracks, crevices, and plants to hide in but are not generally very shy.
How to Keep Molly Fish Healthy
Mollies are incredibly hardy but can be susceptible to typical ailments that affect freshwater fish, especially in environments of lower water quality or sudden changes.
Common diseases to look out for
Like most aquarium fish, Mollies are susceptible to ich, a disease caused by protozoa. Symptoms of ich include twitching, rubbing their bodies on various surfaces in the tank, and the appearance of white spots on the body and gills. They usually respond well to medication and heal quickly.
Swim bladder disease is an ailment characterized by abnormal swimming patterns and trouble maintaining buoyancy. This can be caused by genetics, improper nutrition, overfeeding or constipation, a physical deformity or even an infection. Some cases are successfully treated by feeding defrosted frozen peas.
Mollies can be affected by skin flukes and other parasites, fungal infections, and bacterial infections.
When treating an individual fish, best practice calls for removing the fish to a separate “hospital tank” devoid of plants or gravel for treatment. If a disease has affected an entire tank, it is probably best to treat the tank. Read and follow the instructions for any medication or treatment for best results. Take care, as some treatments can destroy beneficial bacteria or otherwise adversely affect water quality. The carbon in your filtration system may absorb some medications, rendering treatment ineffective, and may need to be removed.
Know the signs and treatments of common freshwater fish diseases to catch problems early and keep your Mollies happy and healthy.
Tips on keeping Mollies in good health
Mollies are typically easy to keep healthy as long as you monitor and maintain your water composition. Perform water changes and test water quality regularly to keep ammonium and nitrite levels in check, and do not overfeed as food waste will cause these levels to spike.
Keep in mind that parasites and bacteria can be introduced by new tank mates as well as live food, plants, and tank decorations.
Most varieties of Molly breed exceedingly well in captivity. Mollies are live-bearing fish, meaning females gestate eggs inside their bodies and produce live, developed offspring. A tank of mixed-sex Mollies will almost always perpetually produce offspring, but if the fry are not removed the majority will quickly be eaten by adults. Females and males should be kept in a ratio of 3 to 1 or more to prevent the male from harassing the females.
Fry can be protected by providing floating plants or dense plants like Java moss for the babies to hide in. The more plants your tank has, the more likely some of your fry will live to adulthood.
Interesting Facts About Molly Fish
- Mollies are capable of surviving in both fresh and saltwater environments.
- Color patterns and variations are seemingly infinite due to breeding and hybridization.
- Mollies don’t lay eggs, they produce live offspring.
- Larger mollies can produce up to a hundred babies at a time.
Are Molly Fish right for you?
Mollies are arguably one of the easiest fish to care for. They are aesthetically-pleasing, social, and peaceful aquarium fish that get along with most other community fish. Most Mollies tolerate a variety of water conditions, making them an easy-keeper for someone new to the hobby.