How To Care For Molly Fish: A Complete Fact Sheet, Breeding, Behavior, and Care Guide

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Mollies are a small tropical fish that originate in freshwater streams and swamps – or, occasionally, the ocean. Since they are able to survive in either saltwater or freshwater, they’re a pretty unique fish that has become extremely popular with fishkeeping hobbyists over the years.

These little fish are livebearers – which means they give birth to their offspring, rather than laying eggs like many other fish species.

They’re extremely gentle-natured and come in attractive, vibrant colors of many shades.

Molly fish sound a little like they ought to be swimming in straight from Ireland – that name! – but Mollies are actually a collection of three species of fish originally from coastal regions around the southeastern United States, Gulf of Mexico, South America, and Central America. They’ve all been inter-bred and hybridized to the point that it’s almost impossible to tell them apart.

molly fish isolated on black background

The first species of Molly freshwater fish is the Sailfin Molly – or Poecilia latipinna – which specifically comes from the Gulf of Mexico areas along with southeastern United States. They are prolific breeders and do well in anything from freshwater to brackish water and even saltwater fish tanks. If you purchase a wild-caught Molly, it’s likely one of these.

The second species is the Short-Finned Molly – Poecilia sphenops – which adapts to aquarium life more quickly than the other Molly species. This makes them a fantastic option for newbie aquarists in particular. They also breed like crazy and tolerate just about any kind of water – except soft water. This is the other strongly likely species of Molly that may be wild-caught.

The third species of Molly is the Mexican Sailfin Molly or Poecilia velifera. This species is found in the coastal areas around the Yucatan peninsula and can also tolerate saltwater. They tend to be more difficult to keep in aquarium settings than the other two species, however, as they don’t breed in captivity nearly as well. This also means they are less likely to be found in captivity.

You’ll find a whole lot of other molly fish information to answer all of your questions about Mollies, like how long do molly fish live? Is Dalmation molly fish care any different from silver molly care or from black molly fish care? What is the average molly fish size? Or what are common molly fish colors?

Let’s dive deeper.

Quick Intro to Molly Fish

FamilyPoeciliidae
Scientific NamePoecilia sphenops, Poecilia latipinna, or Poecilia velifera
Popular Types of MolliesBalloon Molly, Black Molly, Sailfin Molly, Lyretail Molly, Dalmation Molly, Silver Molly, Dalmation Lyretail Molly, Black Sailfin Molly, White Sailfin Molly, Gold Dust Molly, Balloon Belly Molly, Gold Doubloon Molly, Harlequin Sailfin Molly, Platinum Lyretail Molly, Gold Sailfin Molly, Creamsicle Sailfin Lyretail Molly, Red Sunset Molly, Wild Molly, Orange Molly, White Molly Fish
Care LevelEasy

Natural Habitat, Identification, and Where to Buy

The natural habitat of a Molly can vary widely. As mentioned above, they are extremely adaptable and can live in freshwater, brackish water, or even saltwater and thrive.

The only issue they have with water is soft water – which is important to note for some other species of fish you may to keep them with. Interestingly enough, these little fish can tolerate high hydrogen sulfide levels as well.

Most often, Molly fish are found in shallow sections of rivers, streams, and swamps, in North, Central, and South America. They are most commonly observed moving through the shallows along the edges in these places, as well as lowland streams, ponds, estuaries, and marshes.

The natural substrate in these regions is sandy with rocks and debris on the top, which gives us a clue as to what kind of aquarium we should keep them in.

Because of where they live in the wild, Mollies are also surrounded by loads of aquatic plants naturally. The plants provide shelter and food for them, especially during the reproductive process. These rivers where they live are tropical or semi-tropical, so they get a fair supply of sunlight for plant growth.

Floating vegetation is often shelter under which these little fish live, which provides them with a protective shield against being spotted by predators.

The water where Mollies live is naturally slow-moving and warm, with a pH that tends towards slight alkalinity.

Sailfin Mollies are also capable of surviving in an oxygen-depleted environment. They’re able to use their upturned mouths to breathe in the thin film of oxygen on the surface of the water – which is how they can survive in saltwater habitats.

Molly Fish have a flattened body, with a “tall” center that narrows into a point at the mouth. They have large caudal fins that are fan-shaped and are either transparent or very colorful. The dorsal fin will have a similar shape or flatten against the body, depending on the Molly species.

Molly fish are livebearers and the females seem to almost always be pregnant, thanks to the voracious Molly fish breeding behavior. Females are larger than males and fairly easy to identify, especially because of that near-constant pregnancy.

And if you’re wondering how big do molly fish get, the answer is: up to 4.5-inches.

This size can also help you identify the Molly fish from another species of similar-looking fish if you’re not terribly familiar with them. Some species of guppies can look similar to Molly fish, but guppies are about half the size of Mollies when full-grown.

When you’re ready to buy Molly fish, you can find them in multiple places online for modest prices. Some of the best places to find a range of species and types include:

Optimal Water Conditions for Mollies

Molly Fish Temperature70°F – 82°F
pH7.5 – 8.5
Hardness10° to 25° dH

Tannin Recommendations

Tannins soften water. Mollies are hard water fish, so it’s important to completely clean your driftwood and other fish tank decorations that may contain tannins completely.

Monitor the GH and KH levels when you introduce anything new that may have tannins and scrub thoroughly again if the levels change after a change in the scenery.

Other Water Chemistry Needs

Mollies technically do fine in any water type save soft water. They thrive most in freshwater and brackish water aquariums, though they may survive in marine tanks if the water is treated properly.

dalmatian molly fish

Tank Setup

Minimum Tank Size15 gallons or 30 for sailfin species
Optimal Tank Size20+ per 1 molly with an extra 3 gallons per additional molly
Optimal Tank ShapeTall aquariums are ideal for mollies
Recommended Filter TypeAny – but go larger than you anticipate you’ll need

Extra Air Flow and How to Provide: Mollies do best with additional air movement in the aquarium. Add in multiple air stones – one per 10 gallons ideally – to help your mollies thrive.

Mollies that are bred in captivity are used to pretty much the same environment, so you won’t have to worry too much about needing a different setup from other tanks for fish with similar water chemistry needs.

Mollies are tropical fish, so they need their tank maintained at a warm enough temperature to keep them healthy and happy. They also need the hard water and pH levels in balance, whether you keep them in freshwater aquariums or brackish fish tanks.

Just remember to pair them with plants and fish that also need slow-moving water.

Creating the Landscape

Mollies do best with a sandy substrate at the bottom of the tank – this most naturally resembles their natural environment – and loads of live plants will provide them with the shelter they need. The plants also help with a variety of other issues – like helping them find algae to eat – and add a lot to the aquarium overall, anyway.

Mollies really do hang out in all regions of the tank, so having taller plants like Anubias can really help benefit them when they need to hide.

They also thrive with rocks and caves or crevices where they can hide. Since they’re prolific breeders and very social fish, they tend to need a little extra protection if they have any tank mates that aren’t shy.

As to lighting, they need medium to bright light – though medium is their ideal. This provides the plants they love with enough light for photosynthesis without causing too much algae growth – though Mollies do love to nibble on some algae – and make the maintenance of the aquarium easier for you.

The plants not only provide the shelter they need, but they also give Mollies a food source.

Mollies are medium to small fish, depending on their exact environment, so they need loads of room for swimming. They’re used to living in shallow water, but they do love tall tanks where they can reach the surface and pull in that air.

Best PlantsVallisneria, Sagittaria, Najas – or Guppy Grass – Hornwort, Duckweed, Anacharis, Anubias
Best LightingMedium
Best DecorationsMollies do best with sandy substrate. They hang out all over the tank, but often drop to the bottom to hide out in the plant base. Provide them with crevices, caves, or other rocks for additional hiding spots.
Decorations to AvoidAnything with sharp edges – especially if you have Sailfin Mollies. These sharp objects can snag and cut their delicate fins and cause severe health issues and physical harm to the fish.

Physiological Considerations

Maximum SizeUp to 4.5 inches
Rate of GrowthMollies will reach sexual maturity around 3 to 4 months of age
LifespanUp to 5 years
TemperamentPeaceful
Preferred Tank RegionAll regions
Scale ThicknessCan be harmed by sharp objects in their homes. Avoid substrate with sharp edges or rocks that haven’t been rounded and smoothed.
Gill ConsiderationsMollies live in slow-moving water so they should be kept in slow-moving water situations for the optimal health of their gills. This can help to keep them disease free.
Swimbladder ConsiderationsMolly fish have standard swim bladders. This means they are particularly susceptible to issues with overfeeding – look for the bloating of bellies – and swim bladder disorder.
Fin Shape ConsiderationsThe species of Molly that you stock will have different fin shapes. Sailfin Mollies have especially sensitive fins compared to the Short-Finned Molly. They should not be stocked with fish that nip at the fins of other fish.

The average molly fish lifespan ranges between three and five years.

This assumes that the Mollies have proper water conditions and proper care. Some species – like the Balloon Molly – will experience a shorter lifespan, thanks to the inbreeding that creates a natural spinal disfigurement, creating the balloon shape.

And while the various species of Molly fish do have some differences in the details, they all generally require the same Molly fish tank set up, and the same basic care.

The primary differences are going to be in the amount of food one species needs from another – larger fish generally need more food than a smaller fish – and how carefully you need to monitor their fins.

Society

Molly fish behavior by nature, is peaceful and social, though males can be a little aggressive towards other Molly males, so it’s a good idea to provide a single male with a mini harem of three females each. Having multiple females can also help the general health of the fish overall, as Mollies are worse than rabbits. A single male will attempt to breed with a single female many times – sometimes to the point of overexertion for the female, resulting in severe tress and even early death.

Mollies are great fish for community tanks, as long as their tank mates are close to them in size and equally peaceful temperament.

Be sure to feed any existing fish in your aquarium before adding a new Molly to the fish tank. This will help to protect the new fish from potential attacks from any fish that feel threatened or scared by a new tankmate.

Mollies are a peaceful community fish over all, so they will get along with other small to medium community fish that aren’t larger than the Mollies.

Some ideal Molly fish aquarium mates include:

aquarium swordtail with a molly fish

Gender, Breeding, and Reproductive Considerations

It’s actually pretty easy to tell Mollies apart – male from female. Males have modified anal fins and tend to be slender, while females are a little rounder in shape. Male Sailfins will be especially easy to identify, as they have the sail dorsal fins and females do not. This is only true in males over two years of age, however.

If you’re looking to have more Mollies, breeding them is not exactly what you’d call hard, since these guys are prolific and have loads of babies all at once.

Mollies do need a tank of at least 20 gallons per Molly fish mating pair if you’re attempting to breed them. It usually takes between 40 and 70 days for the gestation period to complete.

And if you’re asking, “how many babies do mollies have in a single pregnancy?” You might be surprised to learn the answer is: a dang lot. Female Molly Fish will bear at least 20 live young Mollies, though they can have up to 60 live fry that they give birth to.

If the female’s belly becomes extremely distended – assuming you know she’s pregnant – she’s about to give birth. It’s important to provide a quiet, peaceful place for her to give birth. Male Mollies and other community fish in your tank can cause stress for the soon-to-be mother, so it’s important to protect her. If she gets overly stressed, she may have miscarriages and/or stillborn fry.

The best way to proceed with breeding is to have a separate breeding tank for your Molly. This not only helps to make sure the Mollies breed, but it protects the female once she’s pregnant. The fry will also be safer once they’re born. This is one of the best methods for your molly fish babies care and protection.

If, however, you can’t provide a separate breeding box, you can allow your females to remain in the main aquarium if there are enough plants to help her hide and protect the babies once they’ve been birthed.

Nutritional Needs

Mollies are omnivores by nature. They also tend to eat just about anything that comes their way, so it’s important to make sure the food provided to them is healthy, natural, and balanced.

They will eat the plants in their aquarium – so be sure to only house them with plants you don’t mind having munched on. Replace them as often as needed to keep the tank well-planted and healthy.

Variety is important for your Molly’s health. Protein is important, but so is vegetation. Expect to feed them a combination of high-quality foods ranging from produced options like low-starch flakes and pellets to vegetables, blackworms, and brine shrimp.

Mollies specifically are known for overeating, so it’s very important to remove any excess food immediately from the water after a feeding.

Mollies especially do well with a combination of prepared foods, protein treats, and vegetables. Some of their favorites – that also help with their coloration and improve their health – include:

  • Cucumbers
  • Zucchini
  • Spirulina
  • Frozen bloodworms
  • Freeze-dried bloodworms
  • Frozen brine shrimp
  • Freeze-dried brine shrimp
  • Algae wafers
  • Peas
  • Green beans
  • Daphnia
  • Blackworms
  • High-quality flake food
  • High-quality pellets
  • Live plants in their aquarium

Mollies should eat two or three times per day.

Best Sustenance Food TypeA combination of low-starch (no-grain, preferred) flake or pellet food, along with a mix of freeze-dried brine shrimp, spirulina, and frozen bloodworms.
Additional Food for Optimal HealthBlackworms, bloodworms, Daphnia, brine shrimp, spirulina, algae wafers, romaine lettuce, green peas, string beans, zucchini pieces, cucumber.
Special Foods and Considerations for Best Color and GrowthA healthy balance of the vegetables, flake or pellet food, and protein treats will help your Molly have bright, vibrant colors and healthy scales, eyes, and gills.
When and How Often to Feed Fish Based on Life CycleFeed them 2 to 3 times per day, with only enough food each time that they can consume it all within two to three minutes. Remove any uneaten food immediately to avoid swim bladder issues and other health problems.

Common Diseases and How to Avoid and Treat Them

Aquarium fish are susceptible to Ich, a disease caused by a nasty little protozoa. Molly fish are no exception to this tendency.

Symptoms of Ich include:

  • Twitching
  • Rubbing their bodies against surfaces of objects in tank, as if scratching themselves
  • White spots appearing on the gills and body

Mollies are also susceptible to swim bladder disorders and diseases, especially because they have a tendency to overeat. You’ll notice this issue if you pay attention. They tend to have abnormal swim patterns, distended bellies – when not pregnant – and difficulty maintaining buoyancy.

If you notice any of these symptoms – especially in combination with each other – your little Molly probably is suffering from swim bladder disease and needs some medical attention. Interestingly enough, feeding thawed out frozen peas can actually sometimes help treat this problem.

Other issues Mollies may have also include skin flukes and other parasites, bacterial infections, and fungal infections.

Best Antibiotics: Any antibiotic that is safe for a Molly fish.

Treatments to Avoid: Generally freshwater fish treatments should be safe for these healthy little fish.

Food Recommendations When Sick: Thawed frozen peas may well help with some of the various health issues.

Hospital Tank or Isolation Within the Community Tank Specifics: If Mollies become ill with parasites or other ailments, they should be removed from the community tank and kept in a hospital tank with no plants, gravel, and other fish.

black molly fish in an aquarium

4 More Things to Know About Molly Fish

  1. Mollies are an unusual species in that they can live in anything from freshwater to saltwater like in the ocean. Most fish can only survive in one or the other.
  2. Mollies have a huge array of coloring choices, thanks to specific breeding, hybridization, and the mere fact that they are intensely prolific breeders.
  3. Molly fish are livebearers, not egg-layers, making them distinct from many of the other popular aquarium fish you might choose to keep.
  4. Some species of Mollies – the largest species – can actually give birth to over 100 babies at a time. More commonly, the minimum is 20 babies in one pregnancy, with a “normal” maximum at 60 babies at once.

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