Molly Fish  (Poecilia sphenops)


            Natural Habitat of Molly Fish is spread across South Eastern parts of United States to South Eastern region of Mexico called the Yucatan Peninsula, they inhabit fresh, brackish & coastal waters. Molly Fish Natural Habitat are water logged areas, ponds, low current streams, swamps & ditches. In their natural habitat Mollies hang around vegetation to avoid being spotted by predators.


         There are three main species of Molly. Short-finned Molly, Sailfin Molly & Yucatan Molly.

Short-finned molly have shorter dorsal fin hence the name short-finned Molly.

Sail fin Molly  have a longer dorsal fin which almost touches the Caudal Fin or Tail fin, they have about 15 fin rays on their dorsal fin.

Yucatan Molly are the largest of  Mollies which can grow over 4 inches in length & have larger dorsal fin, they are distinguished from Sailfin Molly with the number of fin rays in their dorsal fin which is 20.

                Mollies that we find in Ornamental Fish Keeping Hobby are sub-species Captive Bred usually from short fin Molly & Sail fin Molly.Yucatan Mollies are difficult to breed & requires more care & attention compared to other Types of Mollies.

              Molly Fish in the wild have average life span of 1 to 2 years. The males have shorter life span than females.The male Molly reaches sexual maturity in less than year depending on their environment. However in an Aquarium they are known to live up to 5 years with proper care. 

             Mollies are Live-bearers & Prolific breeders. After mating once, female Molly can give birth even without the males presence multiple times. The gestation period is usually around three to four weeks.The brood size can vary between 10 to 140 fry depending on the size of the female & the surrounding condition. Molly fry are independent at birth. The female which gave birth may eat her fry. 

             Molly fish are omnivores in their Natural habitat, they eat algae, plant matter & aquatic larvae of insects.


Visual differences between Male & Female Molly

Male & Female Ballon Molly |

Male Mollies are usually smaller than Female Mollies; they have a modified cloacal fin under belly called gonopodium, this is used for mating. Fins of the Male are always longer in most strains.

Female Mollies are much larger than Males but the fins are smaller; they are some rounder in shape at the belly area. Coloration is also a little dull on females in most types of Molly strains. 


Molly Fish Aquarium Care

Chocolate molly |

Molly Fish is a Great Beginner Fish as they are hardy Fish & very easy to maintain. However like any other pet a little research would help. Mollies should be kept in a community tank with other Mollies or other Tank Mates like Zebra Fish, Platy Fish or Sword Tail. The best ratio of Mollies is One male for every three Females. Mollies can get aggressive if there are too many males in the Tank & also they can nip fins of other fish usually the ones with longer fins. I observed there is always an Alpha male in a Molly Tank. You might need to watch out for this alpha male, he might be aggressive to other fish. The below  information will help with Molly Fish Aquarium Care.


What your Molly Fish needs

Molly Fish |

Tank Size :  20 gallon or more (70 to 80 liters approximately). 20 Gallon can house 5 to 6 Females & 2 Males. The Bigger the Tank the better!. The Balloon Molly can be kept in a slightly  smaller tank with the same 1:3 ratio. 

Heater : Ideal Temperature should be around 75° to 80° F (23.8° to 26.6° C).  

Substrate, Plants & Rocks : Molly Fish tank has to have lot of plants, live plants look good & provide lots of  hiding spots for fish. 

Thermometer : This will help you monitor the temperature. Remember there should never be drastic changes in water temperature, you have to always maintain a steady temperature of  75° to 80° F (23.8° to 26.6° C). Lower temperatures can cause serious damage on Molly Fish health. 

pH test kit : pH level should be neutral 7.0 to 8.0. Chlorine free Tap water should be fine, however you never know if its too Acidic or too Alkaline, to avoid this get a pH test kit.

Lights : If you are planning on live plants in your tank, make sure you get suitable light for your plants. If you get artificial plants any small LED will do. Just make sure the light you install does not heat up the water in the tank too much. 

Filter/Air pump : Filtration is necessary for Molly tank. The Bio-Load is minimal however in case of over stocked tanks you might need a bigger n better filter.

Water conditioner : Tap water in most places are treated with chlorine. This is bad for your buddy. So get a water conditioner, this will make the water  'Molly Safe'.

Molly Fish food : Molly fish are Omnivores; they eat a variety of  readily available fish food, they like blood worms & brine shrimp. You can buy freeze dried worms from any Pet store, Pellets, Flakes Spirulina based food, live food like daphnia, mosquito larvae, micro worm etc, its advisable to feed them twice a day & feed only as much as they can consume in 2 or 3 minutes. 


Breeding Molly Fish

Sailfin molly pic _

Like any Live-bearer fish, breeding Mollies is easy; one healthy Male & few healthy Females in an aquarium with the right condition & you would see lot of fry every few weeks. Even if you are buying a fully gown Female Molly  from a Pet Store, chances are its already pregnant & you would see some fry in few weeks. Now the question is do females eat their fry? The answer is Yes & No, few females do eat their fry & few don't.

 Breeding mollies is easy in an aquarium, most hobbyist try to find ways to stop Mollies from breeding as they multiply very quickly, brood size may vary  from 10 to 140 . I tried this too it never worked; all Male Molly tank did not work as without female mollies, they went after each other; all Female Molly tank did not work as one female always dominated other females & harassed them by nipping their fins. The most peaceful Molly aquarium is the one with the ratio of at least 1 male for 3 females as the dominant alpha male seems always busy with female.


Caring for a Pregnant Molly Fish

Taking care of a Pregnant Molly fish in case you want to save the fry requires a Breeding Tank. The Tank Size can be 5 gallon for Balloon Molly & 10 to 15 gallon for a Short-finned or Sail-fin Molly.

A Sponge filter is recommended with live plants like Java Moss or any Floating Plants will help, next would be a heater depending on your location & lighting as per plant requirement. The Gestation period for a female Molly is around 30 days. After mating once with a Male, the Female Molly can give birth at least 3 times with each brood size varying from 10 to over 100 fry each time; this means you can expect to see new born fry every 5 to 6 weeks.

Female needs to be moved into the breeding tank, less than a week before she is ready to give birth, like you see in the video above. Make sure the water in the breeding tank is the same as the main tank she was moved from, without variation in water parameters.Sponge filter should have beneficial bacteria on it, you can run the sponge filter in the main tank for few days before adding it to the breeding tank. Feed the pregnant fish 3 times a day. Once the female gives birth you can remove her from the breeding tank as chances are she may eat the fry.

Other option is using a Fry trap or Breeding box which is available online to purchase, Female is kept it the breeding box in the main aquarium until she gives birth & then removed from the box. This way you can avoid cycling a Breeding Tank. Ensure to purchase a bigger Breeding Box as they usually end up being small for the pregnant fish & in case the brood size is big.


Molly Fry Care

Baby Molly fish need a little extra care for optimal growth and good survival rate, to achieve this they must be raised in a separate Nursery Tank Or Breeding Tank; tank size can be 5 gallon to 10 gallon depending on the size of the brood. You need good filtration system, so use a sponge filter which is fry safe. Add live plants floating or something live Java Moss or Moss Balls, heater maybe required depending on your location.

Once the fry are born they would feed on the yolk sac by observing it for a day or two, after which they are ready to be fed fish food. Brine shrimp, micro worms are their favorite, you can simply crush fish food you feed the adults small enough to fit in their mouth or simply buy micro pellets for fry from Pet Store or order it online. First week is crucial you would see fatalities, the weaker fry may die, strongest would survive; usually by day 3 or 4 the fry start consuming fish food.

Few things that needs to be followed for at least 6 to 8 weeks caring for the fry in the Nursery aquarium would be maintaining water parameters, I follow 25% water change every 3 days, I feed 3 times a day which is crushed flakes, mini pellets, brine shrimp, micro worms or mosquito larvae. 

Temperature should be on a higher side 78 to 82 degree Fahrenheit for Molly Fry. Molly fish prefer alkaline water condition around pH of 8. This plays an important role in keeping the fry healthy & gaining a optimal growth rate. 

Lights for Molly fry is important as it helps their natural pigmentation. Lights should be off for at least 8 hours for the molly fry to sleep, good sleep also helps with the growth rate.