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Contents
Overview
The molly is one of the best-selling livebearers in the hobby. Wild fish come from rivers, lagoons and estuaries in Mexico and Central America, but what you find in stores are almost always captive-bred strains, often mixed with other Poecilia species: black, dalmatian, gold, balloon and lyretail mollies.
People love them because they are active, curious and spend all day grazing algae off the glass and decor. They also breed readily, which makes them a classic learning fish. Mollies are a good beginner choice with one firm condition: they need hard, alkaline water. In soft, acidic water they get sick often, and that is where many first tanks go wrong.
Care and tank setup
A small group needs at least 26 gallons (100 L) and a tank about 30 inches (80 cm) long. Mollies grow bigger than guppies, produce a lot of waste and swim constantly. The tank must be fully cycled, with a good filter and a heater.
- Water: hard and alkaline. If your tap water is soft, raise hardness with mineral salts or crushed coral; a little marine salt is optional when hardness is already high.
- Ratio: one male to two or three females, because males chase females nonstop.
- Decor: hardy plants, open swimming space and a few hiding spots for females.
They do well with peaceful fish that like similar water, such as platies, swordtails and rainbowfish. Avoid soft-water species. Classic mistakes are water that is too soft, infrequent water changes and small tanks, all of which encourage fungus, ich and the well-known "shimmies." Never release mollies into the wild.
Feeding
Mollies are omnivores with a strong taste for greens. Use a quality flake or pellet with spirulina as the staple, and add blanched vegetables (zucchini, spinach, shelled peas) plus live or frozen brine shrimp or daphnia a couple of times a week.
Several small meals a day beat one big one. They graze algae all day, which helps keep the tank tidy, but it is no replacement for real food.
Breeding
Mollies are livebearers: females give birth to fully formed fry every four to six weeks, 20 to 60 at a time depending on size, and can store sperm for several broods. Adults eat the babies, so if you want to raise some, provide dense or floating plants as cover.
Fry take crushed flakes and baby brine shrimp from day one. Plan ahead for all those fish: a local store, other hobbyists or keeping one sex only.
Compatible tank mates
Species from our database that share water parameters, size and temperament with the Molly. Calculated from the data in each profile.
Bronze cory Corydoras aeneus 21 gal (80 L) · 72–81 °F (22–27 °C) 
Nerite snail Neritina natalensis 5 gal (20 L) · 72–82 °F (22–28 °C) 
Horned nerite snail Clithon corona 5 gal (20 L) · 72–82 °F (22–28 °C) 
Amano shrimp Caridina multidentata 11 gal (40 L) · 64–82 °F (18–28 °C) 
Cherry shrimp Neocaridina davidi 5 gal (20 L) · 64–81 °F (18–27 °C) 
Guppy Poecilia reticulata 14 gal (54 L) · 72–82 °F (22–28 °C) 
Yellow lab cichlid Labidochromis caeruleus 53 gal (200 L) · 75–82 °F (24–28 °C) 
Platy Xiphophorus maculatus 16 gal (60 L) · 68–79 °F (20–26 °C) 
Swordtail Xiphophorus hellerii 32 gal (120 L) · 72–81 °F (22–27 °C) 
Firemouth cichlid Thorichthys meeki 53 gal (200 L) · 75–84 °F (24–29 °C) 
Giant danio Devario aequipinnatus 63 gal (240 L) · 68–79 °F (20–26 °C) 
Pearl danio Danio albolineatus 21 gal (80 L) · 68–79 °F (20–26 °C) Check the compatibility of your whole tank →
What not to keep it with
Popular species you shouldn’t house with the Molly, and why.
- Discus: incompatible temperatures, incompatible pH, incompatible water hardness
- Oscar: incompatible pH, one may eat the other due to size, incompatible temperaments
- Ram cichlid: incompatible pH
- Rummy-nose tetra: incompatible pH
- Cardinal tetra: incompatible pH, incompatible water hardness
- Ember tetra: incompatible pH, one may eat the other due to size
Recommended equipment
What you need to keep the Molly healthy, checked against Amazon stock.
Frequently asked questions
How many liters does a Molly need?
At least about 100 liters for a group of at least 4 fish. More space always helps keep the water stable.
What water temperature does the Molly need?
Between 24 and 28 °C, with a pH of 7.5 to 8.5.
What fish can live with the Molly?
Based on water, size and temperament, it fits with species such as Bronze cory, Nerite snail, Horned nerite snail, Amano shrimp and Cherry shrimp. Use our compatibility calculator to check your whole tank.
Can the Molly be kept with shrimp?
Yes: it usually won’t eat adult shrimp, though some shrimplets may get picked off. A tank with plenty of moss gives the babies cover.