One of the most popular aquarium fish found at pet stores are mollies because of their wide selection of colors, energetic behavior, and ease of breeding. If you are looking for a livebearer (or fish that bears live young) that is bigger than a platy but smaller than a swordfish, then mollies strike a happy medium. While molly fish are fairly easy to care for, beginners sometimes struggle with them, so find out the secret to caring for mollies and successfully breeding them in your home.
What are Molly Fish?
This prolific livebearer is found in freshwater, brackish, and saltwater habitats ranging from the Southern United States to Columbia. They have a more streamlined body compared to platies and can reach up to 4-5 inches (10-13 cm) in length. They are surprisingly good at cleaning aquariums, constantly scavenging for leftovers and pulling off hair algae with their flat mouths.
What are the different types of mollies? The most common species in the aquarium trade include Poecilia sphenops (short-fin molly) and Poecilia latipinna (sailfin molly). Hybrids have been selectively bred to create black, dalmatian, lyretail, balloon, gold dust, marble, platinum, creamsicle, and other variations.
Mollies are very popular because they come in a multitude of colors, patterns, and shapes.
Do mollies need salt in their water? Many fancy mollies are bred in overseas locations where salt water is cheaper than fresh drinking water. Therefore, the fish farms often raise them in brackish water that has both high pH and GH (or water hardness). When these brackish-bred mollies are transported to wholesalers, fish stores, and home aquariums that use fully freshwater setups, the change in water parameters can cause their kidneys to shut down. If you have naturally hard tap water, your mollies may not have any problems, but if you have soft tap water that lacks minerals, they may develop diseases like ich (white spot disease), fungus, and livebearer disease. For people with soft tap water, we suggest adding Wonder Shells or Seachem Equilibrium to increase the amount of calcium, magnesium, and other beneficial minerals in the fish tank.
How to Set Up an Aquarium for Mollies
Depending on the type of molly fish, we recommend getting an aquarium that holds at least 20 gallons of water, but a 29- to 55-gallon tank is more suitable for larger species. For most homes, they require an aquarium heater to raise the temperature to 75-80°F (24-27°C). Given their high tolerance for salt, they also prefer higher pH, KH, and GH.
How many molly fish should I have? As with many livebearers, mollies love to breed, so we recommend getting at least two to three females for every male. This ratio allows the girls to get a break from the boys’ constant attention. (A male can be identified by his stick-shaped anal fin called a gonopodium, whereas a female has a fan-shaped anal fin.)
Female (left) and male (right) sailfin mollies
Do mollies nip the fins of other fish? Generally speaking, mollies are peaceful fish. However, they are very active and often nibble on things to see if they are edible. Therefore, slow-moving, long-finned fish may not be the best tank mates for them.
What fish can you put with mollies? They do well with other community fish that live in similar environmental conditions and are close in size to avoid predation. We’ve had success keeping ours with cory catfish, danios, tetras, loaches, barbs, and other livebearers. Avoid putting larger mollies with smaller animals like cherry shrimp because they will most likely get eaten.
What do Molly Fish Eat?
Mollies are not picky eaters and are first in line to gobble up anything you drop in the aquarium. Because they are omnivores, provide a good mix of proteins and vegetables in the form of high-quality flakes, pellets, frozen foods, and Repashy Soilent Green gel food. If the mollies often have long strings of normal-colored poop hanging from their bodies, you may be overfeeding them and need to cut back their portion size. Also, if you find they are outcompeting other fish for food, consider feeding fish foods that scatter all throughout the tank to give other animals a chance to eat.
Balloon mollies are bred to have a rounder shape, so check the amount of waste they produce to see if you are overfeeding them.
How to Breed Mollies
Hobbyists joke that all you need to do is add water and livebearers will multiply. Just make sure you have at least one male and one female, and then wait 30 to 60 days for the baby fish to arrive. A new female may only give birth to a handful of fry, but a veteran mom can produce more than 50 offspring at a time. The adult mollies will predate on their own young, so increase their survival rate by providing lots of dense aquarium plants like water sprite, water wisteria, and Pogostemon stellatus ‘octopus’ as hiding spots.
Baby mollies may be born with relatively drab colors at first, but they will quickly develop the vivid hues of their parents.
Compared to the tiny fry that hatch from eggs, livebearer fry start off much bigger and able to eat crushed flakes, Easy Fry and Small Fish Food, Repashy gel food (in powder form), and live baby brine shrimp. Depending on the water temperature and amount of food eaten, it may take four to nine months for a baby molly to reach juvenile size and be ready for rehoming. Learn more about how to sell your extra mollies in our article on How to Breed Aquarium Fish for Profit.