Mollies And Guppies: Are They Happy Together In One Tank?

Last Updated: October 22, 2023 by Flora Gibbins

Mollies and guppies are two beautiful fish of the same genus. These tropical fish are popular among aquarists because they are vibrant, colorful, and easy to care for and breed. 

You must be wondering whether guppies and mollies can share a tank. The answer is yes. These aquarium fish have similar temperaments, diets, and water parameters.

This article will discuss in length factors that make mollies and guppies suitable tank mates. Read on.

A Quick Overview of Mollies And Guppies

This table offers you a glance at the similarities between guppies and mollies. 

Mollies And Guppies: Temperaments

Both guppies and mollies are peaceful fish species. But under certain conditions, these fish can get aggressive. Let’s take a closer look at each species.

Guppy Temperament

Guppies mind their own business and rarely bother other tank mates. Nevertheless, you may observe aggressive behavior from the males. 

Having too many male guppies in a community tank will force them to fight for reproduction rights. Since the law of nature dictates survival for the fittest, only the healthy and vigorous male guppies will mate with females.

Unfortunately, the constant aggression to mate can stress a female.

To avoid this, the male-to-female ratio should be 1:3. The higher the number of females, the better. 

Molly Temperament

Mollies are peaceful when kept in the right conditions. If you provide enough space for these active fish, they will be generally happy. However, overcrowding the tank will make them aggressive. 

Therefore, if you keep mollies and guppies in the same aquarium, it should offer enough room for both species. Failure to do so will see the mollies nip the long, flowing fins on a male guppy.  The males are often more colorful than females. 

Like guppies, keep more female mollies than males. The males can also get aggressive with each other. So, have one male molly fish for three females. 

Mollies And Guppies: Tank Requirements

Mollies and guppies are hardy fish that live in similar habitats and tropical water temperatures. Both fish can live in brackish water and fresh water. Let’s start with the right water parameters for mollies.

Molly Tank Conditions

Molly fish are adaptable and can survive in different environments. In the wild, these fish prefer shallow rivers and streams with vegetation and sandy substrate. This means you should provide a heavily planted tank. In terms of water temperatures, mollies are happy when the temperature is between 75 to 82 degrees F.

The pH levels should be between 6.8 to 7.8. You can keep them in brackish waters or freshwater. 

Mollies prefer their minimum tank size to be 20 gallons. Mollies are naturally active and love to swim a lot. These fish become aggressive when there is not enough space which is why a 20-gallon tank is perfect for keeping three mollies. If you want to add more fish, provide three gallons of water for each molly. 

Guppies Tank Conditions 

Guppies, on the other hand, do not require this much space since they are slightly smaller than mollies. The minimum tank size for guppy fish is 10 gallons. They will happily swim around in this space, but should you get a bigger tank, they will thank you for it. 

The preferred temperature for guppies is 74 to 82 degrees and a pH of 6.8 to 7.8. This temperature range and pH perfectly match the molly’s, meaning they can live in the same tank.

Guppies also enjoy a well-planted tank with lots of hiding spots. You could add live plants, artificial plants, driftwood, caves, or ornaments. 

To successfully keep guppies and mollies, get at least a 30-gallon or a larger aquarium. The fish tank should hold live plants and provide enough swimming space for the two species. 

You do not need to buy a heater if you live in a tropical climate. The weather in the tropics matches what these fish need.

However, if you do not live in the tropics, an aquarium heater will help stabilize the water temperature. Sudden water changes stress both fish and can make them sick. 

Check out our article for more details on guppy care.

Mollies And Guppies: Diet

Guppies and mollies have the same diet. Both are omnivores and prefer a diet of meat and vegetation. 

These fish will nibble on the live plants present in the tank and algae. In addition to this, remember to offer blanched vegetables, fish flakes, and live foods such as brine shrimp, mosquito larvae, or daphnia. Live food helps supplement your fish’s diet in terms of fiber. 

Should you feed bloodworms to guppies and mollies? Yes, but as a treat. Bloodworms are rich in fats which can be problematic if fed daily. 

Did you know mollies and guppies are opportunistic feeders? They always appear hungry (do not fall for this). Both fish have no trouble spending their days eating and eating some more. 

Overfeeding can pollute the tank water and lead to constipation and health problems. We highly recommend that you feed small portions of food that last for two minutes. 

Mollies And Guppies: Breeding

Guppies and mollies are proficient at breeding, so be prepared to have fish fry every month. If you are looking to raise molly fry and guppy fry, transfer the breeding pair to a breeding box or a separate tank. Let’s break down each fish’s breeding cycle.

Female guppy fish breed every 30 days. They do not lay eggs but give birth to guppy fry. 

A female molly can give birth to 10 to 60 baby fish a month. This means your 20-gallon tank may become overcrowded in just a few months. 

On the other hand, female guppy fish are livebearers, too. Guppies breed every 30 days, too, to 20 – 50 babies. Keeping guppies and mollies together means you have to think about population control as months go by. 

Both mollies and guppies do not always need male fish to reproduce. A female molly can save and store sperm for three months. Meanwhile, a female guppy can do so for a lifetime.

The absence of male fish does not mean the female mollies and guppies will not reproduce. Do not be surprised if the female fish you got from the pet store are pregnant, yet you do not own any males. 

But you can practice population control using one of these three tricks below:

Introduce Only Male Or Female Fish In Your Tank

If you keep male mollies with male guppies, they will never breed. The females you choose, however, should not have mated. This is because once they do, they store sperm for future reproduction. 

Keep Water Temperatures On The Low End

These fish love to breed when the water is warm. If you maintain the water temperatures at the lower range, they will be less active to breed. 

Allow Adult Fish To Eat Their Own Fry

Both guppies and molly fish eat their own fry. So if you are not looking to raise baby fish, you can allow the adults to manage the population. 

Guppy And Molly Fry Care

Guppies and mollies eat their young when they share the same tank. If you want to raise some baby fish, move the pregnant females from the main aquarium to a breeding box or a separate tank. 

Once the female releases the live fry, move it back to the community tank. Feed these little fish crushed fish flakes or buy fry food from the pet store.

The babies may take up to three months to mature, but you can promote their growth by maintaining the water temperatures at the higher end. 

Here is a quick YouTube video on how to differentiate molly and guppy fry:

Can Guppies And Mollies Interbreed?

Yes. You can breed guppies with mollies. The two fish belong to the same genus, even though they are different species.

Guppies and mollies are like horses and donkeys or lions and tigers. Both fish would rather reproduce with their own kind. But, if they do not have access to members of the opposite sex from their own species, they can reproduce with other species of their genus. 

What this means is that if you have male and female mollies in your tank or male and female guppies, do not expect to interbreed. Attempts to breed mollies and guppies almost always prove futile. However, if you keep male and female fish from different species, there is a slight chance of potential cross-breeding. 

When guppies and mollies breed, the offspring takes the guppy’s beautiful colors and a molly’s body shape. But they have a shorter lifespan and are infertile. 

How To Successfully Maintain Molly And Guppy Fish Tanks

We know that mollies and guppies are very similar fish that can live in the same aquarium. Even then, you should meet certain tank conditions and water parameters for both fish to live happily: 

1. Use A Larger Aquarium

The bigger the aquarium, the happier your fish will be. We recommend a 30-gallon tank as the minimum tank size for three mollies and three guppy fish. Mollies get aggressive when there is little room and will compete to dominate it. 

2. Make Frequent Water Changes

Both fish need their tank free of nitrites and ammonia to stay healthy like other fish species. Also, vacuum food waste, fish waste, or dead fish from the aquarium. 

Always perform a 30% water change every week. 

3. Maintain Stable Water Parameters

The ideal water temperature for guppy fish and mollies should be between 72 and 82 degrees F. They prefer a pH of 6.8 to 8.0 and are comfortable in brackish and freshwater. 

4. Avoid Overfeeding

These aquarium fish always appear hungry, and this may drive you to feed them too much food. The excess food can lead to waste build-up and health problems for the fish.

You can prevent this by feeding small portions of food that the fish can consume in less than five minutes. 

5. Include Hiding Spots

Also, add plenty of hiding spots. The fry, juveniles, and adult fish love to hide in densely packed plants. Plants also help oxygenate the water, and their leaves are part of the fish’s diet. 

Conclusion

Guppies and mollies are very similar fish. They are both peaceful fish that can live with other fish. Guppies and mollies live in the same water parameters and eat similar foods. 

Moreover, both species are prolific breeders and will fill your tank with guppy fry in no time. What’s more, since the two fish belong to the same species, they can interbreed. 

So, if you are not prepared to care for baby fish, take the necessary precautions before you bring mollies and guppies home.