Mollies are often thought of as relatively good tankmates for bettas. Their fairly placid nature and robust qualities do make them potential candidates, but there could also be some issues keeping these two species in the same tank together.
Should you keep mollies and bettas together? Sometimes yes, sometimes no. That depends a lot on your level of understanding and planning, and that’s what this article is here to help you to do.
First of All, What Are Mollies?
Mollies are a group of popular aquarium fish that hails from South, Central, and North America. The most frequently kept breeds include Black mollies, Sailfin mollies, Dalmatian mollies, and Lyretail mollies.
Like guppies and platies, mollies are livebearers, meaning they give birth to live young rather than laying eggs. They are rather prolific breeders and can multiply very rapidly if both males and females are present!
Mollies generally grow to around 3–4.5 inches, with some variation between different breeds and females growing larger than males. They come in a wide variety of shapes and colors and typically live to 3-5 years of age.
Mollies are often regarded as a good choice for beginner fishkeepers owing to their reputation as peaceful fish for a range of community tank setups.
Bettas and Mollies in the Same Tank?
It’s not easy to find tankmates for your betta. His aggressive tendencies and long, flowing fins make him a potential threat and a potential victim at the same time!
Some fish keepers have had positive experiences keeping mollies with bettas, while others have reported difficulties. Let’s look at some of the plus points as well as some possible drawbacks of keeping these two species together…
Some Reasons Mollies May Make Good Tank Mates for Bettas
If you’re looking for a tank mate for your betta fish, there are a few reasons why a molly fish may be a good option.
Mollies are very tolerant of a wide range of temperatures in the aquarium, from 72 – 80 Fahrenheit. This overlaps nicely with the betta’s preferred range of 78-80 Fahrenheit, so the two species are quite compatible in terms of temperature.
Mollies like the tank’s water to be neutral to alkaline, with a pH of 7-8.5. Bettas typically prefer water a little softer than this, with a pH of 6.5-7. A tank kept at pH 7, therefore, should satisfy the pH requirements of both species.
Most freshwater fish do fine in an aquarium without any additional salt. Mollies, however, often come from brackish waters and the addition of aquarium salt is sometimes recommended, at a dose between 3-6 ppt (parts per thousand).
This might seem incompatible with bettas, who are normally kept in unsalted water, but you may be surprised to know that some fish keepers are now keeping their bettas in slightly salinated water as an aid to their betta’s health.
Bettas also evolved in a variety of water conditions, including slightly saline, where various bacteria and fungi pathogens struggle to survive.
In short, a low dose of aquarium salt of 3ppt should keep both species happy, but freshwater without any salt is also fine. Molly breeders have run very successful operations without the use of any aquarium salt, although it may help to prevent diseases in some instances.
To read more about the addition of aquarium salt for betta fish, read this fascinating article published by the International Betta Congress here.
Bettas need tankmates that are both peaceful fish and also robust enough to deal with any potential aggressive outbursts. Mollies are substantially larger than bettas, and are strong swimmers, meaning they should be able to keep themselves out of harm’s way should your betta take an occasional lunge for them.
They do need a large enough tank to escape from any menacing attacks though, and I’d definitely recommend a tank of no less than 30 gallons to house both species. Rocks and plants will also help your mollies feel safe and provide hiding places should they feel threatened.
Male mollies can be rather boisterous towards each other but are usually more benign in their attitude towards other species. Having said that, each individual will have their own particular quirks and temperament, so please read more on potential problems concerning aggression in the section below!
Mollies are omnivorous in their diet and enjoy a mixture of meat-based proteins as well as plant material. They accept dried, live, or frozen foods and will also happily graze algae from the aquarium’s rocks and plants.
Bettas are more carnivorous in nature, but there is enough overlap in the diet of both species that they can generally be fed together without problems.
Mollies will enjoy tucking into the brine shrimp and bloodworms that your betta gets fed, while your betta may also accept the completely dried foods given to your mollies. A bit of vegetable fiber may even do your betta’s digestion some good!
Feeding time could stimulate a sense of rivalry between species though, so be sure to keep a watchful eye out when offering food to ensure there’s no serious aggression from either party.
Reasons Why Mollies May Not Make the Ideal Tankmates for Your Betta
While there are many good reasons mollies and bettas can make great tankmates, there are also some things to take into consideration that could prevent them from getting along.
Problem 1: Aggression
As we’ve mentioned, mollies are generally peaceable fish and are fairly tolerant of other species of fish around them. That’s only a generalization though and not to say that a molly would never harass your betta or nip his fins.
Male mollies can get quite feisty at times, especially between each other. Even if they ignore your betta, just the fighting between the male mollies may stress your betta, which should always be avoided.
On the other side of the coin, bettas may be excited into action by the bright colors and long fins of your mollies.
Male betta fish, also known as Siamese fighting fish, are renowned for tearing up the long, brightly colored fins of their opponents in battle. This means there’s always a chance that other species with long, flowing fins could trigger this same fighting instinct in them.
Male mollies are especially vibrant with longer fins, and so are at extra risk of attracting unwanted attention from your betta.
How To Lessen the Aggression Between Mollies and Bettas
Thankfully, there are some ways to handle this problem and still let your mollies and bettas live on as tankmates.
First and foremost, we need to talk about tank size. The main cause for aggression to become a problem is a lack of tank space, and fish encroaching on each other’s territory.
The minimum size tank for a single betta is 5-10 gallons. The minimum-sized tank of a small shoal of mollies is around 20 gallons. To keep the two species together you’ll need at least a 30-gallon tank, with larger tanks further minimizing the chances of aggression between species.
The tank should have plenty of plants and hiding places for the species to avoid one another and to landmark their own territories.
Understand Individual Differences
Just like with people, each fish has its own unique character. A great fishkeeper stands apart from a mediocre fishkeeper by the level of attention he pays each fish.
If you have an aggressive betta, think twice before introducing other tankmates. Try out a snail or a ghost shrimp with him to see how he will react before adding potentially vulnerable tankmates like mollies.
If you already have a tank of mollies, watch them very closely to see how they interact with one another. If you identify provocative individuals, consider moving them to another tank or giving them to someone else. Much better to have one less fish than a tank full of stressed fish suffering from one individual!
Introduce New Fish With Great Care
When it comes to aquarium fish, first impressions are extremely important! If a fish gets dumped in a new tank without adequate care, it may suffer from shock and be prone to persecution from existing tankmates.
This can start a vicious cycle, with the new fish becoming increasingly insecure and taking the role of the tank’s victim.
Giving a thoughtful and caring introduction to a new tank is a critical step to avoiding this. Whether you’re adding some mollies to an existing betta tank or introducing a betta to a shoal of mollies, take the time to give the new fish the best possible introduction.
Turn off the tank’s lights before floating the bag with the new fish in, and add tank water to the bag gradually to acclimatize the new fish to the tank environment.
Once acclimatized, release the new fish during the evening to allow them a night to get settled into their new home. In the darkened environment, unwanted attention from existing tank members is lessened. By morning the newcomers should feel more settled and ready to confront or escape from troublesome encounters.
A Different Combination of Sexes
Male mollies are typically more aggressive than female mollies. Likewise, a female betta is much more peaceful in comparison to a male. If you’re worried about aggression from your mollies, go for an all-female shoal, or at least provide each male molly with three females to keep him satisfied.
If, on the other hand, you’re concerned that a male betta fish might cause trouble in your existing tank of mollies, you can always try introducing a female betta instead.
Females of both species are often less showy than their male equivalents, but female bettas and mollies can still be very attractive in their own right. An all-female tank of both species would still make a worthy display and could cause everyone (including you) less stress in the long run!
Choose a More Peaceful Male Betta
Some fish keepers will understandably give priority to the vibrancy and beautiful displays of male bettas. As we’ve said, each male betta will have its unique temperament.
If you can get to know a male betta in his own tank and establish that he is unlikely to attack his tankmates, you’re more likely to have a smooth experience when you introduce your mollies.
If you’re introducing a betta to an existing tank of mollies and don’t have the chance to get to know him first, consider buying a Betta imbellis, or ‘Peaceful Betta’ instead. This is also a beautiful fish and tends to be more tolerant of tankmates than the usual choice, Betta splendens.
Choose a More Peaceful Type of Molly
There are more than 40 types of molly to choose from, and some are more compatible tankmates for your betta than others.
Black mollies and Balloon mollies have a reputation for being more aggressive than other kinds and may nip the fins of one another or even those of your betta. Balloon mollies have also been bred to have an unnatural curvature in their spine which makes them more prone to disease – never a good thing to encourage in your tank!
Sailfin mollies on the other hand can get extremely big! A six-inch specimen may dwarf your betta and make him feel stressed and vulnerable. They also demand a larger tank.
Dalmatian mollies and Short-finned mollies may make better choices since they’re not especially large or aggressive, and come without long, trailing fins for a betta to nip at!
Improve Your Tank Care and Maintenance
If your fish are not well cared for and become stressed, they’re much more likely to become antagonistic towards each other.
Mollies and bettas both need proper care, with the right water parameters and a regular cleaning schedule to remain healthy and happy.
If you notice aggressive behavior or anything indicating that your fish are stressed, ask yourself if you’ve properly attended to all of their needs including their diet, water temperature, pH, and all-around cleanliness.
Try out new additions to their diet. If you have no algae growing in your tank, try offering your mollies some algae wafers. If your betta is not looking at his brilliant best, treat him to some bloodworms or brine shrimp to see if that revives him.
Change part of your tank’s water often and keep a close eye on all tank members before problems get out of hand.
Problem 2: What to Do if Mollies Have Too Many Babies?
Mollies are prolific livebearers and can reproduce at an alarming rate. If you have both male and female mollies you may quickly have more baby mollies than you know what to do with.
While both the betta and the mollies are likely to eat some of the fry, a few are still likely to survive from each brood and your tank could easily get overpopulated.
To Prevent Overpopulation, Keep an All-Female Shoal of Mollies
Once again, your solution to this problem lies in your choice of male-female combination. An all-female shoal of mollies certainly won’t get pregnant again and again!
It should be noted, however, that even an all-female group of mollies might still give birth to a single brood of offspring, since they may have been impregnated in the store before you bought them. At least you know that rounds two and three won’t be following up anytime soon!
An all-male shoal on the other hand is definitely not recommended, since male mollies like to spar, and having no females around to mate with may only make frustrations mount even more!
What to Do if a Betta Fish is Chasing Your Mollies?
We’ve given several suggestions to reduce the likelihood of aggression between bettas and mollies. If you’ve tried everything and your betta is still harassing your mollies, it may be time to remove either him or your mollies from the tank.
If you have a separate tank, you could always re-house them there, or alternatively, offer them to a friend or a pet store.
Check out our recommendations for the best betta tank mates like snails, shrimps, Corydoras catfish, or Khuli loaches on our specially dedicated page here.
Can a Betta Kill a Molly Fish?
If you ignore all of the advice that’s given and don’t intervene in time, then yes! It’s possible in some grave instances that your betta could kill a molly.
This would be a tragic and easily avoidable occurrence though. Make sure you do your homework and are willing to be responsible for your fish before mixing these two species together!
Mollies and bettas may not be a match made in heaven, but they can become amicable tankmates if you take the time to get your tank set up right and look after them thoroughly.
It may be especially worthwhile considering our advice on male-female combinations of these two species, as well as purchasing a larger tank.
With proper preventative measures and a willingness to remedy potential problems, then you could have some success at keeping these highly attractive types of fish in the same tank together.
If, on the other hand, you’re looking for a safer bet, then snails, shrimps, or bottom-dwelling fish may make a more reliable choice.