When building a home aquarium and keeping fish, it’s important to consider what breeds of fish can peacefully live together, and also which cannot.
Two popular fish breeds that I often see people considering are mollies and goldfish. Both of these fish are incredibly popular fish as a breed, but can they actually live together?
In this article, I will look at the characteristics of both fish to see what their requirements are, and to see whether or not they can live together happily and peacefully (or if it will end up as a fishkeeping nightmare).
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Can Mollies Live With Goldfish
You may already have a small school of mollies or a few goldfish in your tank and as you look to make your tank more diverse, you might be wondering whether or not mollies and goldfish can live together?
Unfortunately, mollies and goldfish cannot live together as they are incompatible tankmates. The main reason being that mollies are tropical water fish and require warmer temperatures whereas goldfish are coldwater fish. Mollies are also semi-aggressive and will nip at the goldfish and compete for food.
Before digging deeper into the issue with keeping mollies and goldfish together, I’d recommend watching the video below for a quick summary of some of the issues that I’m about to cover.
Why Mollies and Goldfish Can’t Live Together
You’d be surprised to hear that there are quite a few reasons why mollies and goldfish can’t live together. When I say can’t, I don’t mean that it’s impossible and there will be some people that make it work.
What I mean by can’t is that they shouldn’t be kept together and the reasons below explain why:
Water Temperature
The first issue with trying to keep mollies and goldfish together in the same tank is that they have very different requirements in terms of water temperature. Mollies are tropical water fish whereas goldfish are coldwater fish.
The Aquarium Guide states that mollies need a consistent water temperature of 72-78 degrees Fahrenheit (though some are more comfortable with temperatures as high as 84 degrees), as this is similar to the temperatures they live in when in freshwater in the wild.
Goldfish, on the other hand, need a colder temperature of 68-74 degrees Fahrenheit.
As you can see, there is a small amount of crossover in the 72-74 degrees Fahrenheit range but this is towards the extreme ends of what both fish will be comfortable with. If mollies are subjected to colder temperatures then it will impact their immunity making them more prone to stress and illness.
Feeding
Goldfish are notoriously uncompetitive when it comes to feeding time and while they are significantly larger than mollies, you’d be surprised to hear that they will often miss out on food if there is competition.
By goldfish being uncompetitive, I mean they are generally slow and will not fight other fish for food. They may be large but this doesn’t mean that they get to feed first when in a tank with other breeds of fish, especially semi-aggressive fish.
Mollies are semi-aggressive fish. They are fast and are constantly swimming around looking for food sources including algae and fish flakes. Once food enters a tank and lands on the surface, you can guarantee that mollies will try to be first to this food.
This causes a big issue when trying to feed these fish in the same tank. As mollies tend to get to the food first, they run the risk of overfeeding. As goldfish are not very quick to get to feed, you run the risk of them being underfed.
The only way around this would be to feed your goldfish in specific areas of the tank that the mollies can’t get into (which is difficult because of their size) or feeding them directly with some long tweezers or a similar tool.
Tank Size
Mollies need at least a 20 gallon tank to give them enough room to swim around. Despite their relatively small size, they like to make use of a large tank and also require a lot of plants to feed on algae and also plenty of hiding spots.
These requirements seem reasonable when you only have mollies in the tank but what happens when you add a large (and messy) goldfish into the mix?
Goldfish are great fish to keep for beginners because they are relatively easy to care for and are hardy fish. They do, however, make quite a mess in the tank and therefore require a larger tank. Coincidentally, goldfish also require a 20 gallon tank.
Simple math shows that if a goldfish needs a minimum of a 20 gallon tank (just for themselves), and mollies need a 20 gallon tank, for both to live together you would need a very large tank.
Trying to make both fish live together in a small tank would not be suitable for either breed of fish and would cause multiple issues. A large tank would therefore be required before you even consider trying to keep these two breeds together.
Nipping
This point will vary depending on the breed of your goldfish but, in general, mollies tend to be fin/scale nippers and it’s not uncommon for them to nip at goldfish. I mentioned earlier that size doesn’t tend to matter as goldfish are not aggressive and therefore mollies will nip at them without retaliation.
This can lead to goldfish having damaged fins, lost scales, being uncomfortable in the tank, and becoming stressed. If goldfish were not such peaceful fish then this wouldn’t be an issue but their passive nature makes them an easy target for mollies to nip at.
This, therefore, is a good enough reason to mean that mollies and goldfish would not make good tankmates in the majority of cases.
How to Keep Mollies and Goldfish Together
If you still want to try and keep mollies and goldfish together then there are some crucial requirements that you’ll first need to satisfy.
- Tank size – A large task is an absolute necessity if you want to keep mollies and goldfish together. I’d recommend a tank that’s a minimum of 40 gallons and depending on the number of fish you want to keep this might need to be even larger. Make sure you provide plenty of plants, ornaments, and hiding places as well. Both breeds of fish like having places to hide so this also needs to be considered.
- Water temperature – This will be the most difficult to get right as the correct water temperature is one of the most important factors for proper fish care. If a fish is not in their ideal water condition, they’ll quickly become stressed and ill as a result. Mollies, as a result of breeding over the years, can now withstand slightly colder temperatures and still be comfortable. As I mentioned earlier, the crossover point between a molly and goldfish is a water temperature of 72-74 degrees Fahrenheit so this is the temperature you should look to use.
- Feeding – You’ll have no issue feeding your mollies. Mollies are always looking for food and like to nip at plants for algae alongside their usual feeding pattern. Both mollies and goldfish are omnivores and their diets are very similar but as discussed earlier, goldfish are not competitive eaters. If you want to keep goldfish and mollies together, you’ll need to feed them manually and ensure that both fish are getting the correct amount of food. Particular attention will need to be paid to the goldfish and you might need to try different tactics to ensure they get their food.
- Cleaning – Goldfish are notoriously messy fish in terms of pooping. Just keeping a goldfish on its own is time-consuming for some owners, goldfish might be easy to care for but that doesn’t mean they don’t need plenty of water changes to keep the tank clean. When you introduce them into a tank with other fish, it’s even more important to keep the water clean as this can cause the other fish illness or infection.
- Temperament – Some mollies can be semi-aggressive and are known to be fin nippers. When first introducing mollies and goldfish into the same tank you’ll need to watch them regularly to ensure the mollies are not being aggressive and nipping at the goldfish.
Final Thoughts
While it’s good to get some variation in your tank in terms of different fish breeds, it’s important to ensure these different breeds can not only live comfortably together but also that they can thrive.
Unfortunately, mollies and goldfish do not make good tankmates and I would advise against keeping them together if possible. Their requirements and personalities are too different and it would not be worth your time trying to make them compatible.
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