Can Goldfish and Mollies Live Together?

Can Goldfish and Mollies Live Together?

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Goldfish and mollies have in common their small sizes as fish, but their needs for growth and even survival can differ significantly. Both goldfish owners, and those new to domestic fish care, have asked if these species can coexist in the same tank.

It is not advisable to have goldfish and mollies in the same tank, mainly because the species require different water temperatures to thrive and even survive.

Goldfish are considered cold-water fish and thrive in waters with temperature ranging from 68 degrees Fahrenheit, up to 74 degrees. Mollies, known as a tropical fish, prefer much warmer climes, preferring water around the 78 degrees mark.

As you can see, if you drop them into the same bowl, you’ll make one species unhappy. This does not mean they absolutely cannot live together in the same environment. It’s just not recommended if your aim is to maintain healthy fish in the tank.

Note that while goldfish are considered “cold-water” fish, don’t just drop them into cold water. Note that degrees are nowhere near freezing. In fact, they might be considered “lukewarm water” fish.

Differences Between Goldfish and Mollies

Mollies are very small fish that rarely exceed 5.5 inches in length. They are generally much smaller than goldfish, and have much shorter lifespans. Healthy goldfish can live for 15 years or more and push a full foot in length! Mollies might last 5 years.

Many species of mollies over many years developed the ability to jump from fresh to saltwater, sometimes even living decent lengths of time in brackish water, like in beachside swamps. Many can survive in waters up to a salinity level of 80%. That’s very salty water!

Goldfish are known as a fresh-water fish, but some species can survive in water with a salinity level up to 17%. So mollies are much more versatile. In fact, some might even say it’s a hardy species, fending off rough environments. Goldfish? Not so much.

Mollies are the tropical fish with origins in Central and South America. They can be found in Mexico and in some southern U.S. states. So their reach on a global scale is rather limited.

Goldfish are native to far-east Asian countries like China and Korea, and have been found in what is called Eurasia ~ which encompasses all of Asia and Europe.

Over many, many years they were introduced and bred so they can be found in every U.S. state except Alaska; and in at least 50 countries. Goldfish are essentially global in reach. This may be because they are adept at a range of water temperatures, while mollies need warmed H20.

From a pet perspective, many species of mollies can be considered exotic ~ even some names like dalmation molly or lyretail molly as names sound exotic. (Though there are also the white molly, golden molly, and black molly). Not so much with goldfish, though some versions can be quite colorful.

Interestingly, both come in a variety of colors ~ even though a color is included in the goldfish name. Sure, the most common color of that fish is gold-ish, or a shiny orange; but it also has species with colors like a more solid orange, red, yellow, brown, blue-gray, and even black. Some have color combinations, like white with orange or red.

Other Reasons Not to Mix Goldfish and Mollies in the Same Tank

Aside from water temperature, there are two other good reasons not to mix these types of fish:

  1. Goldfish are known as big producers of waste. That is, they hit the restroom a lot. This can make the environment not so favorable for mollies.
  2. Mollies give birth to live baby mollies ~ which can become easy prey for omnivorous goldfish. (Goldfish produce offspring via release of eggs).
  3. Older, mature goldfish may become aggressive, but overall the species is considered quite peaceful (though it will eat smaller fish). Readers report that some mollies can get quite aggressive in the tank ~ even nipping at goldfish and causing exterior damage! ~ if a tank is too crowded, or if the mollies are all males.

There actually are many fish owners who believe goldfish belong only with goldfish, that they are some kind of solitary species on its own. However, there are plenty of reports of goldfish with other species in the same tank. Just don’t let the goldfish get too large with the ability to eat smaller fish!

Tips for Caring for Mollies

Mollies differ from goldfish in that they are strictly herbivores, relying on plants and algae for sustenance. They are attracted to algae in tanks and aquariums so they are helpful for keeping the water and glass clean.

(Too-clean aquariums with little algae can be supplemented by introduction of spirulina flakes, food made specially for mollies for commercial consumption; or, use very small pieces of boiled and chopped spinach.

Other than that, try to keep the water warm and around 78 degrees, don’t overfeed, and remember not to use tap water when swapping out the tank. Never fully replace fish tank water, by the way. Always leave about 40% of the old water, to give your fish time to acclimate to the new environment.

Also, do not dump water into a tank too fast while swapping water. Do it a little at a time, like drip some in, stop, they drip some more in. This also helps not to shock the little fellas.

It’s wise to introduce at least five molly fish into a tank at the same time, with at least one being a female.

If You Really Want to Try Mollies with Goldfish

As stated above, while it is not recommended, it is possible to have goldfish and mollies co inhabitants. Here are a few tips in case you wish to test it:

  • Monitor. Particularly, watch the water temperatures. Some say the only option is to keep the water relatively cold, like no warmer than 74 degrees to please the more-sensitive goldfish, and put the stress on the mollies. (Although they do have a stress-relief action, noted at the bottom here).
  • Clean. Goldfish are rather known as messy waste-producers, not so good for the long-term health of molly fish. Making sure the tank is at least 20 gallons would help; so would having an electric filter.
  • Numbers. Introduce enough mollies at the same time so they are not intimidated by the larger goldfish.
  • Plants. Or decorations, to give fish places to hide if intimidated or otherwise bothered.

Related Questions

Question: What happens when mollies are in waters with temperatures below 78 Fahrenheit?

Answer: They can survive in waters up to a few degrees cooler, but in cold water they can tend to develop neurological ailments due to stress. One ailment is commonly called the shimmies. This is when the fish rocks its body from side to side like a snake. Some say this is its version of the shivering of human beings ~ moving the body in an attempt to get warm.

Question: Why are they called mollies?

Answer: Mollies are named for the original scientific name of their genus, Mollienisia, as first classified in 1846. Since then the genus was renamed Poecilia, after the family name Poeciliidae.

Question: Which fish eat the most algae?

Answer: It’s almost impossible to measure, but we would say it’s probably black mollies.