Fish That Don’t Need a Heater

Peppered Cory

Do you have a freshwater aquarium that needs to be stocked up with fish but don’t want a heater? Don’t worry. You can have an amazing fish tank full of brightly colored fish, even if the water is cold. There are plenty of varieties of fish that enjoy swimming in cooler water.

The most common cold water species of fish that is found in fish tanks and ponds would be the goldfish or koi. But since those fish are not ideal for smaller tanks and bowls, they are not always a wise choice for beginner fish keepers. Keep in mind that many coldwater fish grow very large, making them suitable for larger fish tanks and outdoor ponds.

If you are planning on keeping fish that don’t need a heater indoors, you need to focus on options that are small to medium in size.

To help you find the right fish to stock your tank, we have come up with a long list of fish that don’t need a heater to survive. Let’s have a look.

Setting Up a Cold Water Tank

The main thing that we want to preface is that just because you have fish that don’t need a heater, it doesn’t mean they will survive without the correct water parameters. If you want a cold water tank, you are most likely going to need substrate, decorations, live plants, and a decent filter.

Some of the fish listed below can survive without a filter, too; but if you want to be a successful aquarist, it is best to invest in a filtration system.

Here are some tips to set up a great cold water tank where you fish can thrive:

  • Consider the kind of fish that you want. There are freshwater fish and marine ones. Since most freshwater tanks are warm, you are going to have to be on the lookout for freshwater fish that enjoy cold temperatures or can at least adapt to them.
  • Think about water volume. Some fish need less space, but all fish need room to swim. Once you know which fish you want, you can determine the minimum tank size.
  • Determine your budget. Can you afford a lot of live plants? How many fish can you afford to keep?
  • Think about where the aquarium is going to be placed. If you place the fish tank near a window, the water could heat up because of the sun. This could potentially create a poor environment for some fish.
  • Understand how to check and maintain water parameters. Even if the fish don’t require a heater, they do appreciate specific pH levels, flow rates, and so on. Do your research to know what your fish can tolerate. 

The Best Fish That Don’t Need a Heater

Comet Goldfish

comet goldfish

One of the best fish for an unheated aquarium is the comet goldfish, also called the comet-tailed goldfish. Like most goldfish, this type can get rather large (easily reaching 12 inches/25-30 centimeters) and requires plenty of space to swim. It will quickly outgrow a bowl or nano tank, so think about how much water it will need.

If your comet goldfish is well taken care of, it may survive for up to 14 years; most goldfish will live to around 7 years on average. Either way, you can expect to have your comet goldfish for many years.

You can keep one goldfish with tank mates around the same size (as it might eat anything smaller) or keep 3 comet-tailed goldfish in the same tank or pond.

White Cloud Mountain Minnows

white cloud mountain minnow

Hailing from China, the White Cloud Mountain Minnow is now almost absent from the waters of its homeland because of pollution.

It is a much smaller fish than a goldfish but is just as beautiful to look at. Coming in at around 1.5 inches (3.75 cm) long, the white cloud mountain minnow doesn’t need as much room as a goldfish and prefers to be kept in schools.

You need at least 5 fish to bring out the best of their personality. Other common variants of this fish include the Golden Cloud and Meteor minnow types.

Buenos Aires Tetra

Buenos Aires Tetra

Coming from the subtropical waters of South America is the Buenos Aires tetra. If you have ever been to Argentina, you may know how chilly the temperature can get during the winter. That makes this species of tetra ideal for cooler tanks.

Their physical appearance is pleasing—light brown scales intermingling with red. The caudal fins are marked with yellow and black, and there is a black diamond shape at the base of the tail.

Some people will even go as far to call the Buenos Aires tetra indestructible. These fish can be feisty when they are not kept in large groups but will be much more calm when in a school. Also, while you can keep them in a community tank with little issues, they tend to be ravenous when it comes to eating live plants.



There are plenty of fish found in North American waters that can survive without heated water, but there are few species available for freshwater tanks. One of the options, however, is known as the mosquitofish.

While these fish are usually sold as feeder fish for breeders, they are a great option for tanks. They are small, silvery, and look vaguely like a guppy.

Mosquitofish, as the name implies, can be kept in ponds to eliminate mosquito larvae. In the wild, they are found along the Atlantic coastline of the United States, including states like Maryland and Delaware.

Dragon Fish

Here is another fish that is not meant for small tanks, as it can grow to around 15 inches (37.5 cm) in length and will quickly devour critters, such as ghost shrimp and worms from the bottom of the tank.

The dragon fish is otherwise very peaceful. It also doesn’t see very well, so it can often miss food. You will need to ensure that it is getting enough food. Otherwise, the dragon fish is relatively easy to care for once it has plenty of room to swim and food to eat.

Balzani Cichlid

Balzani Cichlid

In the country of Uruguay, there are hot summers and freezing winters. That makes the fish there, like the balzani cichlid, incredibly prepared to deal with all kinds of water temperatures. The balzani cichlid comes from the rivers in Uruguay as well as the Parana River in Southern Brazil and Paraguay.

Balzani cichlids are known as eartheaters, meaning that, if given a sandy substrate, they will regularly scoop up mouthfuls of sand while searching for insects, crustaceans, and worms.

Male balzani cichlids can grow large, around 6 inches (15 cm), and have a more rounded head than the females. Males can also be very territorial. Because of this, it is smart to keep a single male balzani cichlid in a tank with mates or keep females together.

Peppered Cory

Peppered Cory

Are you looking for a bottom-feeder that can handle cool water? Look no farther than the peppered corydoras, a tiny catfish. The peppered cory comes from the same waters as the Buenos Aires tetra and balzani cichlid. It tends to like unheated waters so much that breeders are often seen dropping ice cubes into the tanks to stimulate breeding.

Dojo Loach

Dojo Loach

Did you know that the dojo loach, also known as the weather loach, can survive in both the glacial waters of Siberia and war tropical waters? Dojo loaches are remarkably cold resistant. The other name is derived from their habit of taking in huge gulps of air as the air pressure changes, usually before a storm is closing in.

They will enjoy water as cool as 50 degrees F (10 degrees C). Appearance-wise, the weather loach looks like an eel and has a gray, pink, or albino body. There are three barbels around its mouth.

Gold Barb

Gold Barb

The golden barb is also referred to as the Chinese barb and is a bright, shiny fish with golden scales. It can grow 2-3 inches (5-7.5 cm), so it needs a minimum of 10 gallons. Because of the stunning yellow, it is a popular fish for tanks that do not have a heater. They prefer a tank with a moderate current, but it is not necessary.

Bloodfin Tetra

Bloodfin Tetra

Similar to the Buenos Aires tetra in both appearance and size, the bloodfin tetra and the false bloodfin are two popular fish that can tolerate temperatures within the mid-60s (15-18 degrees C). The physical characteristics include thin, silvery bodies and red-colored fins. They do not have barbs.

Unlike the Buenos Aires variety, bloodfin tetra are much smaller (around 2-3 inches/5-7.5cm) and docile. They can be kept in groups of 5 or more and are very active round the surface. As long as you give them a variety of food to eat, they will be happy and healthy.

Pearl Danio

Similar to another danio on this list (see below), the pearl danio is a hardy and beginner-friendly fish that doesn’t need a heater. The pearl danio grows to about 2 inches (5 cm) in length. It is called “pearl” because of the pearlescent orange scales that separate it from other danio types. The forked tail and barbels are also characteristic of this tiny fish.

Pearl danios come from the waters of Sumatra and Thailand, but they can tolerate temperatures of around 60-65 degrees F (15-18 degrees C). If you are looking for a maintenance free addition to your tank, consider the eye-catching pearl danio.


red and blue guppies swimming

The guppy is one fish that is extremely hardy, friendly, and excellent for a number of tanks. It is why guppies are one of the most kept fish around—second in captivity—after goldfish.

That said, guppies are much easier to care for than goldfish, require less space, and are generally more forgiving if you mess up the water parameters. Guppies can also multiply by hundreds at a time, giving them the nickname the “one million fish.”

There are several kinds of guppies that will do well in a cold water tank without a heater, such as livebearers and fancy-tailed guppies. Most guppies are named for their tail color and shape. Usually females are larger, measuring around 1.0-2.5 (2.5-6.0 cm) in length; males are generally around 0.5-1.5 inches (1.27-3.80 cm).

Zebra Danio

Zebra Danio

Lastly, we have the zebra danio—an ever popular option. These are fish that do not need a heater or even much filtration in a tank. Native to the waters of South Asia, they are used to a range of temperatures and will tolerate water as low as 60 degrees F (15 degrees C). There are two species available: long-finned or leopard-spotted.

Typically, zebra danio grow to about 0.5-1.5 inches (1.27-3.80 cm) with little difference between males and females. Their bodies may have horizontal bluish stripes and gray or gold. Females sometimes have silver bellies while males do not.


Do you need to have a tank with a heater? Nope! There are fish that don’t need heaters available in pet stores near you. If you are searching for hardy fish that can survive without heated water, remember this list.

There are plenty of options for a variety of tanks. Just make sure that you are changing the water regularly and keeping the filter clean. Give your fish some sunlight, live plants, and some love, and you will have them for a long while.

Have a fish to add? Have questions about tanks without heaters? Got an experience to share? Leave a comment and let us know your thoughts!

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