10 Best Coldwater Fish That Don’t Need a Heater

Most freshwater pet fish require an aquarium heater because they’re used to tropical temperatures, but did you know there’s a whole class of coldwater fish that are perfectly fine at room temperature? Goldfish are the most well-known coldwater fish in the aquarium hobby, so in this article, we’re going to cover 10 more cool species that can live without a heater.

1. Sunset Variatus Platy

We have a special place in our hearts for livebearers (or fish that bear live young) because of how readily they make baby fish, but over the years, the sunset variatus platy (Xiphophorus variatus) has become one of our favorites. They combine all the things you would want in a perfect fish:

You can find them in many colors and patterns.

They can survive in all temperatures. You’ll fall in love with them when you mix them with other fish and live plants.

Variatus platies can be bred in a variety of colors and patterns.

2. Celestial Pearl Danio

Because of its tiny size and bright red-orange fins, this nano fish is very popular in aquascaping. It can tolerate pH ranges from 6.8 to 8.8, moderate water hardness, and cooler waters. It is also known by the Danio margaritatus, CPD or galaxy rasbora. The males can dance off each other if they are in the right environment. If you keep them in a group of six or more, they will make a spectacular display for your planted tank.

Celestial danios are stunning in a plant tank and are often used as accents by aquascapers.

3. Rainbow Shiner

As a native of the United States, the rainbow shiner (or Notropis chrosomus) is definitely used to cooler waters and is known for its brilliant purple and pink spangling, especially during mating season. These fish are torpedo-shaped and can grow up to 3 to 3.5 inches in length. They can be kept with peaceful fish that have similar water conditions. It is best to keep them in a small school of six or greater, as they can be expensive and difficultly source. You’ll get the best-colored fish if you have the finances and can wait one year for them mature.

This native fish to the United States is difficult to find, but it’s well-worth it because of its unusual pink and purple coloration.

4. Hillstream Loach

Do you need an algae eater to heat your tank? Look no further. The hillstream loach (Sewellia ligneolata), not only does an incredible job at eating brown diatoms, green algae, but also looks quite unusual, looking like a tiny alien stingray sucking on your glass. There are many types of similar loaches such as the Chinese hillstream loach and the butterfly loach. They prefer cooler water and pH levels between 6.6 and 7.8. Besides snacking on algae, hillstream loaches love to eat Repashy gel food, good quality wafers, and other foods that sink to the bottom of the aquarium. You may notice some breeding behavior if you feed them properly, and you will see baby aliens popping up all around the aquarium.

Hillstream loaches can be a little aggressive with one another, so either get one loach by itself or at least three in a group to spread out any territorial or breeding behavior.

5. Endler’s Livebearer

Poecilia wingsei is a smaller version its famous cousin, guppy. It has also been bred to have unique fin shapes and colors. However, if you get the original, wild-type Endler’s livebearer, they are very hardy and can live at room temperature with a wide range of pH from 6.5 to 8.5. They’re peaceful and can be mixed with most of the fish on this page. A 10-gallon tank can be used to breed them. It should contain approximately two males as well as four females. The aquarium should be filled with live plants. There should also be plenty of hiding places. Soon, you’ll have a factory full of fish babies.

Endler’s livebearers are very prolific and will easily breed in a planted aquarium with plenty of cover.

6. Clown Killifish

This killifish (Epiplatys annulatus) is another coldwater nano fish that can be kept in a community tank with other small species. Their striking blue eyes are accentuated by their vertical markings and their tails resemble rocket flames, which is why they are called “rocketkillifish”. Like many killifish, they tend to swim at the top of the tank, so make sure your aquarium has a tight-fitting lid to prevent them from jumping out. Clown killifish like a pH between 6.5 and 7.8 with moderate water hardness. They will lay eggs in floating plants, or a spawning mop.

Unlike some killifish, clown killifish are not an annual species and can live about three years or more if well cared for.

7. Cherry Shrimp

Neocaridina davidi are very popular among fish keepers because of their bright, Skittles-like colors, fondness for eating algae and leftover fish food, and ease of breeding (even outside in cold weather). You can easily purchase them at your local fish store or aquarium society auction, and sometimes even major pet store chains will carry them. For a 10 gallon aquarium, you can start with 10-20 shrimp. Make sure that they have enough calcium and other minerals. Soon, your tank will be filled with dwarf shrimp. For more information, check out our full care guide here.

Neocaridina shrimp were originally brownish-gray in appearance, but now they’ve been bred into many colors, such as red, yellow, blue, orange, green, and black.

8. Dojo Loach

Are you looking for something larger? The dojo loach, also known as the Misgurnus Anguillicaudatus or the weather loach, is a good choice. The hot-dog-sized fish can reach 10-12 inches in length and should not be kept alongside smaller species such as the celestial Pearl danio or cherry shrimp. You can instead try varitus platy, barbs and other medium-sized fish that aren’t considered food. Dojo loaches are known for their playful behaviors such as digging into the gravel or scouring for food with their whisker-covered faces. They’re fairly cheap for their size and make a great addition to any larger-sized, coldwater aquarium.

Dojo loaches often find their way into goldfish tanks thanks to their tranquil temperament and preference for cool water.

9. Barbs

Although barbs can be great in cooler water, they are often known for their aggressive nature. Keep them in groups of six to eight to reduce aggression. There are many types of the rosy barb (Pethia Conchonius), including neon, long-finned, and normal. They are very quick swimmers but relatively peaceful, so you can keep them with other similarly sized community fish. Barbodes semifasciolatus (the gold barb) is more aggressive than rosy barbs. This species would work well with other barbs and dojo loaches. They can grow up to three inches and should be kept in a tank of 29 gallons or more. Their large appetites make them quite entertaining to feed.

Barbs swim fast and should be kept in a group of six or more to minimize aggression.

10. White Cloud Mountain Minnow

Tanichthys albonubes are often sold at pet shops as a feeder fish. However, they are great for beginners because of their resilience and ability to survive in any size tank. Sometimes known as “the poor man’s neon tetras” because of their inexpensive price, nowadays these minnows come in many strains, such as albino, golden, and long-finned. You can get a group of 10-12 fish and breed them for fun.

Many people breed these hardy minnows outside in large plastic tubs during the warmer summer season.

If you enjoy articles like this, check out our Top 10 lists for more fish and plant stocking ideas!