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.
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:
They can live in a broad range of temperatures, with or without a heater, and they tend to prefer pH levels above 7.0. Mix them with live plants and other fish on this list, and you’re sure to fall in love with them!
Variatus platies come in a huge variety of colors and patterns and are very fun to breed.
This nano fish is quite popular in the aquascaping world because its golden spots and red-orange fins make it look like a tiny brook trout. It can tolerate pH of 6.8 to 8.0, moderate water hardness, and of course cooler waters. Also known as the galaxy rasbora, CPD, or Danio margaritatus, it has the reputation of being a little shy. However, given the right environment, you can often find the males circling each other in a dance off competition. Keep them in a school of six or more, and you’ll have a stunning display for your planted tank.
Celestial pearl danios look stunning in a planted tank and are often used by aquascapers to highlight their designs.
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 torpedo-shaped fish grow to 3 to 3.5 inches long and can be kept with other peaceful fish that enjoy similar water parameters. You should keep them in a school of six or more, which can be difficult since they’re a bit pricey and hard to source. However, if you have the funds and can wait a year for them to mature, you’ll be rewarded with the best colored fish you’ve ever seen.
This United States native fish is hard to find but well-worth the cost because of their unusual purple and pink coloration.
Need an algae eater for your unheated tank? Look no further. The hillstream loach (Sewellia lineolata) not only does an amazing job of munching on brown diatoms and green algae, but it also looks fairly unusual, like a miniature alien stingray sucking on the side of your glass. There are several types of similar loaches, such as the butterfly loach and Chinese hillstream loach, and most of them tend to enjoy cooler waters and pH from about 6.6 to 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. If you feed them well, you may see some breeding behavior, and baby aliens will start popping up all over the place.
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.
Poecilia wingei is like a smaller version of its famous cousin, the guppy, because it also has been bred to display many unique colors and fin shapes. 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. Plus, they’re quite peaceful and mix well with many of the fish on this list. To breed them, just set up a 10-gallon tank with approximately two males and four females. Fill the aquarium with live plants and lots of hiding spots, and soon you have a factory of life, bursting at the seams with fish babies.
Endler’s livebearers are very prolific and will easily breed in a planted aquarium with plenty of cover.
This killifish (Epiplatys annulatus) is another coldwater nano fish that can be kept in a community tank with other small species. They have striking blue eyes, their bodies are marked with wide vertical bands, and the males possess a tail that looks like a rocket flame (hence their other nickname “rocket killifish”). 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 prefer a pH of 6.5 to 7.8 with moderate water hardness, and they will readily 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.
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. Start with 10 to 20 shrimp for a 10-gallon aquarium, make sure they have enough calcium and minerals in their water, and soon you’ll be overrun with beautiful 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.
Looking for something a little bigger? Consider the dojo loach (also known as the weather loach or Misgurnus anguillicaudatus). This hot dog-sized fish can reach 10 to 12 inches long and therefore should not be kept with smaller species on this list, such as the celestial pearl danio or cherry shrimp. Instead, try the variatus platy, barbs, and other medium-sized fish that won’t be seen as food. Dojo loaches display many fun behaviors, such as scavenging for food with their whisker-covered mouths or burrowing into the gravel. They’re fairly cheap for their size and make a great addition to any larger-sized, coldwater aquarium.
Dojo loaches are often found in goldfish tanks because of their peaceful temperament and matching preference for cooler water.
Many barbs are great in cooler waters but often have the reputation for being fin nippers, so keep them in groups of six or more to minimize their aggression. The rosy barb (Pethia conchonius) comes in many varieties, such as normal, neon, and long-finned types. They are very quick swimmers but relatively peaceful, so you can keep them with other similarly sized community fish. The gold barb (Barbodes semifasciolatus) is a little more aggressive than the rosy barb, so they would do well with other barb species and dojo loaches. Both species grow to approximately three inches or more, should be kept in a 29-gallon or larger tank, and are quite entertaining to feed because of their hearty appetites.
Barbs are very fast swimmers and should be kept in a school of six or more to lessen any aggression.
Tanichthys albonubes is often sold as a feeder fish at pet stores, but they make great beginner pets because of their resilient ability to survive in almost any tank size and temperature (as long as it’s not too hot). 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. Get a group of 10 to 12 fish, breed them for fun, and enjoy their simplistic beauty.
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!