We’re always told that having an aquarium heater is an absolute must…and most of the time that is correct – but not always!
If fact, there are tons of fish that don’t require heaters at all.
In this guide, we will go over a few species of cold water fish that you can keep at home without the use of any heat source.
What are Cold Water Fish?
As the name suggests, “cold water fish” are fish that thrive in colder water temperatures. In fact, a lot of true cold water fish cannot tolerate the warm water that we generally keep tropical fish in.
For that reason, many species of cold water aquarium fish should be kept in species only tanks.
So why would someone keep a coldwater aquarium?
In general, cold water tanks tend to be cheaper (you don’t have to buy/use electricity for heaters) and less maintenance (you don’t really have to worry about maintaining water temperatures).
In addition, algae tends to have a harder time growing in cooler environments.
As long as you’re keeping your aquarium indoors, room temperate tend to work well for a lot of the fish species below.
Fancy goldfish are a selectively bred variety of the Prussian carp, the carp that both fancy and common goldfish come from.
Common goldfish are not good aquarium inhabitants, as they get too large and fast for aquariums under 150-180 gallons.
Fancy goldfish do not get as large and cannot move as fast as the common goldfish, so two can be comfortably housed in a 40 breeder. They are a wonderful fish to own, very interactive, and can thrive at most home temperatures.
Keeping them between 55° and 80° Fahrenheit will keep your fish happy. They can survive a wider range, between freezing and 90°, but you will notice behavioral changes and increased disease susceptibility, so it is better to keep them in their preferred range of temperatures.
They are a social animal, so they should be kept in groups or pairs.
Goldfish are not picky eaters, but they should be fed mostly vegetables and plant-based pellets, as too much animal protein will cause bloat.
Feeding blanched vegetables on a weekly basis is a good trick for keeping them healthy as well.
White Cloud Mountain Minnow
White cloud mountain minnows are a smaller species of schooling fish, reaching just over an inch and a half in length. They come in two main color varieties, their normal coloration and a “gold” coloration.
These fish are fast, so a 20-gallon tank is a good minimum for them to provide enough room. They can handle temperatures between 40° and 80° but prefer the same temperature range as goldfish.
However, they do not make great tank mates for goldfish, as there is always a chance that the goldfish will eat them, given their small size.
White cloud mountain minnows are an endearing little fish and a great addition to most tanks.
Their speed coupled with their shining and glittering scales adds that little something special to any tank they are in.
Rosy Red Minnow
Rosy red minnows are a selectively bred variant of the fathead minnow, which is gray and silver in the wild.
They can get a bit over two inches and don’t always swim in a schooling pattern, but you should buy at least six, as they are considered a social and schooling fish.
The Rosy red minnows have a massive temperature range, from freezing up to 100°, but they do prefer living between 50-85°.
For all fish listed, the higher the temperature, the faster their metabolism, which means the shorter the lifespan.
Rosy red minnows are also very hardy fish and this, coupled with their temperature tolerance, means that they are a great beginner fish.
Asian Stone Catfish
Asian stone catfish do not have as wide a temperature range as the rest of these fish, but they are incredibly unique and still thrive in unheated aquariums.
They prefer their temperature between 60° and 75° and do not survive a range much wider than that.
These fish are rather unique in their appearance and their small size and are one of the few catfish that can live their whole life in a 5-gallon aquarium.
That being said, a 10 gallon is better because they are a schooling fish, so you should keep at least three or six of these tiny, 1.5-inch fish together.
The dojo (or weather) loach is a commonly sold loach that has a thick, cylindrical body shape.
Their faces are quite adorable to those who like loaches and catfish, and they have short, stubby little fins. These loaches come in two main color varieties, one of which is gold, and the other which is a silver with black spots.
Dojo loaches need to be kept in schools of at least six and should be kept on sand substrate.
These fish often burrow, and if they attempt to burrow in gravel, they will injure and cut themselves.
Dojo loaches need large aquariums, at least 40 gallons, as they often reach between 6-10” in size and need a relatively large school. Temperatures between 60° and 80° are perfect for them.
The paradise fish is a beautiful species of gourami, reaching about four inches in length. The males have beautiful flowing fins and striking, bright coloration across their bodies.
The paradise fish can be aggressive at times, and very nippy, so tank mates should be chosen carefully. Give the paradise fish a good bit of space, at least 30 gallons, as they love to swim around and need the room.
They prefer temperatures between 60° and 85°, which should be perfect for an unheated aquarium.
The paradise fish is easy to feed and does work well in community aquariums when living with appropriate tank mates.
There are several different species of ricefish that qualify as cold-water fish, such as Daisy’s ricefish, but the Medaka is more tolerant of lower temperatures and more available.
This fish is often overlooked and not as available, but it is definitely a beauty and is fortunately becoming more popular and widespread.
If you want an outdoor pond with small fish, some rosy red minnows, white cloud mountain minnows, and medaka ricefish would be perfect.
This ricefish is capable of surviving temperatures down to 40 and upwards of 100, about 105, so they are great candidates for ponds.
Some have a lovely pale orange coloration, which contrasts beautifully with the white rim that sometimes appears on their fins.
The Odessa Barb is a very attractive schooling fish. It has black ringed scales, black spotted fins, and a bold red stripe down its middle.
Alone, they look stunning, but when schooling in a large group, they are breathtaking.
As a schooling fish, they need at least five other friends, and the effect of their school is a sight that should not be passed up.
They need to live in temperatures between 65 and 75 degrees and are great candidates for community tanks.
That being said, both barbs and tetras tend to nip other fish if their schools are too small, so if you have an issue with nipping, try increasing the size of their school.
Rosy barbs are best kept in relatively large tanks, 50 gallons and up, as they reach six inches in length and need a school of at least six.
These fish are impressive, in both their bold red and pink coloration, and in their size.
Just like the Odessa Barbs, they prefer a temperature range between 65 and 75 degrees Fahrenheit.
The rosy barbs also come in a long-finned form, which is quite interesting to see.
This fish looks best in a planted tank, as their red against the green plants is a great contrast for the tank.
Gold barbs are more similar to the Odessa Barbs in size, reaching about three inches. They also have similar patterning to the Odessa Barbs, as their golden scales also have black rings around the edges.
The gold barb prefers temperatures between 65 and 75 degrees and a twenty long or thirty-gallon tank is a good size to provide enough room for at least six gold barbs to swim around.
Just like the other barbs mentioned, they normally fit very well in community tanks, though they can be nippy.
There are several species of pygmy sunfish, all of which are quite gorgeous and colorful.
Most of them can be kept in tanks as small as 5 or 10 gallons. These fish are also often kept in ponds due to their temperature tolerance.
They tolerate temperatures from 40° to 80° and, depending on the species, they reach only one half or two inches in size.
The majority prefer temperatures from 60-75, which is perfect for unheated aquariums.
These species do best in species only tanks, as opposed to community aquariums, due to their small sizes, shyness, and occasional pickiness when it comes to food.
Bloodfin tetras are another gorgeous schooling fish and are great additions to community tanks 30 gallons and above.
They have shining silver bodies with striking blood red coloration on the fins, hence their name. Bloodfin tetras reach about two inches in length and need a school of at least six.
They are not picky eaters at all, which makes feeding them very easy in a community aquarium.
The reason that schooling fish need to be housed with others of their own kind is to prevent stress and increase security. Schooling fish will constantly be stressed unless they have enough members of their own kind to feel secure.
Most of them are relatively small in size compared to the fish they live around, so they are only safe in large numbers.
Platies are a very common pet fish and often sold as a starter fish.
They can reach 4 inches in length, so a 20 gallon is the best sized tank to start them out in. That being said, they often only reach their size potential in 55-gallon or larger tanks.
The Platy is a live bearing fish and should be kept in a ratio of two females per every one male. Females become pregnant and give live birth to 10-30 babies every 4 or so weeks, so without a population control in place, they may quickly overpopulate their tank.
However, they are often cannibalistic, so it is rare for more than a few babies to survive from each batch.
Platies can tolerate temperatures from 60-85, but prefer temperatures from 70 to 80, a bit higher than the other fish listed.
There are dozens of species of corydoras, several of which are cold water fish, but the panda cory is the most commonly available one that tolerates lower temperatures. They can survive a range from 65° to 80°.
Many people see this as an opportunity to keep them with goldfish, especially because they often reach 2-3 inches, which many view as too large for the goldfish to eat.
However, corydoras have several spikes and spines along their bodies, and when a fish attempts to eat them, they often get stuck in the fish’s throat.
In many unfortunate cases, this results in the death of both the goldfish and the cory.
Corydoras are schooling fish, and quite adorably active, so keeping them in groups of at least 6 really helps to bring out their personalities.
Mosquito fish look very similar to guppies, but tolerate temperatures down in the 40’s and up to the 80’s. They are not often kept in the aquarium trade and can be relatively nippy, but they are simply overlooked.
The main reason they are overlooked is because of how similar they are to guppies, but instead of presenting thousands of different colors and patterns, they are a bold gray.
However, you cannot keep guppies in an outdoor pond in most of the world, but mosquito fish are a much better candidate, especially because of their ability to keep local mosquito populations down.
Bristlenose plecos are a smaller species of plecostomus catfish that only reach 3-5 inches in size.
They are often sold as algae eaters, but they have an appetite that rivals that of a goldfish, and a massive bio load to fit.
Adding a pleco to a tank is a much larger responsibility than adding a small algae eater such as a nerite snail.
However, they are extremely popular due to their personalities and prehistoric looks. Even though they do little in terms of algae control, they are still a wonderful and beautiful fish to own.
The least killifish is not truly a killifish but is the smallest known livebearer.
However, these fish do not give birth the way a guppy or platy does, with 30 babies at a time, but instead they release only one fully developed fry every few days.
The least killifish tolerates temperatures from 65 to 80, which most houses can handle. Temperature variance throughout the year is not a worry in heater-less aquariums; you should only be concerned if the temperature frequently fluctuated more than 2 degrees an hour.
This is an incredibly small animal, ranging from only three quarters of an inch to an inch and a half in size.
They do very well in tanks as small as 5-gallons, as long as they are heavily planted, as this fish tends to be skittish.
Danios are very fast, slim little schooling fish that require a decent swimming area, with 20-gallons being a good starting place for most.
There are some exceptions, such as the Gold ring dnaio, which does fine in a 10-gallon, or the giant danio, which gets five inches long, and needs a much larger tank than a 20-gallon.
The leopard, zebra, and long-finned danios are readily available and extremely hardy fish. Danios prefer temperatures between 65 and 75 degrees but can survive temperatures from 60° to 80°.
One Sided Livebearer
This fish is rarely seen in the aquarium trade, despite being quite a beautiful livebearer. Their bodies are a light tan or silver with gray and black horizontal spotting across their bodies.
They reproduce relatively rapidly, similar to guppies and platies and other livebearers. The females have a gestation period of about 50-70 days and produce between 10 and 20 fry after the gestation period.
In addition, the parents may still predate on the fry, so you should separate the parents from the fry.
This little fish, that scarcely reaches more than an inch in size, is a true cold-water fish, meaning they will not survive at higher temperatures.
Their aquarium cannot reach temperatures over 73 degrees, but they thrive quite well down to 60 degrees, and can survive colder temperatures.
The empire gudgeon is a gorgeous fish, with a striking red and tan colored body. Their fins continue that bright red coloration, followed by a black band, then edged in a white band, which is an impressive and striking pattern.
They do well in aquariums from 65 to 90 degrees.
This is a type of fish that does require a lot of frozen food and possibly live food.
Most of these are wild caught fish, meaning they are accustomed to preying upon crustaceans and insects in the wild, so you must replicate this through frozen food, mainly brine shrimp, blood worms, daphnia, and mosquito larvae. Empire gudgeons are extremely interesting to watch and quite amazing to keep.
The galaxy rasbora, also known as the celestial pearl danio, is a beautiful small schooling fish that only reaches a size of one inch. They have a gray body speckled with white spots and occasionally have orange fins.
They do very well in planted takes, as long as they are at least 10-gallons.
In addition, they are schooling fish, they do need at least 5 friends with them, but since they are so small you can often fit 8 or 10 in your tank.
This fish does not do well at temperatures higher than 75 degrees Fahrenheit, and they prefer temperatures between 65 and 75 degrees.
While they can be quite shy, they’re not picky eaters and soon come out of their shells in community aquariums.
This fish has a very cute face that almost makes it look like it’s smiling, similar to most puffer fish. It has a tan body with the occasional horizontal black stripe across, coupled with several spots in the center of its body along that line.
Some of them will also appear orange in color.
This livebearer is not often seen in the aquarium hobby despite its relatively easy care and small size of 2 inches.
Thus far they’ve only been kept in species only tanks so their compatibility with other fish is not known.
They prefer temperatures between 65 and 73 degrees, with higher temperatures being extremely harmful to them.
The Amano shrimp is a relatively recent addition to the aquarium hobby, but since it’s addition, it has become very widespread.
This shrimp is a social animal and should be kept with at least 2 others of its own kind.
They are one of the best aquarium organisms for eating algae and they get approximately 2 or 3 inches long.
They’re very tolerant of temperature, and live comfortably between 60 and 80 degrees Fahrenheit, though they are most commonly kept at the higher end of their temperature range.
Amano shrimp are not meant to only eat algae and they do require some additional protein, so be sure to feed them some shrimp pellets or other relatively high protein foods.
Thai Micro Crab
The Thai Micro Crab is another animal that is purely meant for species only aquariums due to its small size which makes it extremely delicate.
This crab cannot be live with any fish as the crabs will be eaten, however it has been kept successfully with some smaller invertebrates such as cherry shrimp.
Their shells do not reach over half an inch in length and are often below this size.
Just like most invertebrates, they are more sensitive to ammonia, nitrite, and nitrate then fish are, and you should know your GH, KH, and TDS values before keeping them.
They also appreciate having leaf litter, as they can prey upon small infusoria that live within the leaves.
Although there are many different species of crayfish, a 40-gallon or 55-gallon tank should be large enough for the majority of them.
They are not considered a peaceful animal (with only a few exceptions) and they should not be kept with any fish that you are afraid to lose.
They are often kept with feeder fish as these are cheap and do not live long with the crayfish.
Ensure your water is hard enough to allow it to molt properly, otherwise it will have a bad molt and die.
They are not sensitive to temperature and most can be kept anywhere between 50 and 85 degrees Fahrenheit, without showing any behavioral changes.
Axolotls or neither a fish nor an invertebrate, but rather a salamander that never undergoes metamorphosis from its larval stage.
Essentially, all axolotls are babies, which makes sense considering their cute little faces.
Most of their diet should consist of worms, whether it is the bloodworm (which is not an actual worm) or earthworms.
They reach over a foot long, but due to their inactive nature, a 30-gallon or 40-gallon is a good size for them, with a 40 breeder being ideal.
Some websites often list a 10-gallon as being an appropriately sized tank for this animal. However, once it reaches its adult size, it will not have enough room to turn around, and it will take up more than 1/2 of the length of the tank, which is cruel.
They do not tolerate temperatures over 73 degrees and prefer to live between 60° and 70° but can tolerate colder water.