Coldwater aquarium fish

Coldwater fish are comfortable below the tropical range, and most of them suit an unheated tank at room temperature. Darters, sticklebacks, the giant stone loach and several others top out at 64–70°F (18–21°C) and need a cool room or a chiller. Goldfish are the classic, but White Cloud minnows, weather loaches and paradise fish belong here too. Each profile lists the temperature range and tank size a species needs.

Tank size: 5–5,283 gal; 5 gal (20 L) to 5,283 gal (20,000 L); half the list needs 25 gal (95 L) or more
Temperature: 61–75°F; 16–24°C, most of the list
pH: 6.5–7.5; Most of the list
Difficulty: 48 easy; 119 medium · 36 difficult
Temperament: 80 peaceful; 102 mostly peaceful · 21 aggressive

191 species and 32 varieties

What counts as coldwater

Coldwater covers fish that are comfortable at or below 64°F (18°C), which for most of them means an unheated tank at room temperature. That is the appeal: one less piece of equipment, one less thing to fail. And the category is much bigger than goldfish; small schooling minnows, North American natives and a few oddballs all live happily without a heater. The darters, sticklebacks and other true cold fish find room temperature too warm, so their tank has to stay cool.

Good coldwater fish for smaller tanks

White Cloud Mountain minnows and medaka are the easiest starting points: peaceful schooling fish around an inch and a half long, happy from about 10 gallons (35 to 38 liters). Rainbow shiners bring real color to an unheated 20 gallon, Everglades pygmy sunfish fit tanks as small as 8 gallons (30 liters), and fathead minnows are close to indestructible. Keep White Cloud minnows and medaka in groups of six or more, and rainbow shiners in groups of eight or more.

Goldfish need more room than the bowl suggests

A common goldfish reaches 9.8 inches (25 cm), and its profile lists 50 gallons (190 liters) for one adult. It wants company of its own kind, so a pair or group needs more room. No bowl comes close to those numbers. The pumpkinseed and bluegill sunfish need a 70 gallon (265 liter) tank and defend their territory. The banded, blackbanded and Everglades pygmy sunfish stay small. If you are not sure what fits, the stocking calculator will tell you before the fish is in the bag.

Subtropical, not cold

Most of the fish on this page are not from cold water at all. Zebra danios, rosy and Odessa barbs, pearl danios and round-tail paradise fish are comfortable down to around 61 to 64°F (16 to 18°C). They are fine in a heated house without a heater and wrong for an unheated garage or porch. The profile lists the full range for each species, and the range matters more than the label. A living room at 68°F (20°C) and a shed at 50°F (10°C) are different tanks.

Cool, fast water

Hillstream loaches, the Rhinogobius gobies and the doctor fish come from streams that run cool and hard. The butterfly loach and the white-cheek goby list temperatures from 61°F (16°C), and the Chinese butterfly loach from 64°F (18°C). The doctor fish tops out at 68°F (20°C), so a tropical tank is too warm for all of them. They want flow, oxygen and smooth stones, and they are the fish to build an unheated river tank around. The hillstream loaches and the doctor fish graze algae. The Rhinogobius gobies and the Asian stone catfish eat small live and frozen foods instead.

Natives and the pond crossover

The sunfish, weather loach, crucian carp, bitterlings and shiners are pond fish that happen to fit an aquarium. A weather loach reaches 11 inches (28 cm) and lists a 55 gallon (210 liter) tank, but it is as hardy as its name and lives happily at 50°F (10°C). The pumpkinseed and bluegill sunfish are hardy but marked aggressive and quick to own a tank. The banded sunfish is marked mostly peaceful, and the blackbanded and Everglades pygmy sunfish are marked peaceful. If you are tempted to collect native fish yourself, check the rules where you live first, since many places restrict it.

The coldwater giants

Koi are sold as small, appealing fish, and the Chinese high-fin banded shark as a small, striped one. They grow into 23.6 inch (60 cm) and 26.8 inch (68 cm) animals that list 264 and 528 gallons (1,000 and 2,000 liters). Channel catfish and the Tor and Deccan mahseers grow longer still. The European perch stays at 19.7 inches (50 cm) for 119 gallons (450 liters). These are pond fish, and their profiles say so.

By the numbers

Smallest

Largest

Easiest to keep

Most peaceful

Fits a 20 gallon tank

Fits a 30 gallon tank

FAQ

Common questions

What fish can live in an unheated aquarium?

In a normal house, most fish on this page: White Cloud minnows, medaka, zebra danios, rosy barbs, paradise fish, hillstream loaches and the smaller goldfish. The darters, sticklebacks, giant stone loach, doctor fish and several others top out at 64 to 70°F (18 to 21°C). A living room in summer can be too warm for them. Check each profile's range against both the coldest and the warmest your room gets.

What temperature counts as coldwater?

This list takes fish that are comfortable at or below 64°F (18°C). Many of them are subtropical and also happy at 75°F (24°C). The weather loach and the pumpkinseed, bluegill and blackbanded sunfish are true cold fish that live at 50°F (10°C) or lower.

Are White Cloud minnows coldwater fish?

Yes. The profile lists 57 to 72°F (14 to 22°C), so they suit an unheated tank in most homes and dislike a heated tropical one.

Can goldfish live with tropical fish?

The temperatures overlap around 72 to 74°F (22 to 23°C). A common goldfish grows to 9.8 inches (25 cm), eats anything that fits and fouls the water. Keep goldfish with goldfish.

Do coldwater fish need a heater in winter?

Only if the room drops below a species' low end. A zebra danio lists 64°F (18°C) and a White Cloud 57°F (14°C), so a heated house is fine for both; an unheated sunroom in January may not be.

Can I keep fish I catch from a pond or stream?

Check the law where you live first, since many places restrict collecting. Wild fish also carry parasites and settle poorly. The pond natives here, such as the fathead minnow, bluegill and channel catfish, are sold captive-bred anyway.

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