Coldwater aquarium fish

Coldwater fish are comfortable below the tropical range, so an unheated tank at room temperature suits them. 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 in practice 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.

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 45 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 the schooling species in groups of six or more.

Goldfish need more room than the bowl suggests

A common goldfish is an 8 inch (20 cm) fish that wants at least 24 gallons (90 liters) and company of its own kind; the bowl tradition does not survive contact with those numbers. Native sunfish run bigger still: a pumpkinseed needs a 70 gallon (265 liter) tank and defends its territory. 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 paradise fish are comfortable down to around 61 to 64°F (16 to 18°C), which makes them 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 Chinese butterfly loach list temperatures from 61°F (16°C), the white cheek goby from 61°F (16°C), and 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, smooth stones and algae to graze, and they are the fish to build an unheated river tank around.

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 sunfish are a different proposition, hardy but marked aggressive and quick to own a tank. 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 and the Chinese high-fin banded shark are sold as small, striped, appealing fish and grow into 24 inch (60 cm) and 27 inch (68 cm) animals that list 264 and 528 gallons (1,000 and 2,000 liters). European perch, channel catfish and the mahseers run bigger still. 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, any fish on this page: White Cloud minnows, medaka, zebra danios, rosy barbs, paradise fish, hillstream loaches and the smaller goldfish. Check each profile's low end against the coldest your room actually 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), while the true cold fish, weather loaches and sunfish among them, 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), but a common goldfish grows to 8 inches (20 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, and most of the natives here are sold captive-bred for ponds anyway.

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