FishBaseHQ

2026-10-28 · 9 min read

Fish that don't need heaters

Unheated aquarium fish: white cloud mountain minnows, zebra danios, goldfish. Room temperature matters. Tropical tetras still want a heater.

“No heater” means the room stays in the species’ range, winter included. A 68°F apartment is not the same as a 55°F garage. Put a thermometer in the tank. Guessing is how you get 60°F surprises after the heat pump setback.

Tropical tetras, bettas, guppies, and angels still want a heater. The heater calculator exists because rooms get cold at night even when the listing said “room temp.”

Actually unheated (if the room is cool)

FishComfortable rangeTankCatch
White cloud mountain minnows~60–72°FSchool of 6+ in a 10–20They sulk at 78°F. Do not mix with discus.
Zebra daniosmid-60s and upSchool, they are fastThey will nip slow long-finned fish.
Common goldfishCoolPond or a very large tubUnheated is correct. A 10-gallon is not.
Fancy goldfishCool40+ per fish is the honest startHuge waste. Weekly big water changes.

Cherry shrimp tolerate a wider range than tetras, down into the mid-60s, but they are not a reason to skip stability. See cherry shrimp.

Weather loaches and white clouds are the usual “unheated community” pitch. Weather loaches get large and restless. Read the profile before you buy three for a 20.

Not unheated

Bettas, neons, cardinals, guppies, platies, mollies, angels, most gouramis. Sold as tropical because they are. A week of 68°F nights is how you get ich, not a hardy fish.

Do not mix white clouds with discus or rams. Compatibility will flag the temperature gap. That is the point.

If you skip the heater

  • Park the tank away from windows, exterior doors, and AC vents.
  • Use a thermometer you can read from the couch.
  • Pick fish whose profiles list a low end that matches your winter nights, not the afternoon high.
  • Goldfish still need filtration and water changes. Unheated is not unmaintained. Water change calculator.

If the room dips below the low end on the profile, buy the heater. Watts from the heater tool, sized for the delta between the coldest room temp and the target, not a “5 watts per gallon” slogan.

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