Coldwater fish

Coldwater fish, in the context of aquariums, refers to fish species that prefer cooler water temperatures than tropical fish, typically below 20 °C (68 °F). Some examples are koi and goldfish. These species tend to grow more slowly and live longer than fish that live in warmer waters, and are generally felt to be easier to keep.

Coldwater fish are fish such as goldfish, koi, and other members of the carp family that are able to survive in cold water temperatures. When kept in a household aquarium, they do not require a heater and are quite comfortable at around 60 °F (15 °C). These fish are also desirable choices for outdoor ponds and can stand temperatures down to 10 °C.

Note: The above contains a mix of true coldwater fish and sub-tropical fish that can survive and thrive at room temperature which ranges from 15 °C (59 °F) and to 30 °C (86 °F).

The term is also used to refer to fish species in the wild (such as lake trout, Arctic char, and Arctic grayling), that prefer colder waters.

Marine Aquarium Fish - http://www.oregonreef.com/sub_coldwater.htm

Freshwater Aquarium Fish - Practical Fishkeeping Magazine

Freshwater Pond Fish - An Essential Guide to Choosing Your Pond Fish and Aquatic Plants by Graham Quick and also http://www.pondexpert.co.uk/ChoosingTheRightFishForYourPond.html

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Wikipedia