The 10 Best Cold-Water Fish for Unheated Aquariums in 2027

Seriously Fish says the paradise fish can be maintained in an unheated aquarium in most cases and may even benefit from a cool winter period. It reaches 80 mm SL, suits a base of 80 x 30 cm for a pair, and is rated Moderate. Males are territorially aggressive, so Seriously Fish advises two or more females per male.

Seriously Fish calls the White Cloud Mountain minnow very peaceful and says that in many countries or well-insulated homes it is best kept without artificial heating year-round. It reaches 40 mm SL, is rated Easy and suits a 60 x 30 cm base. All the fish on sale are commercially bred, and the species is considered endangered in China.

Seriously Fish says the medaka, a ricefish from Japan, Korea, Taiwan and China, is most comfortable at 16-22 C and is best kept without artificial heating in many homes. It reaches 36 mm SL and a base of 45 x 30 cm is recommended for a group. It is peaceful but not an ideal addition to many communities.

Seriously Fish calls the golden barb hardy and generally very peaceful, an ideal resident of the community aquarium. It reaches 75 mm SL, suits a 90 x 30 cm base and is rated Easy. Seriously Fish suggests a mixed-sex group of at least 8-10 fish, with other schooling fish for security.

Seriously Fish calls the rosy barb generally considered one of the hardiest small cyprinids in the hobby and an excellent choice for newcomers. It reaches 100 mm SL, is rated Easy and suits a 100 x 30 cm base. It is generally peaceful and best kept in a group of at least 8-10.

Seriously Fish calls the pearl danio very peaceful indeed and an ideal resident of a well-furnished community tank. It reaches 55 mm SL, is rated Easy and suits a base of 90 x 30 cm in a 16-25 C range. It needs a tightly-fitting cover because danios are accomplished jumpers.

Seriously Fish says the giant danio comes from hill streams in northeastern India, Bangladesh and Nepal and prefers a tank set up like a flowing stream. It reaches 75 mm SL, suits a base of 120 x 45 cm and is rated Moderate. Its range is 16-26 C, and its constant activity can upset timid tankmates.

Seriously Fish calls the zebra danio peaceful, hardy and inexpensive, and says its recommended 18-25 C range means a heater may not always be required. It reaches 50 mm SL, suits a base of 90 x 30 cm and is rated Easy. Keep a group of at least 8-10.

Seriously Fish lists the Malabar danio at 18-25 C and 80 mm SL, rated Moderate because it needs a well-established tank and stable water. A base of 120 x 45 cm is the minimum considered, and it prefers a flowing-stream set-up. It needs a tight lid and weekly water changes of 30-50 percent.

Seriously Fish says the oriental weather loach, sold in the US as the dojo loach, is exceptionally hardy, can apparently tolerate 5-25 C, and should get 18-23 C for general care. It also says the species is established as an alien species around the globe and that its adult size of up to 280 mm should be considered prohibitive. LiveAquaria says dojo loaches are illegal to own and purchase in Illinois, Michigan, Minnesota and New York, and the US Fish and Wildlife Service says possession, trade or transport is regulated in at least seven states. Check your state rules before buying.