Examples of cold-water fish that are seen in aquariums or ponds include goldfish and koi, along with lesser-known species including the pearl danio, the wimple and the weather loach. Salmon, mackerel, sardines, herring and tuna are among cold water fish that are used as food.
The goldfish is one of the earliest domesticated fish and one of the most common in aquariums. It is seen in various colors including red, brown and black, and is a member of the carp family along with the larger koi.
Other cold-water fish seen in aquariums include barbs. Bloodfin tetra and the Buenos Aires tetra are available in many pet shops and are easy to care for. Guppies are popular for aquariums and come in many varieties. Many cold-water fish are too large for aquariums.
Among food fish, cold-water varieties, including herring, salmon and tuna, are high in healthy omega-3 fats. Cold-water fish are one of only a few food sources of vitamin D. Wild-caught fish from salt water are the most nutritious. Tuna and mackerel, however, can have high mercury levels and should be avoided by women who are pregnant or breastfeeding and by the elderly and those who have compromised immune systems.