Goldfish
The goldfish ("Carassius auratus") is a freshwater fish in the family Cyprinidae of order Cypriniformes. It is one of the most commonly kept aquarium fish.
Common goldfish
Common goldfish can be kept in water gardens or outdoor ponds throughout the year. Outdoor ponds have similar care requirement as indoor tanks with some notable exceptions such as amount of sunlight, natural and artificial environment pollution (i.e. dead leaves, debris, runoff), algae, selection of pond mates (i.e. algae eaters, frogs, etc.). Outdoor ponds tend to become miniature aquatic ecosystems, attracting various animals and plants (see water gardens for more information). In hot climates, it is important that pond temperatures do not rise to dangerously high levels which will kill the fish. In the winter, fish may become sluggish and stop feeding. This does not mean they are sick, but rather that their metabolism has slowed. The pond must not freeze solid and there should be an open spot in the surface ice to allow oxygenation of water. The ice should also not be struck, as this sends shock waves of sound pressure through the water scaring the fish.