The goldfish is probably the most commonly kept fish in the world mainly due to its versatile nature in that it can be housed outside in ponds and indoors in aquaria. Goldfish originated from green carp and the classical golden colour was selectively bred. The goldfish may grow as large as 8in / 20 cm long in appropriate pond conditions. Fancy goldfish are usually kept as aquarium pets.These tend to have a fatter body shape and there are various types such as the moor, all black, the pearlscale and the orfe.
These are ornamental carp growing to a possible 3 ft long. Koi is an abbreviated form of their proer name “nishikigoi” Koi come in various colours from the self colours such as the ogon through to the kohaku or patterned varieties.Some koi exchange hands at very high prices. They have a high output of waste and tend to benefit from a pond filtration system.