Although both goldfish and koi are descended from the crucian carp, koi have feeler barbels and generally grow longer than goldfish. Goldfish have bigger fins and a more compressed body shape, while koi are longer and more cylindrical in shape and proportion.
Goldfish come in many different varieties and assorted colors and can live for 25 years or more. Once a prized possession of nobility, goldfish are now commonly found in freshwater aquariums and ponds. It isn't recommended that goldfish be kept in a bowl, as it does require filtration to prevent ammonia build up and adequate room for swimming. A species of cypriniforme, a carp-type fish native to Asia, goldfish are a slightly less common carp species due to their lack of feeler barbels.
Considered to be fancier versions of the common carp, koi use their long barbels to dig for food. They come in vibrant metallic and red colors and have bodies which can grow to about 1 meter long. Generally requiring larger tanks or ponds than goldfish, koi can live for 60 years or more.
Both koi and goldfish can be easily tamed and make excellent pets, although koi are considered more intelligent and sociable than goldfish and even poke their heads out of the water to take food from their owners.