The Goldfish of today originates from wild Asian carps, and all the different Goldfish variations are considered to be the same species: Carassius auratus auratus. The Goldfish was one of the first fish species kept in ponds by man. In China, wild caught carps were kept in outdoor ponds as ornamental fishes and selectively bred until the eventually turned into the first type of goldfish.
The ancestor of our modern goldfish is believed to be the Crucian Carp, Carassius carassius. You can find a wide range of different goldfish types, commonly divided into four main groups. The first group consists of the so called "Ce goldfish" or "Grass goldfish", the second group contains the fancy "Wen goldfish", the third group is where you find "Dragon Eye goldfish" with large and protruding eyes, and the fourth group is made up by the "Egg goldfish" that lacks a dorsal fin. Keeping goldfish in ponds is still very popular, but goldfish are also kept in aquariums. Some of the fancy goldfishes have anatomical features that make life in pond risky for them. They might for instance have a hard time catching food since their eyes are deformed.
When you keep goldfish in an aquarium, it is easier for you to make sure that the fish really eats. Ce goldfish / Grass goldfish In this group, you will find the original type of goldfish. They are quite similar to their wild ancestors and do not have any fancy features. One of the biggest differences between a wild Crucian Carp and a Goldfish from this group is the coloration.
Wild carps need a camouflaging coloration to survive, and mutations that cause unusual color variations are not common since those fishes rapidly become eaten. The early Chinese carp keepers appreciated the rare color mutations, and used these fishes for selective breeding. In the protected pond, the carps did not need to stay camouflaged. The modern goldfish can therefore be obtained in several color variations that would not be successful in the wild, including orange, lemon yellow, white, black and naturally golden.
Wen goldfish Eventually, the breeders managed to produce goldfish with long and flowing tails. Just like the mutated color variations described above, a long and flowing tail would be a problem for the wild carp, but in a protected pond the tail configuration didn't really matter. One example of a popular Wen goldfish is the aptly named Fantail goldfish. This fish is decorated with a dual-lobed tail that can grow up to 3 inches (7.6 centimeters) in length. A Wen goldfish is always equipped with a fancy tail and a dorsal fin.
Dragon Eye goldfish A Dragon Eye goldfish has eyes that protrude from its head. Two examples of popular Dragon Eye goldfishes are the Telescope Eye goldfish and the Bubble Eye goldfish. Egg goldfish Unlike the other forms of goldfish, the Egg goldfish is without dorsal fin. The Japanese Ranchu goldfish is one example of a commonly kept Egg goldfish. Sometimes a Bubble Eye goldfish will have no dorsal fin, and thereby be considered an Egg goldfish rather than a Dragon Eye goldfish.
Allen Jesson writes for several sites including http://www.seapets.co.uk, the UK's leading retailer of aquariums and fish tanks and http://www.saltwaterfreshwateraquarium.com, an excellent information resource for any owner of a salt water or fresh water aquarium.