Goldfish, the Most Popular Pond Fish
Despite the illustrious honor of being a carnival prize or swallowed on a dare, Goldfish ( Carassius auratus) are the most popular choice of fish for a water garden. These fish are well suited for almost any pond size. The unfortunate reputation that follows goldfish is that of the fish in a bowl that dies in 2 days. Even in a small bowl (although not recommended because of limited surface area) goldfish, if cared for, can live many years.
Goldfish can be found in a number of varieties and colors. Through selective breeding over the centuries there are now many classified varieties of goldfish. The list can extend into hundreds of individual varieties, below are some of the most common.
Comet - The comet is generally the most common of pond goldfish. It has a long slender body. This is often the typical orange colored goldfish but can also be all white or white and red (known as sarassa).
Shubunkin - The Shubunkin has an identical body shape to the Comet. The difference is in the coloration. Shubunkins should have a base color of light blue, which is covered with patterns of darker blue, red, brown, white, or black.
Fantail - Another common pond fish is the Fantail. Fantails are shorter and more plump than comets. Their caudal fin (tail) is split giving them the fantail name. Basic Fantails can be found in any goldfish colors (calico, sarassa, etc.).
Black Moor - The Black Moor has the body of a fantail. As the name would imply this fish is solid black in color. Its most distinguishing characteristic is the bulging of the eyes.
Ryukin - Ryukins are very similar to the basic fantail. The primary difference is in the slope of the back. The Ryukin has a sharp slope between the head and the dorsal fin.
Oranda - Orandas are also of fantail shape. Their distinguishing feature is the headgrowth. The headgrowth is known as the hood and has the appearance of being covered with warts. 
Lionhead - The Lionhead is similar to the oranda in that it has both the fantail shape and headgrowth. The difference in this fish is that it completely lacks a dorsal fin.
Ranchu - Often confused with the lionhead the difference lies only where the body meets the caudal fins. The lionhead body extends straight out toward the caudal fin, while the Ranchu body drops off sharply from the top of the back to the caudal fins.
Bubble-Eye - The bubble-eye also has a shape similar to a fantail. The distinguishing factor of this interesting fish are the liquid-filled sacs that balloon out from below the eye sockets. The eyes of the bubble-eye are also pointed upward.
Pearlscale - The Pearlscale is also shaped like the common fantail. This fish gets its name from the dome-shaped scales that cover the body. The raised parts of the scale are brighter and have a pearly appearance.