Selective breeding over many centuries has produced goldfish with many color variations and body types. The more extreme fancy goldfish variations are less hardy than their original wild ancestors .
Goldfish are divided into two basic groups, the flat body type and the egg-shaped body type.
The flat body type goldfish are among the hardiest of all the goldfish varieties. They are very good swimmers and their bodies are streamlined. In a community tank, they can easily compete for food. As a result they are extremely easy to care for and tend to make good pets for beginner fishkeepers. Goldfish in this category include the common goldfish, comet, shubunkin, wakin, and jikin goldfish.
The egg-shaped or round body type goldfish, as the name suggests, look like an egg with fins. Some varieties within this group lack dorsal fins, such as the ranchu and lionhead goldfish. These goldfish without the dorsal fins generally do not swim very well and cannot effectively compete for food when placed in a tank with goldfish that do have the dorsal fins. This is an important consideration to think about when selecting a goldfish.