The Comet is more active than most other goldfish breeds. It is not unusual to see a Comet dashing back and forth in his tank, racing around in a playful manner. Due to the comet's hardy and active nature, and the relative ease in caring for them, they are the breed best suited to ponds and outdoor pools. They are often kept with koi in outdoor ponds. Comet goldfish have a natural life span of 7 to 14 years and may live even longer in optimum conditions.