They also come with either a six, nine or twelve-year limited warranty that covers the tank and parts.
Twelve animals represent the Chinese zodiac which is based on a twelve-year cycle of birth.
Before the years were assigned an animal, the twelve-year lunar cycle was governed by the theory of the Twelve Earth Branches.
One animal is assigned for each year of the Chinese twelve-year cycle.
Below is a twelve-year progression of the Chinese calendar and the astrological animal signs for each.