Koi are actually a type of carp, and today they're some of the most expensive pet fish in the world. But why? Koi were originally raised in Japan in the 1700s when rice farmers first began ...

Koi aren't lightweights either; they typically tip the scales around 35 pounds (16 kg), and experts advise filling a pond with about 500 to 1,000 gallons (1,893 to 3,785 liters) of water per each ...