Koi are, without a doubt, the staple fish of the pond hobby. The history of koi dates back to 400AD with the domestication of the common carp, though proper modern koi were first developed in Japan in the 1800's through selective breeding of naturally occurring color mutations. Koi come in countless colors and varieties, and new ones are being created all the time, some costing thousands of dollars.
Koi grow up to 3' long, and they grow rapidly. As such, it's recommended to provide them with an adequately sized pond of 1000 gallons or more. Koi are very adaptable, and can withstand temperatures as high as 90 in the summer to as low as 34 in the winter. In areas with harsh winters, care should be taken to ensure part of the pond goes below the frost line so that they have somewhere to go in a hard, sustained freeze.
Koi will thrive on any commercial koi pellet food blend Such as Koi Crunchies.