The difference between koi and goldfish

Fancy goldfish will have to be brought inside over the winter. Koi will survive cold climates as long as the pond is at least two feet deep.

Whichever fish you choose, plan to have them around for awhile.

"Well the average goldfish that doesn't succumb to predators or illness is going to live 10 or 20 years, and the oldest goldfish on record was 43 years old," Rhudy says. "The oldest koi ever was over 200 years old, and an average koi may live 50 years."

When koi get old, they get big, growing to about three-feet long. Goldfish grow according to their environment, and will max out around a foot. If you truly can't decide, it's okay to mix and match. A lot of people have both species swimming around the pond without any problems.

Learn more:

Creating a koi pond: Here are some tips for building a beautiful backyard pond that koi or goldfish will love to call home.

Winter koi fish care: Learn how to take care of your koi when temperatures drop.