How to tell the difference between koi and goldfish is a fairly common question when people look at ponds. The are a lot of similarities between these fish but also numerous differences.
This video will explain many of these factors including size, colors, lifespan, cost and the amount of care that will go into keeping these pets.
One other telltale sign which I forgot to mention in the video is that Koi have little whiskers, also known as barbels. Where as goldfish do not.