What’s the difference between koi and goldfish? How can I tell them apart?

Koi and goldfish may look similar, but the two are actually two different species. Goldfish were developed by selectively breeding Prussian carp for color mutations. Today, the goldfish is now considered an entirely new species from the Prussian carp. Koi were selectively bred from the common carp over many years to bring out certain colors and patterns. However, koi are still considered common carp and not a species of its own.
There are many ways to tell the two apart, but the easiest way is to look for “barbels” or “whiskers” near the mouth. Koi will have these barbels on the lips, while goldfish will not. Also, goldfish tend to be much smaller and exhibit more variety in body shape than koi. Koi tend to have a common body shape and have a greater variety of color and pattern.