Thank the Chinese for today’s beloved aquarium mainstay, the goldfish. A type of carp, goldfish were domesticated nearly 2,000 years ago for use as ornamental fish in ponds and tanks. They were seen as a symbol of luck and fortune, and they could only be owned by members of the Song Dynasty.

The fish are now ubiquitous in bowls throughout homes, classrooms, and doctor’s offices. They even share a name with a cracker, fondly known as the “snack that smiles back.”

Don’t confuse goldfish with its oversized cousin koi, another type of domesticated carp. There’s a common misconception that koi are large goldfish, but they are distinct species.

Goldfish weren’t always, well, gold.

Prussian carp, from which goldfish were domesticated,