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.

Goldfish 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.”

Goldfish are a hardy aquatic species. They can deal with temperature fluctuations, changes in pH, cloudy water, and even low dissolved oxygen levels.

If released into the wild, goldfish can group up into what’s called a school. But they don’t need companions to be happy in captivity and are fine if kept separately in a tank.