About a thousand years ago, people in China discovered a unique color change in an ordinary carp. Instead of the usual brown-grey color, some fish developed a striking orange or red hue. These colorful carp were selectively bred, and this gave rise to the goldfish as we know it today. In the past, these fish were only allowed to be kept in the ponds of palaces and temples. They were rare and considered a luxury.

Today, the goldfish is one of the most well-known pets in the world. What was once a rarity is now a fish you can find in almost any pet store.

The skeleton of a goldfish is quite remarkable. It consists of more than 1,500 tiny bones—far more than a human has! Like many other fish, a goldfish never truly stops growing. If it lives in a small aquarium, it stays small. But if it’s placed in a large pond, it can grow into a sizeable fish.

Because fish live in water, they are supported by buoyant force. This means their skeleton doesn’t need to carry their weight the same way land animals’ skeletons do. As a result, they can grow larger without becoming “too heavy.” And that’s useful, because a larger fish can produce more eggs and has a greater chance of reproducing successfully.