When some owners of goldfish no longer want their pets, they dump them into local streams. But a new study found that releasing goldfish into the wild is a very bad idea.
Scientists in Australia tracked down pet goldfish that had been released into the country’s Vasse River. They found that the fish have become an invasive species—a non-native organism that harms local plants and animals. In the wild, the fish can grow to massive sizes—up to 41 centimeters (16 inches) long! Without natural predators, they reproduce quickly, gobble up plants, and spread diseases to native fish.
Goldfish invasions have also been reported in North American waters in the past few years. Ecologist David Morgan, who worked on the study, has advice for owners of unwanted goldfish: “Return them to the pet store.”