Far from being an innocuous domestic animal, a goldfish freed in fresh water is an invasive species, an organism that is introduced to an environment, can quickly reproduce, outcompete native species and destroy a habitat. And even though they get less attention than invasive organisms such as Asian carp or zebra mussels, goldfish appear to be a growing problem in bodies of water across the United States and around the world, triggering warnings from government officials in Virginia, Washington state, Australia, Canada and elsewhere.

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