angelfish
Image: Courtesy of the U.S.G.S.

You thought that an aquarium and its exotic inhabitants would bring you hours of delight and relaxation. Instead maintaining it seems like a full-time job. Flush the fish? Too cruel. Probably better to release them in the nearest body of water and let them swim free, right? Wrong. According to the U.S. Geological Survey, dumping those creatures is about the worst thing you can do, both for them and for the ecosystem.

In a non-native habitat, fish become susceptible to parasites, diseases and predators that they are not equipped to fend off. At the same time, they may prey on or compete with the native fish, or even infect them with their parasites and diseases. Former pets can thus quickly become formidable pests. (Some aquarium speciesfreshwater stingrays and piranhas, for examplecan also pose a serious public health threat.)

People looking to get rid of their aquarium fishes, says U.S.G.S. biologist Pam Fuller, should consider returning them to the local pet shop, giving them to another hobbyist or donating them to a public aquarium, school or hospital.