Commonly found in the aquarium trade, oscars (Astronotus ocellatus) are often a colorful household pet. They tend to overstay their welcomes quickly, however, growing too large and feeding on other fish. When aquarium owners finally give up, as so many have since at least the late 1950s, oscars are returned to the wild. In fact, oscars are so popular, they have been found throughout the United States, even as far as Hawaii. The fish in this photo was found in Nebraska, for example.
A wild habitat isn't the same a native one, however. The oscar instead originate from South America, found around the Orinoco and Amazon basins, French Guyana and northern Paraguay, according to USGS. But the fish don't mind the surroundings, feeding on small fish, insects and crustaceans of the Everglades or other large freshwater areas.
Anglers don't mind the oscars either. The hard-fighting fish ranks second in popularity only to large-mouth bass, notes the Florida Fish and Wildlife Commission. The oscar's meat is white and flaky, but eating too much isn't recommended because of mercury contamination.
Native fish do likely take exception to the oscars' presence, however. The oscars prey on some species, and compete for food and spawning areas with others.
Oscars aren't the only non-native species that made their way from aquaria to the wild. Other examples include lionfish, the Mayan cichlid and the walking catfish, all of which are a serious detriment local plant and animal species.
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Photo credit: Nebraska.gov