The fish, the only one of its kind found, survived for a few days but eventually died. Officials say it's unlikely it reproduced in Caribou, which is adjacent to Pike Lake.

Doug Jensen, Minnesota Sea Grant invasive species expert, said the fish probably was released out of a local resident's aquarium, an increasingly common problem.

While seemingly a harmless prank or thoughtless disposal, the influx of foreign fish into local waters can be serious. Although many exotic fish can't survive here, others can, and they could threaten local fish populations. Non-native animals and plants can impair water quality, compete with native species and carry diseases that may be transmitted to native fish, Jensen said.

Last year, crews drained Rock Pond at the University of Minnesota Duluth to get rid of goldfish and other exotic species that were reproducing, surviving through Duluth winters and that could have moved into a connected trout stream and Lake Superior.

Instead of dumping fish in local waters, people are asked to return them to the pet or aquarium store where they were purchased, give them to another aquarium owner or donate them to a school or business that has an aquarium.

Brian Mattson, owner of Superior Aquarium in Superior, is part of a national effort by the aquarium industry to offer proper disposal or trading of unwanted fish. Mattson said people are welcome to call him for tips on turning back fish.