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NORTHPERRY, Ohio-- The mystery surrounding two goldfish discovered inside the Perry Nuclear power plant has been solved.

Officials with FirstEnergy say two contract workers admitted to placing the fish in an underground steam tunnel.

They said it was a practical joke, but we have learned that "joke" could ban them from working in another U.S. nuclear plant for good.

Four other workers admitted to investigators that they knew about the prank, but didn't tell anyone.