The accident occurred Tuesday in Maine, near O'Hare International Airport, the Chicago Tribune reported.
Frank Bilecki, a spokesman for the Cook County Sheriff's Department, said when the parents heard their 18-month-old daughter crying and found her missing a fingertip they first blamed their pit bull. But a doctor at Advocate Lutheran General Hospital in Park Ridge told him the bite had not been inflicted by a dog.
The father rushed home, grabbed a piranha from the tank and cut it open, finding his daughter's fingertip, Bilecki said. The family had two of the fish, sharp-toothed carnivores from South America.
Bilecki said child welfare workers investigated the family and decided the parents and their daughter were victims of an accident.
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