How about a pacu or piranha-caju? I think they're the same.
From two sources:
Found in New Hampshire pond; "The fish was taken to the Fish and Game Department, where expert Steve Perry identified it as a fruit-eating piranha, or Pacu, from South America."
On the p-c; "Some, like the piranha-caju, even have large molars and strong jaw muscles to crack nuts."
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