Abu Ibrahim thought he had a maneater on his hands when he reeled the "piranha" onshore at Castaic Lake Monday. Turns out the fish is actually a mild-mannered cousin called a "pacu", with a far less fearful demeanor. The pacu is primarily a plant eater, unlike the notorious piranha that feeds on flesh. State fish & game officials say it's not the first time a species like this has been pulled from Castaic Lake. Apparently, people tend to throw them into lakes & streams when the creature becomes too big for their aquariums.