A pacu is a breed that's related to the piranha.
Steve Gruebel owns Cameo Pet Shop in Queens. He got Buttkiss in 1967 when he was just a wee thing. He sold him a year later when Buttkiss was two inches long. But in 1970, Buttkiss was returned when he outgrew the buyer's tank.
Buttkiss lives in only a four-foot-long, 75-gallon tank. Gruebel says he's afraid to move him because he may not survive the changing environment.
Buttkiss is beginning to show his age. He has arthritic gills and glaucoma in his right eye.