Got this off wikipedia -
In a second season episode of Homicide: Life on the Street, a Jack Dempsey is recovered at the scene of a murder, and is taken home by an unsuspecting Detective John Munch, who intends to give it to his tropical fish-collecting girlfriend as a present. As a surprise, he places the fish in her aquarium, where it proceeds to devour $4,000 worth of her fish before being removed. Munch later refers to the fish as an "assassin" who "uses piranhas as toothpicks."
In a second season episode of Homicide: Life on the Street, a Jack Dempsey is recovered at the scene of a murder, and is taken home by an unsuspecting Detective John Munch, who intends to give it to his tropical fish-collecting girlfriend as a present. As a surprise, he places the fish in her aquarium, where it proceeds to devour $4,000 worth of her fish before being removed. Munch later refers to the fish as an "assassin" who "uses piranhas as toothpicks."