Based on the first book in a trilogy by Danish novelist Bjarne Reuter, Zappa proved an early international breakthrough for its director, Bille August. The story of three teenagers in 1960s Copenhagen is really no big literary accomplishment -- the boys become delinquents because of their parents' inattentiveness in particular and a decadent society in general -- but August elicited wonderful performances from his young, inexperienced cast, especially Adam Tønsberg, as the lower-middle-class boy with upward mobile pretensions, and Peter Reichhardt as the thoroughly vicious Steen, whose carnivorous pet fish gives the film its name. The son of Danish matinee-idol Poul Reichhardt, Peter Reichhardt offered a truly frightening portrayal of contained malice. Director August filmed the second novel in Reuter's youth trilogy, Tro, Håb og Kærlighed, the following year.
~ Hans J. Wollstein, All Movie Guide