The Beach Girls and the Monster (1965)

Go! Go! Go! The Coolest Monster Shindig of Chicks and Chills!

A young girl is killed at the beach in Malibu. Professor Otto Lindsay suspects that it is some form of mutated fish. However, his son Richard, who was a good friend of the girl, thinks that it is a madman who has a grudge against Richard and his friends. Soon the list of victims grows.