Rex Reason
Dr. Thomas Morgan
Acting
Jeff Morrow
Dr. William Barton
Acting
Leigh Snowden
Marcia Barton
Acting
Gregg Palmer
Jed Grant
Acting
Maurice Manson
Dr. Borg
Acting
James Rawley
Dr. Johnson
Acting
David McMahon
Capt. Stanley
Acting
Paul Fierro
Morteno
Acting
Lillian Molieri
Mrs. Morteno
Acting
Frank Chase
Steward
Acting
Larry Hudson
State Trooper
Acting
Ricou Browning
The Gill Man (in water)(uncredited)
Acting
Don Megowan
The Gill Man (on land)(uncredited)
Acting
George Sowards
Ranch Hand (uncredited)
Acting