 | Rex Reason als Dr. Thomas Morgan |
 | Jeff Morrow als Dr. William Barton |
 | Leigh Snowden als Marcia Barton |
 | Gregg Palmer als Jed Grant |
 | Maurice Manson als Dr. Borg |
 | James Rawley als Dr. Johnson |
 | David McMahon als Capt. Stanley |
 | Paul Fierro als Morteno |
 | Lillian Molieri als Mrs. Morteno |
 | Frank Chase als Steward |
 | Larry Hudson als State Trooper |
| Ricou Browning als The Gill Man (in water)(uncredited) |
 | Don Megowan als The Gill Man (on land)(uncredited) |
 | George Sowards als Ranch Hand (uncredited) |
| John Sherwood | Director |
| William Alland | Producer |
| Arthur A. Ross | Screenplay |
| Arthur A. Ross | Story |
| Irving Gertz | Original Music Composer |
| Henry Mancini | Original Music Composer |
| Heinz Roemheld | Original Music Composer |
| Maury Gertsman | Director of Photography |
| Edward Curtiss | Editor |
| Alexander Golitzen | Art Direction |
| Robert Emmet Smith | Art Direction |
| John P. Austin | Set Decoration |
| Russell A. Gausman | Set Decoration |
| Joan St. Oegger | Hairstylist |
| Vincent Romaine | Makeup Artist |
| Eddie Pyle | Camera Operator |
| Lew Schwartz | Assistant Camera |
| Max Nippell | Gaffer |
| Julius Rosenkrantz | Props |
| Leslie I. Carey | Sound |
| Robert Pritchard | Sound |
| Peter Berkos | Sound Editor |
| Robert L. Bratton | Sound Editor |
| George Hoagland | Sound Editor |
| Clifford Stine | Visual Effects Camera |
| Jay A. Morley Jr. | Costume Design |
| Roger J. Weinberg | Costume Design |
| Jack Kevan | Makeup Effects Designer |
| Clifford Stine | Visual Effects |
| Bud Westmore | Makeup Supervisor |
