Dangerous Passage

Dangerous Passage is a 1944 American film directed by William Berke, starring Robert Lowery and Phyllis Brooks.

On the ship, the Merman, is Dawson Alec Craig, a steward who helped Joe against his unknown assailant. Also on the ship are Captain Saul William Edmunds and his mate, Buck Harris Victor Kilian. Among the few passengers is the alluring Nita Paxton Phyllis Brooks, who a cabaret artist whom Joe takes a liking to the minute he boards the ship.Before the ship lands in its first port on the cruise, Dawson is murdered, and Joe gets rid of the body by feeding it to the fish, to avoid being blamed for his death. On shore in Los Altos, Joe and Nita go off romancing together. Upon their return to the ship, Joe discovers that Bergstrom has come aboard and brought a man calling himself Joe Beck Jack La Rue. Joe instantly suspects Nita of being in cahoots with Bergstrom, trying to trick him out of his inheritance. She then confides in him, that Dawson was an undercover agent for an insurance company, suspecting the captain and his crew of insurance fraud. She is trying to finish his work after he disappeared. ........

Source: Wikipedia