- Marine Boy's mermaid girlfriend, Neptima, was topless (although her hair always covered her breasts). No other children's animated show has ever dared to do this.
- Marine Boy's dolphin was actually named Whitey in the Japanese version. It was changed to Splasher for the American market to avoid accusations of racism.
- Although Marine Boy's "oxygum" supplied his air, the effects of pressure and depressurization were conveniently ignored.
- Neptima's pearl, besides being a defensive weapon, also showed glimpses of future events.
- Neptina's origin was never explored, nor how she and Marine Boy became friends.
- Marine Boy's mother was never shown.
