Mermaid Man & Barnacle Boy

Mermaid Man and Barnacle Boy are a semi-retired superhero duo from SpongeBob SquarePants. They are either humans who's powers allow them to breath underwater or they're Apparently Human Merfolk, with their own grab-bag of swimming-based super-moves, the ability to summon sea-life to help them and a variety of gadgets and gizmos to help fight evil. In "Mermaid Man and Barnacle Boy V", it's revealed that they were once a part of a Super Team that protected the seas named the The International Justice League of Super Acquaintances, and even then Mermaid Man and Barnacle Boy were the only ones with a clear aquatic theme to them.

Example of:
Captain Fishman