Marine Hunter

Marine Hunter (マリンハンター, Marin Hantā) is a Japanese manga series written and illustrated by OOTSUKA Shirou.

Plot
At the end of the 21st century, the earth is covered with Human/fish hybrids. Water almost completely surrounds earth and so these hybrids known as "Fish-halfs" roam the waters. A girl named Guppy is rescued by a hybrid named Shark, who wants nothing more than killing off the navy (who try to control him).