If you're looking for manga similar to Triton of the Sea, you might like these titles.
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).
Shachi, a young fisherman who lives in an peaceful island, is involved in a tragic event that reminds him the death of his father, which happened years ago.The boy then decides to start a journey in the mysterious ocean.
In a post-apocalyptic world covered with water, Wadatsumi, a person who lives in what appears to be the last piece of land, finds a mysterious girl dragged by the waves of the sea. Where does she come from? Are there other lands in this world?
Sixteen years after the great hydroseism, nearly the entire world has sunken beneath the seas... but that won't stop Tatsumiya Minato from following her dream of becoming a high school student at the Enoshima Women's Ocean Academy!
When his ship is attacked by pirates, Archer is left floating adrift in a violent sea. But the young urchin is nothing if not resilient. He soon finds himself sailing with the infamous Cannonball Joe aboard "La Revancha," the fastest ship on the East Coast, in search of a legendary cache of hidden treasures. Their dangerous quest will lead directly to a showdown with the "Hoboken," one of the most feared pirate vessels ever to sail the Jersey shores, and its reckless captain, Lee. But there are far worse things than pirates that call these waters home...
In the future the world is taken over by the Ocean Empire. The Earth's only hope lies with the Super 99, a submarine designed by Dr. Juzou Oki.The story follows Susumu Oki, the chief mechanic of the SS-99 and the adventures he and the other crew members take on the SS-99 to save Earth.
It's about the coastal lifeguard, as Hyogo Kanbayashi tried to make his way through to enter Tokkyuu, the elite lifeguard team.
Nagisa has just recently transformed from being a human to a mermaid and is easing into the transition of living in the ocean. But when she crashes into a research submarine, she loses her memory and is brought on board the Sogei. It turns out that her love interest from when she was still human, Osanai, is on board and he tries to keep his past with Nagisa a secret from everyone else. Her mermaid friend, Tsunami, goes on a rescue mission to find Nagisa and warn her that since she just transformed into a mermaid, if she doesn’t speak for an hour, she turns back into a human and her life expectancy will dramatically drop!
Retired deep-sea diver Albert goes on one final job to recover a unique, once in a lifetime treasure, which is said to be inside the safe of a U-Boat, 620 meters under sea. Together with his old team, the treasure hunters known as DEEP, the mission to recover the safe begins...?