If you're looking for anime similar to Triton of the Sea (1979), you might like these titles.
Ganbare, a black fish born into a shoal of red fish, tries to fit in amid adventures as he is chased by tuna and must evade the Great Octopus.
The ruler of the underground world, is planning to conquer the whole world. Riding the fire dragon Isamu and Angel, the princess of the undersea kingdom, try to stop him from destorying their world.
Yamato and Momonosuke look back on Oden's adventures and heroic actions throughout the world and in the Land of Wano. Yamato describes for Momonosuke all the joy and pain that his father went through during his days.
An old fisherman goes out on his fishing trip and makes a huge catch, the biggest of his life.
Teenage Marine Boy battles evil on and under the seas on behalf of the Ocean Patrol - aided by the amazing inventions of his father, Dr. Mariner and the brilliant Professor Fumble. Joining Marine Boy in his mission are his white dolphin, Splasher, young mermaid Neptina, and fellow Ocean Patrol agents Bullton and Piper. Get ready to dive into the amazing aquatic animated adventures of Marine Boy!