The Dolphins of Pern by Anne McCaffrey

In this latest addition to McCaffrey's popular Pern series (Chronicles of Pern: First Fall, etc.), the humans of Pern are reunited, after eons of noncontact, with the intelligent dolphins who had originally settled the planet with them. When a boy, Readis, is rescued by "shipfish" and realizes that they can talk, he develops a lifelong obsession with the fascinating creatures. But, though his interest is shared by the young dragonrider T'Lion and his dragon, Gadareth, it is forbidden by his mother...