Aquatic subtype would need to have amphibious, not water breathing. I prefer water subtype and water breathing. (A little odd, though, since their "cousin" the copper dragon is earth subtype.)
Definitely cleric and domain spells. Since they favor "conjuration/summoning and alteration" (transmutation, I guess) spells and are CN and water-related, maybe Chaos, Water, and Creation domains? Not a lot of transmutations in there, but lots of conjuration and some "alteration-like" abjurations.
Definitely Swim. Maybe Spellcraft since they like to use spells more than melee. And Appraise for valuing the gifts they receive. I wouldn't mind a small racial penalty to Sense Motive.