Despite him breathing the air normally, the little flaps of skin fluttered softly with every breath.
"Of course, they're much better noted underwater," he said, slipping back down under the surface.

There the gills went to work, moving gracefully as he breathed the water. Triton gave her a couple minutes to admire them, but then moved to kiss her. At least, in part. He soon began to breathe for the both of them.