Rick Riordan said this quote
“ Frank couldn't breathe underwater.But where was he?Percy turned in a full circle. Nothing. Then he glanced up. Hovering above him was a giant goldfish. Frank had turned -clothes, backpack, and all- into a koi the size of a teen-aged boy.dude. Percy sent his thoughts through the water, the way he spoke to other sea creatures. A goldfish?Frank's voice came back to him: I freaked. We were talking about goldfish, so it was on my mind. Sue me. ”