I asked Lenn (because I know someone will): "Have you ever tried out gillyweed?"
"I kept hearing about it for the longest time, but I've never been anywhere near where it grows, so I only got to try it after getting my anthro form. It's really cool, and affects my two forms differently! No matter what, it gives me gills and makes my flukes vertical, but in my anthro form it also makes a fin along my tail and makes my dorsal fin bigger. In my feral form, it actually turns my flippers into long fins! Haven't figured out much use for them like that, but still, it's cool. And, you know... Breathing underwater is pretty sweet! Wish I could still breathe air while the effect is going, but it's still a lot of fun."