sea ponys for every one and yea we would be breathing fish pee and poop whith are own blek .sea ponys and some of you arent very good at making up stuff isnt this a fun thing
ok, I'm thinking you guys would like to read the book, "The Abyss", by Orson Scott Card. It's definately no literary giant but, as for adapting to breathing underwater and some of your hypotheticals, there are some creative answers right there. Go get it...