User blog comment:12th Supernova/Chapter 824: You're playing with the big boys now/@comment-12333373-20160421125717/@comment-5774380-20160421175804

Second that. The "holding his breath" theory doesn't make much sense, he's been underwater for several hours and to hold his breath for so long while being weakened by the sea would be beyond badassery (and also a very shitty deus ex machina). And the fact that his sharp teeth had remained hidden and are coincidentally revealed at the same time that we learn of his ability to survive underwater is an evident hint of his fishman blood.