Sri-La Village is also home to another new fishing addition: the Engorged Sea Monster. By fishing in a Large Swarm of Migrated Reef Octopus (what triggers the spawn of this pool, we don't yet know), you might fish up the sea monster and its 39 million health. While currently bugged to do no damage on the PTR, it's unlikely to go live that way, so you probably won't want to try soloing this fellow. The sea monster's loot is not yet implemented.
Fishing has also been given four brand new battle pets: Tiny Blue Carp, Tiny Green Carp, Tiny Red Carp, and Tiny White Carp. Lead Content Design Cory Stockton (also known as Mumper) described where to acquire these fishies on Twitter: