Patch 7.1 adds a new aquatic mount called the Darkwater Skate. It can be purchased from the Fishing Vendor Galissa Sundew on the Darkmoon Isle for 500x Darkmoon Daggermaws. Many players will want to get this new aquatic mount as there's no flying in Legion and not only that, it looks really cool.
Start hoarding Darkmoon Daggermaw! If you're the Fishing type of a player, head over to the Darkmoon Isle and fish out daggermaws. If you're not much into Fishing and consider farming a waste of time, check out your Auction House for the fish and make sure to buy cheap and resell at higher prices. Just be patient. If your stacks don't sell overnight, don't worry. Try to undercut your auctions frequently, at least 3 times a day or more (on very populated realms) as there's a lot of competition. To check out daggermaw prices for your realm, visit the Undermine Journal.