The Legend of Zelda Phantom Hourglass Walkthrough part 13

The fishing side-quest. If you want all heart containers, you're gonna have to do this side-quest.

To get the Big Catch Lure, you need to catch at least one Skippyjack, one Toona and one Loovar. When you catch one of these fish for the first time, make sure you show it to the Old Wayfarer to get a random treasure.