You need to fish 2 fish near the cat's peir. The fishing itself is what's giving a lot of peeps problems.
Just jiggle (or shake as the manual says, but it doesn't feeling like shaking up and down( the bloat so it's shaking halfway out of the surface of the water. Your goal is to get the float bouncing up and down on the surface of the water while it is half submerged. When it sinks snap the wiimote up and hope you catch a fish. Hold the wiimote up (not too high, seems too far offscreen doesn't work) to pull it out.
Yeah, it's pissed off a lot of people. Just keep at it, its gets easier once you can use bait after this and even easier when lure fishing.