Catching fishes in MHW is a little buggy specially with W button not working for PC users but with a little patient you can complete Kanya's quest.

Lure the Fish

1. Find a fish in the water around Kanya.

2. Aim for as close as possible to fish's mouth.

3. Movie left and right (or up and down) until the fish gets interested in biting your lure.

4. Now wait for fish's bite.