Fishing is tied to the mouse invert option that controls looking, however fishing is opposite.
As it is now::
If you have default setting:
Look- Up is Up & Down is Down
Fishing - Up is down & Down is up.
If you invert it:
Look - Up is down & Down is up.
Fishing - Up is Up & Down is Down
This is counter intuitive.
When I found out how to invert it, I could actually catch fish. The downside is I have to access the options menu every time I switch from fishing to another task.