Fish in the corner (5)
I believe the answer is:
angle
This clue is a double definition.
'fish' is the first definition.
(angle can mean to fish)
'the corner' is the second definition.
(eg a corner of a shape)
'in' is the link.
(Other definitions for angle that I've seen before include "Ancient German, fish" , "Perspective" , "Gradient" , "Approach to problem" , "Point of view; old tribesman" .)