Ninety degrees, say, needed for fish (5)
I believe the answer is:
angle
This clue is a double definition.
'ninety degrees say' is the first definition.
(ninety degree angle)
'fish' is the second definition.
(angle can mean to fish)
'needed for' acts as a link.
(Other definitions for angle that I've seen before include "Early settler" , "crook" , "Fish with hook and line" , "Heat (metal) and allow to cool to remove stresses" , "Right, acute or obtuse" .)