A way to spoil fish (8)
I believe the answer is:
turnpike
'a way' is the definition.
(turnpike is a kind of way)
'spoil fish' is the wordplay.
'spoil' becomes 'turn' (I've seen this in another clue).
'fish' becomes 'pike' (pike is a kind of fish).
'turn'+'pike'='TURNPIKE'
'to' is the link.
(Other definitions for turnpike that I've seen before include "Old gates across a road to prevent passage until a toll was paid" , "A paying way" , "Old barrier" , "way in the US" , "American highway" .)