Find fault with the fish (4)
I believe the answer is:
carp
This clue is a double definition.
'find fault' is the first definition.
(I've seen this in other clues)
'fish' is the second definition.
(carp is a kind of fish)
'with the' is the link.
(Other definitions for carp that I've seen before include "Continually nag; fish" , "Fish; nag pettily" , "Cavil - fish" , "Raise petty objections about goldfish" , "Fish; find fault continually" .)