Find fault with fish (4)
I believe the answer is:
carp
I believe this is a double definition.
'find fault' is the first definition.
(I've seen this before)
'fish' is the second definition.
(carp is a kind of fish)
'with' acts as a link.
(Other definitions for carp that I've seen before include "ish" , "Fish; find fault continually" , "Pond fish" , "Raise trivial objections" , "Keep complaining" .)