Fowl, fish and insect (9)
I believe the answer is:
cockroach
'insect' is the definition.
(cockroach is a kind of insect)
'fowl fish' is the wordplay.
'fowl' becomes 'cock' (cock is a kind of fowl).
'fish' becomes 'roach' (roach is a kind of fish).
'cock'+'roach'='COCKROACH'
'and' acts as a link.
(Other definitions for cockroach that I've seen before include "Beetle-like insect" , "Rock coach turns out to be an insect" , "Household insect pest" , "See pest" , "So-called black beetle" .)