Bird, fish, or insect (9)
I believe the answer is:
'insect' is the definition.
(I've seen this before)
'bird fish' is the wordplay.
'bird' becomes 'cock' (cock is a kind of bird).
'fish' becomes 'roach' (roach is a kind of fish**).
'or' acts as a link.
(Other definitions for cockroach that I've seen before include "Rock coach turns out to be an insect" , "Beetle-like insect" , "Household insect pest" , "See pest" , "Cork coach can be a pest" .)