Fish in Polperro, a chub? (5)
I believe the answer is:
roach
'fish' is the definition.
(roach is a type of fish)
'in polperro a chub?' is the wordplay.
'in' indicates a hidden word.
'ROACH' is hidden in the letters of 'polperro a chub'.
(Other definitions for roach that I've seen before include "Fish - part of a cannabis cigarette" , "joint near the end" , "Fresh-water food fish" , "Animal found in the water" , "Historic SE county" .)