Blame salesperson over fish (8)
I believe the answer is:
reproach
'blame' is the definition.
(I've seen this before)
'salesperson over fish' is the wordplay.
'salesperson' becomes 'rep' (I've seen this before).
'over' means one lot of letters go next to another.
'fish' becomes 'roach' (roach is a kind of fish**).
'rep'+'roach'='REPROACH'
(Other definitions for reproach that I've seen before include "Censure - or preach (anag)" , "Take to task" , "Express disapproval, admonish" , "Blame, scold" , "Berate" .)