Fish that’s rotten brought up (3)
I believe the answer is:
dab
'fish' is the definition.
(dab is a type of fish)
'rotten brought up' is the wordplay.
'rotten' becomes 'bad' (similar in meaning).
'brought up' is a reversal indicator (in a down clue, letters go up).
'bad' written backwards gives 'DAB'.
'that's' acts as a link.
(Other definitions for dab that I've seen before include "Gently wipe" , "Bad kind of fish" , "Flounder" , "Flatfish; fingerprint" , "Fingerprint - fish" .)