Malodorous fish is irritating (8)
I believe the answer is:
rankling
'irritating' is the definition.
(rankling is a kind of irritating)
'malodorous fish' is the wordplay.
'malodorous' becomes 'rank' ('rank' can be similar in meaning to 'malodorous').
'fish' becomes 'ling' (ling is a kind of fish).
'rank'+'ling'='RANKLING'
'is' is the link.
(Other definitions for rankling that I've seen before include "causing some bitterness" , "annoying" , "vexing" , "Causing endless annoyance" , "leaving a nasty taste in one's mouth" .)