Catfish husband to reveal cheat (5)
I believe the answer is:
welsh
'cheat' is the definition.
(I know that welsh is a more specific form of the action cheat)
'catfish husband' is the wordplay.
'catfish' becomes 'wels' (I've seen this before).
'husband' becomes 'h' (abbreviation).
'wels'+'h'='WELSH'
'to reveal' acts as a link.
(Other definitions for welsh that I've seen before include "Cymric" , "Default on bet in Wales?" , "Nationality of Dai or Ivor" , "From a principality" , "Owain Glyndwr?" .)