Vermin repulsed fish and bird (8)
I believe the answer is:
starling
'bird' is the definition.
(starling is a kind of bird)
'vermin repulsed fish' is the wordplay.
'vermin' becomes 'rats' (I've seen this before).
'repulsed' shows that the letters should be reversed in order.
'fish' becomes 'ling' (ling is a kind of fish).
'rats' backwards is 'star'.
'star'+'ling'='STARLING'
'and' acts as a link.
(Other definitions for starling that I've seen before include "Gregarious bird" , "Common songbird" , "flier" , "Bird from heavenly body and fish" , "Dark, glossy bird" .)