Large skin blemish shows up in thorough search (5)
I believe the answer is:
trawl
'thorough search' is the definition.
'large skin blemish shows up' is the wordplay.
'large' becomes 'l'.
'skin blemish' becomes 'wart' (I've seen this before).
'shows up' shows that the letters should be reversed in order.
'l'+'wart'='lwart'
'lwart' reversed gives 'TRAWL'.
'in' is the link.
(Other definitions for trawl that I've seen before include "Fishermen may use it" , "seek suitable candidates" , "Fishing dragnet" , "Fish commercially with nets" , "Drag a large net" .)