Prosecuted about fish that's sickly (7)
I believe the answer is:
sugared
'sickly' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'prosecuted about fish' is the wordplay.
'prosecuted' becomes 'sued' (I've seen this before).
'about' is an insertion indicator.
'fish' becomes 'gar' (I've seen this before).
'sued' going around 'gar' is 'SUGARED'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for sugared that I've seen before include "Sweetly coated (almond)" , "Sweetened" .)