Guy picked up fish drink (7)
I believe the answer is:
cordial
'drink' is the definition.
(cordial is a kind of drink)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for cordial that I've seen before include "7 [HEARTY]" , "Agreeable - drink" , "Affable type of sweet drink?" , "stimulating drink" , "drink with a fruity flavour" .)