Fish on left for show (7)
I believe the answer is:
portray
'show' is the definition.
(I've seen this before)
'fish on left' is the wordplay.
'fish' becomes 'ray' (ray is a kind of fish).
'on' says to put letters next to each other.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'ray' put after 'port' is 'PORTRAY'.
'for' is the link.
(Other definitions for portray that I've seen before include "Depict, present" , "Delineate" , "Play" , "Show" , "Use words to describe" .)