Venue for fish, say (5)
I believe the answer is:
place
'venue' is the definition.
(I know that venue can be written as place)
'fish say' is the wordplay.
'fish' becomes 'plaice' (plaice is a kind of fish).
'say' indicates a 'sounds like' (homophone) clue.
'plaice' is a homophone of 'PLACE'.
'for' is the link.
(Other definitions for place that I've seen before include "Locus" , "Put in - winning position" , "Situation" , "Locate" , "Identify -- station" .)