Find fish around river with it (6)
I believe the answer is:
rarity
'find' is the definition.
(I've seen this before)
'fish around river with it' is the wordplay.
'fish' becomes 'ray' (ray is a kind of fish).
'around' indicates putting letters inside.
'river' becomes 'r' (abbreviation for river).
'with' means one lot of letters go next to another.
'r'+'it'='rit'
'ray' placed around 'rit' is 'RARITY'.
(Other definitions for rarity that I've seen before include "Uncommon item or event" , "Uncommon thing" , "something out of the ordinary" , "Something very scarce, probably valuable" , "Collector's item" .)