Fish in river caught by one hoping to make profit? (5)
I believe the answer is:
trout
'fish' is the definition.
(I know that trout is a type of fish)
'river caught by one hoping to make profit?' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'caught by' means one lot of letters goes inside another.
'one hoping to make profit?' becomes 'tout' (eg a ticket tout).
'r' going inside 'tout' is 'TROUT'.
'in' is the link.
(Other definitions for trout that I've seen before include "Game fish related to salmon" , "Rainbow, for example" , "Rainbow, say" , "Mistiness" , "grumpy old woman" .)