Method of payment for fish (3)
I believe the answer is:
cod
This clue is a double definition.
'method of payment' is the first definition.
(I've seen this before)
'fish' is the second definition.
(type of fish)
'for' acts as a link.
(Other definitions for cod that I've seen before include "method of payment" , "catch!" , "Common food fish" , "Edible fish" , "Pay when you get the goods - sounds fishy" .)