Extract metal from fish (5)
I believe the answer is:
smelt
This clue is a double definition.
'extract metal from' is the first definition.
(I've seen this in another clue)
'fish' is the second definition.
(I know that smelt is a type of fish)
(Other definitions for smelt that I've seen before include "Inhaled odour" , "Extract metal from ore, fish" , "Produce metal by heat" , "Extract (metal) from ore by heat" , "Small silvery fish" .)