Caught a whiff of fish (5)
I believe the answer is:
smelt
I believe this is a double definition.
'caught a whiff' is the first definition.
'fish' is the second definition.
(smelt is a kind of fish)
'of' is the link.
(Other definitions for smelt that I've seen before include "Food fish often fried" , "Sniffed - fish" , "Small fish of salmon species" , "Extract (metal) from ore by heat" , "Fish related to the salmon (which ponged?)" .)