Bar code's heading scanned backwards to find fiddler? (4)
I believe the answer is:
crab
'fiddler?' is the definition.
(fiddler crab is a type of crab)
'bar code's heading scanned backwards' is the wordplay.
'heading' suggests taking the first letters (head could mean the top letter).
'scanned backwards' shows that the letters should be reversed in order.
The initial letter of 'codes' is 'c'.
'bar'+'c'='barc'
'barc' in reverse letter order is 'CRAB'.
'to find' acts as a link.
(Other definitions for crab that I've seen before include "Ten-legged shellfish" , "Pincered crustacean" , "terrible row" , "Seafood (that can be caught by a rower?)" , "Scuttling crustacean" .)