Strips head off fish (4)
I believe the answer is:
eels
'fish' is the definition.
(I've seen this before)
'strips head off' is the wordplay.
'strips' becomes 'peels' (peeling is a kind of stripping).
'head off' means to remove the first letter.
'peels' with its initial letter taken off is 'EELS'.
(Other definitions for eels that I've seen before include "Elongated fish" , "Long fishes" , "Slender fishes" , "Food for Cockney" , "Slippery customers" .)