Haircut — fish (6)
I believe the answer is:
mullet
I believe this clue is a double definition.
'haircut' is the first definition.
(hair style)
'fish' is the second definition.
(I know that mullet is a type of fish)
(Other definitions for mullet that I've seen before include "swimmer" , "Fish (red or grey)" , "Fish, male hairstyle" , "Barnet?" , "Fish's name for a hairstyle" .)