Like Arctic fish that wriggles in lock (8)
I believe the answer is:
treeless
'like arctic' is the definition.
(the Arctic is generally treeless)
'fish that wriggles in lock' is the wordplay.
'fish that wriggles' becomes 'eel'.
'in' indicates putting letters inside.
'lock' becomes 'tress' (both can mean a piece of hair).
'eel' placed within 'tress' is 'TREELESS'.
(Other definitions for treeless that I've seen before include "With no very large plants" , "Like a plain" , "Like the Arctic" , "like down, say" , "As the Nullarbor Plain (if its name is to be believed)" .)