Doctor is enthralled by fish in Arctic feature (6)
I believe the answer is:
tundra
'arctic feature' is the definition.
(arctic region)
'doctor is enthralled by fish' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'is enthralled by' indicates putting letters inside ('enthral' can mean 'capture').
'fish' becomes 'tuna' (tuna is a type of fish).
'dr' put into 'tuna' is 'TUNDRA'.
'in' acts as a link.
(Other definitions for tundra that I've seen before include "Vast flat treeless zone" , "Northern permafrost region" , "Area of permafrost" , "Russian countryside?" , "Area of permanently frozen subsoil" .)