Fibre fine served with Scandinavian fish (4)
I believe the answer is:
flax
'fibre' is the definition.
(flax is a kind of fibre)
'fine served with scandinavian fish' is the wordplay.
'fine' becomes 'f' (abbreviation).
'served with' is a charade indicator (letters next to each other).
'scandinavian fish' becomes 'lax' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'f'+'lax'='FLAX'
Can you help me to learn more?
(Other definitions for flax that I've seen before include "leaves from it make cloth" , "Fibre woven to make linen" , "Source of linen" , "Linen fibres" , "Blue flowering plant cultivated for its seeds and fibre" .)