Turn over to clean small herring fillets (8)
I believe the answer is:
rollmops
'herring fillets' is the definition.
(I've seen this before)
'turn over to clean small' is the wordplay.
'turn over' becomes 'roll' ('roll' can be a synonym of 'turn over'**).
'to clean' becomes 'mop' (mopping is a kind of cleaning).
'small' becomes 's' (abbreviation - e.g. clothes size).
'roll'+'mop'+'s'='ROLLMOPS'
(Other definitions for rollmops that I've seen before include "fish food" , "Raw herring fillets" , "Pickled herrings" , "Rolled and pickled herring fillets" , "Herrings wrapped around pickles" .)