Bone goes with third of fillets, fishy Italian dish (9)
I believe the answer is:
bolognese
'italian dish' is the definition.
(spaghetti Bolognese)
'bone goes with third of fillets fishy' is the wordplay.
'with' is a charade indicator (letters next to each other).
'third of fillets' becomes 'l' (3rd letter of 'fillets').
'fishy' is an anagram indicator.
'bone'+'goes'+'l'='bonegoesl'
'bonegoesl' anagrammed gives 'BOLOGNESE'.
(Other definitions for bolognese that I've seen before include "See 22" , "Spaghetti dish" , "Pasta dish (from an Italian city)" , "Meat and tomato sauce" , "Spaghetti sauce" .)