I finally managed to buy some fresh sardine fillets today. George's Seafood at West End have them in stock along with heaps of other Australian fish. If they don't have the fillets already prepared, they'll fillet while you wait.
I'm making pickled fish by lying the fillets in a dish and covering with lime juice, salted capers and fresh dill. I'll leave on the bench for one day and they'll be ready for eating. No enzymes damaged by heating. Just before I plate them, I'll add some cultured cream to finish off.
How to culture fresh cream? Just buy, hopefully, unpasteurised organic cream and add a capsule of probiotic, stir through and leave on bench for one day. If you have kefir milk in the fridge, you can add a small amount to the cream and that will innoculate the cream. Healthy bacteria for the gut and easily digestible.