Pickling fish is a common Scandinavian technique. Originally conceived to preserve the fish, it is now used to add flavour and sharpness. Oily fish are particularly well-suited to pickling, which is why pickled mackerel is one of the most common pickled fish you'll find.
While you can buy pickled mackerel in the shops, it's incredibly easy to make at home and means it will be free from unnatural preservatives and you have total control over the flavours in the pickling liquor. Always use the freshest fillets you can find. The pickled mackerel recipe below is a great starting point, but do get inventive with herbs, spices and aromatics in the pickling liquor to add even more flavour – simply add them to the pan along with the water, vinegar, sugar and salt.