How to cook
Be sure to pick out fresh Mediterranean horse mackerels, clean them thoroughly of their heads and insides. Rinse them well with cold water, put them in a suitable container and pour on the brine, made by dissolving the salt in 4 1/5 cups (1 L) cold water.
Leave the fish for 24 hours in the fridge, then drain out the brine and pour on apple cider vinegar so that it covers the mackerels evenly.
Pour a little oil that you've heated and then cooled into the jars, to prevent any air from reaching the fish.
Store in a dark and ventilated area.
Consume in pleasant company.
I haven't listed exact quantities of marinade and servings because they depend on how many fresh mackerels you'll be marinating.
Source: Stoyan Stoyanov from Culinary Network.