Season the herring with salt and rub with olive oil. Place in a hot non stick frying pan and cook for 2 minutes on each side.
Meanwhile, slice the fennel very thinly either with a knife or on a mandolin, keeping the root intact then put into a bowl.
Remove the skin from the grapefruit and remove the segments then add to the fennel in the bowl. Then add a squeeze of lemon juice, maldon salt, capers, parsley and mix together with a drizzle of olive oil.
To serve, place the fennel and grapefruit salad on the plate, top with this fish then season with a squeeze of lemon juice and sprinkle with caper berries.