To make the seasoning, place the vinegar, sugar and salt in a saucepan, bring to a boil, reduce to a simmer and stir until the ingredients are dissolved.
Place the rice in a colander and wash thoroughly under cold running water. Leave the rice to soak in a saucepan with the 550ml of water for 30 minutes.
Bring the rice to the boil and then reduce to a low simmer. Cover with a lid and cook without stirring for 10 minutes. Remove from the heat and set aside, covered, for another 10 minutes.
Place the rice in a large bowl. Pour the vinegar seasoning over the rice and mix the seasoning through the rice. Continue turning the rice for a couple of minutes. Cover with a damp cloth and leave to cool to room temperature before serving.
Peel the cucumber and remove the seeds. Cut the flesh into strips and then into small dice. Remove the skin and any pin bones from the salmon, sea bass and tuna. Cut the fish into strips and then into small dice the same size as the cucumber. Mix together the rice wine vinegar, sugar and salt. Combine this dressing with the fish and the cucumber and leave to marinate for 15 minutes.
Cut the nori sheets into strips 2 to 3cm wide. Roll a small smount of rice into a ball then press it down to create a flat oval shape approximately 1cm high. Repeat this process until you have used all of the rice. Wrap a strip of nori around each oval of rice, making sure the shiny side is facing outwards. Stick the ends together with a little water to secure the nori. You should be left with a gap of about 1cm on top of the rice. Place a small amount of wasabi on top of the rice then fill the gap with the fish and cucumber mixture.
«Vary the fish in this recipe according to taste. Prawns or crab work very well too.»