Rinse the rice under running water until clear. Drain for 1 hour. In a saucepan with 1 litre of boiling water, cover and cook for 2 minutes over a high heat, then for 5 minutes over a medium heat. Finally, cook for a further 15 minutes over a low heat. When the rice is cooked, cover the pan with a cloth and replace the lid. Leave to rest for 15 minutes.
Spread the rice evenly in a long dish. In a bowl, mix the rice vinegar, sugar and salt. Stir until the sugar has dissolved completely. Sprinkle over the rice. Leave to cool.
Season the fillet of sea bream with salt and leave to stand for 1 hour. Place in a dish, sprinkle with vinegar and marinate for 30 minutes. Put the fillet on a spit and grill on the skin side until golden. Cut 4 thick slices. Also cut 4 slices from the salmon fillet.
Place a slice of fish in the palm of your hand, add a dab of wasabi mayonnaise and 2 spoonfuls of rice.
Make rectangles 6 cm long, folding the edges of the slice over the rice.