Rinse the rice in a sieve under cold running water until it is clear. Drain well.
Add the water and rice to a pan and leave to absorb for approx. 30 mins. Bring to the boil with the lid off, reduce the heat until the water has evaporated, leaving small indentations on the surface of the rice, cover and leave to absorb over a low heat for approx. 10 mins, do not lift the lid.
Warm the sugar, rice vinegar and salt in a small pan, stirring until the sugar has dissolved. Transfer the rice to a wide-bottomed bowl, drizzle the warm liquid on top, mix carefully with a fork for approx. 3 mins. while fanning. Cover the rice with a damp cloth and leave to stand for approx. 15 mins.
Place each nori sheet on a bamboo mat or piece of cling film with the rough side facing up. Place 1/3 of the rice onto each sheet, leaving a gap of approx. 2 cm at the top. Flip the nori sheet and rice.
Mix the egg, soy sauce and sugar. Heat the oil in a small non-stick frying pan. Pour in the egg mixture, cook over a medium heat, cut in half and place on top of each other, leave to cool, cut into strips approx. 1 cm thick.
Place 1/3 of the avocado, cream cheese and sturgeon lengthwise down the middle of each nori sheet.
Roll up the filled nori sheets, roll them between your hands until everything holds together. Fill the ends of the rolls with rice, press firmly. Slice the rolls into 8 equal pieces using a very sharp, wet knife.