Since salmon spend part of their lives in freshwater, they often carry tapeworms. For the larvae to be killed, the fish must be cooked or frozen at minus−31 °F (−35 °C) or colder for 15 hours. "Sushi grade" is a marketing term, not enforced by the FDA in the US(although the FDA does recommend that fish should be frozen before it's eaten raw). Make sure that the salmon you are buying has been frozen properly and recently. Tell the person from whom you are buying the fish that you intend to eat it raw. If there is a Japanese market in your area, try going there. Buy the fish on the same day you are preparing the nigiri.;
, You cannot just use any rice; the rice needs to stick together so it can be picked up with chopsticks. Plus, sushi rice is seasoned with vinegar (the "su" in "sushi" actually means vinegar), sugar, and salt.
 The pieces should be approximately 5cm (2") long, 3 centimeter (1.2 in) (1") wide, and 1⁄2 or 1 centimeter (0.2 or 0.4 in) (less than 1/2") thick. If the fillet isn't thick enough to get the width you're looking for, slice diagonally. A very sharp knife is recommended here.
 Take a small amount of rice (about 3/4 the size of your palm). Roll and squeeze it together until it rolls into a firm "log" sized rectangle.
 The wasabi is optional, but it helps the salmon stick to the rice, and adds a touch of extra flavor. Place the fish on the rice "log", with the wasabi side on the rice.
 Serve.
Get the freshest, safest salmon you can find.
Make Sushi Rice.
Slice the salmon into pieces.
Dip your fingers into water and scoop up a little amount of rice.
Smear a pea-sized dab of wasabi on one side of the fish slice.
Gently shape the rice and salmon together.
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