Two-Toned Caviar Sushi

Sushi bars throughout Japan and America serve a wide variety of nigiri-zushi, which are compact ovals of rice on which a fresh slice of fish, such as tuna or fluke, is draped. Fish roes, which are also marvelous eaten with sushi rice, need a collar of paper-thin seaweed to keep them balanced atop the rice. This recipe makes colorful pairs of fish roe sushi—large red globes of salmon caviar and smaller crystalline globes of golden whitefish caviar. Both varieties