Why is sushi fish of higher quality ?
Pickled daikon radish ( " takuan " ) in " shinko maki " , pickled vegetables ( " tsukemono " ) , fermented soybeans ( " nattō " ) in " nattō maki " , avocado , cucumber in " kappa maki " , asparagus , yam , pickled ume ( " umeboshi " ) , gourd ( " kanpyō " ) , burdock ( " gobo " ) , and sweet corn ( possibly mixed with mayonnaise ) are also used in sushi .