The Toyama pressed sushi made with trout and wrapped in bamboo leaves is masuzushi.
Masuzushi is a regional specialty of Toyama Prefecture and a type of oshizushi, or pressed sushi. Vinegared trout is laid over vinegared rice, then the rice and fish are wrapped in bamboo leaves. A heavy weight compresses the bundle for several hours, helping shape the sushi and develop its flavor.
The finished dish is traditionally packed in a round bentwood container called a mage-wappa and is widely sold as an ekiben, or boxed meal associated with railway travel. Masuzushi is often confused with other regional leaf-wrapped or pressed sushi, but its defining combination is Toyama, trout, bamboo leaves, and pressing. Sasazushi is a different regional preparation, while kabura-zushi uses turnip and fish.