for the use of , a particular locally differentiated variety of wild goldfish endemic to Lake Biwa. consists of an oblong mound of sushi rice that a chef typically presses between the palms of the hands to form an oval-shaped ball and a topping (the ) draped over the ball. It is usually served with a bit of wasabi; toppings are typically fish such as salmon, tuna, or other seafood. Certain toppings are typically bound to the rice with a thin strip of nori, most commonly octopus (), freshwater eel (), sea eel (), squid (), and sweet egg (). is a special type of : an oval, hand-formed clump of sushi rice that has a strip of nori wrapped around its perimeter to form a vessel that is filled with some soft, loose or fine-chopped ingredient that requires the confinement of nori such as roe, , oysters, (sea urchin roe), sweetcorn with mayonnaise, scallops, and quail eggs. was invented at the restaurant in 1941; its invention significantly expanded the repertoire of soft toppings used in sushi. is a style of sushi made by pressing rice and fish into a ball-shaped form by hand using a plastic wrap. , also known as , is a pressed sushi from the Kansai region, a favorite and specialty of Osaka. A block-shaped piece is formed using a wooden mold, called an . The chef lines the bottom of the with the toppings, covers them with sushi rice, and then presses the mold's lid to create a compact, rectilinear block. The block is removed from the mold and then cut into bite-sized pieces. Particularly famous is or . In , all the ingredients are either cooked or cured, and raw fish is never used. Oshizushi wrapped in persimmon leaves, a specialty of Nara, is known as . Western-style sushi The increasing popularity of sushi worldwide has resulted in variations typically found in the Western world but rarely in Japan. A notable exception to this is the use of salmon. The Japanese have eaten salmon since prehistory; however, caught salmon in nature often contains parasites and must be cooked or cured for its lean meat to be edible. On the other side of the world, in the 1960s and 1970s, Norwegian entrepreneurs started experimenting with aquaculture farming. The big breakthrough was when they figured out how to raise salmon in net pens in the sea.