The ingredients used inside sushi are called "gu", and are, typically, varieties of fish. For culinary, sanitary, and aesthetic reasons, the minimum quality and freshness of fish to be eaten raw must be superior to that of fish which is to be cooked. Sushi chefs are trained to recognize important attributes, including smell, color, firmness, and freedom from parasites that may go undetected in commercial inspection. Commonly used fish are tuna ("maguro, shiro-maguro"), Japanese amberjack, yellowtail ("hamachi"), snapper ("kurodai"), mackerel ("saba"), and salmon ("sake"). The most valued sushi ingredient is "toro," the fatty cut of the fish. This comes in a variety of "ōtoro" (often from the bluefin species of tuna) and "chūtoro", meaning "middle toro", implying that it is halfway into the fattiness between "toro" and the regular cut. "Aburi" style refers to "nigiri" sushi where the fish is partially grilled (topside) and partially raw. Most nigiri sushi will have completely raw toppings, called "neta".