Question: Why is sushi fish of higher quality?
About the article "Sushi", section "Neta".

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The most remarkable feature of conveyor belt sushi is the stream of plates winding through the restaurant typically in a clockwise rotation to make it easier to grab the plate as it passes by.
The selection is usually not limited to sushi; it may also include drinks in Tetra Paks, fruits, desserts, soups, and other foods.
Beer can be ordered from the attendants, often served with an empty plate to keep track of the bill.
Busy sushi restaurants serve the best quality, as the sushi gets eaten faster and does not get dry while rotating for a long time.
Some restaurants have RFID tags or other systems in place to remove sushi that has rotated for too long.
Some inexpensive conveyor belt sushi restaurants may imitate an expensive dish using less expensive ingredients.
For example, they may replace chopped fatty tuna belly meat with other fish meat.
Some larger chains can keep down costs for quality food by ordering in large amounts. 
Sushi can be prepared with either brown or white rice.
Sushi is often prepared with raw seafood, but some common varieties of sushi use cooked ingredients.
Raw fish (or occasionally meat) sliced and served "without rice" is called "sashimi".
Sushi is often served with shredded ginger, wasabi, and soy sauce.
Popular garnishes are often made using daikon. 
Feng Sushi is a UK-based restaurant chain known for advocating sustainable fish farming.
The company was founded in 1999 by chef Silla Bjerrum and chef Jeremy Rose, with restaurant entrepreneur Luke Johnson the majority owner since 2010.
Feng Sushi was the first restaurant in the UK to offer sushi for delivery.
Bjerrum has been credited by Caterer and Hotelkeeper Magazine as being "...part of the movement that brought sushi to the mainstream". 
Sushi can be paired with a variety of whiskies, but "Whisky Magazine" found Talisker came out on top in testing.
Ardbeg is also recommended, due to its salty, briny quality. 
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 be completely raw.
Other seafoods such as squid ("ika"), eel ("anago" and "unagi"), pike conger ("hamo"), octopus ("tako"), shrimp ("ebi" and "amaebi"), clam ("mirugai", "aoyagi" and "akagai"), fish roe ("ikura", "masago", "kazunoko" and "tobiko"), sea urchin ("uni"), crab ("kani"), and various kinds of shellfish (abalone, prawn, scallop) are the most popular seafoods in sushi.
Oysters, however, are less common, as the taste is not thought to go well with the rice.
"Kani kama", or imitation crab stick, is commonly substituted for real crab, most notably in California rolls.
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.
Tofu and eggs (in the form of slightly sweet, layered omelette called "tamagoyaki" and raw quail eggs ride as a "gunkan-maki" topping) are common.