When it comes to processes, the Japanese are the most thorough and accurate and this is costly. When it comes to fish and tuna fish in particular, it isn’t just tuna in a can, it’s a tuna on a line, and this is taken to the nth degree.
Japanese trade tuna with more precision than diamond dealers trade diamonds. There are no certificates, no machines, or x-rays, just raw experience. The fish is either perfect or not, and precision in Japanese fishing has zero tolerance for error.
In most countries consumers misunderstand the reasons why tuna is so costly, and many think it’s just because of Japanese consumption. In fact, the degree of expertise it takes to catch a tuna, or the importance in handling and preparing it for shipment is key.
The “after catch” is the most important time when it comes to quality and freshness, sashimi grade fish cannot be mishandled. A fisherman without thinking about what to do after the fish is caught, is like a long distance runner with one leg.
Here are the terms used in Japan for grading and judging tuna by professionals in Tsukijii;
Kizu: a cut or scratch.
Morikizu: a harpoon or gaff damage.
Samekui: a shark bite.
Jyukon: a bullet wound may be a biological problem or consequence of bad handling practices. Physical appearance damage caused by external factors such as harpoon damage, shark bite, hook damage, line marks etc. Careful handling is always required and use of wet, shock absorbing mat and accurate use of the gaff or harpoon is necessary or damages is caused.
Yake & Shinyake: is all sections of the fish and shinyake is the core meat only. It could be a biological problem or consequence of bad handling practices when the colour of the meat turns opaque with varying states of colour; from pale reddish pink to darkish grey and the meat texture will lose its tenderness. This is caused by insufficient cooling of the fish immediately after killing and often happens to larger fish. It can also occur when fish are extremely vigorous at capture, heating their bodies and building up lactic acid. The object is to minimize the amount of thrashing, or movement of the ﬁsh once on the deck to prevent lactic acid build up. Possibly to reduce the onset of Yake by allowing a vigorous fish time to ‘recover’ prior to killing and chilling rapidly after killing. It is necessary to cover the eyes and kill by ike jime quickly to avoid any shock to the fish and delay rigour mortis.
Aotan: a dull blue/grey/green colour just under skin. Often seen on tail cuts and is particularly evident. It can occur as fish ages, or if the fish was dead on-line for some time and exposed to sun. This is all caused by bad handling. The haul line must be reeled in as possible to avoid fish being held on a line for extended periods in the sun, this is key.
Hara Go Aokunata: The is hen the stomach lining has changed from fresh, pink white colour to dull grey/blue. A key freshness indicator used by buyers to assess the value of a fish. This is caused by bad handling and to avoid it, you must process and handle as quickly as possible the fish, and not abruptly prior to chilling. Rapid chilling can be used and packing the gut cavity with ice when storing also helps maintain the fish’s freshness.
Henshoku Iro Warui: is when the meat colour turns very dark and can easily occur in tropical yellowfin, caused by bad handling.
Aozameta Iro Nashi: The meat colour is very light pinkish red. Caused by a lactic acid build up from vigorous movement of the fish. Usually caused by bad handling and can be minimized by controlling the amount of thrashing or movement of the fish during hauling and landing to prevent lactic acid build up.
Nijimi: the blood line (red muscle tissue) spreads into white meat and is caused by bad handling. Correct and complete bleeding of fish and correct chilling and storage is required. Blackish red spot spread around the meat can be from a direct result of the rupture of internal capillaries, causing bruising. This can be caused by dropping or knocking the ﬁsh during capture, while the fish is still alive, or incomplete bleeding. A mat is often used on the deck to prevent the fish from injuring itself. Always ensure the fish are bled completely prior to chilling.
Yamai: the generic term to describe damage caused by sickness of the ﬁsh. The flesh usually has a jelly like appearance and deteriorates over time but it is often hard to detect and internal sickness is not preventable.
Sashi Toroke & Azuki-Nagare: is when part of the body has degenerated. It could be a hole inside the meat or part of the body is empty. The cavity is a direct result of the melting of the meat. The damage is affiliated with a parasitic infection and is not detectable or preventable.
Rakkyo & Gari: the fish that have no fat and the flesh colour is dark red. Found in fish that have recently spawned or that have had insufficient feeding.
Hoshi,Goma & Azuki: a small hard white dots scattered throughout the body or in one section. This is caused by a parasite inside the body of the fish and is caused by a parasitic cyst that is not detectable or preventable.
Shirakumo: a cloudy white meat spread around the body, caused by sickness of the ﬁsh. A biological problem none. An internal sickness that is not detectable or preventable.
Konnyaku with or without Miware: the flesh colour is still red, but a dull, lacklustre red. The clarity of the flesh has changed to opaque. The meat will often look like beef. This can easily happen to larger ﬁsh when they lose fat. Can sometimes be identified in exceptionally skinny fish in the tail. Seasonal deterioration of the flesh can also result in Miware.