WORLDWIDE: The fish are guided to platforms by divers for harvesting. They are euthanised humanely, by an immediate spike into their brain. This method is known as “iki jime” in Japanese. It is a technique that minimises stress as lactic acid in their system that can change their flavour. It takes approximately 40 seconds to get the fish into an ice slurry or refrigerated sea water, which keeps quality at a premium. On board the tuna harvest boats are representatives of Japanese companies who scrutinise the product before export. They look for good shaped fish that have suffered no damage in the harvesting process. A segment is taken from the tail to determine quality. A strong, deep red colour and good fat deposits are considered extremely favourable.
Quality and colour of SBT muscle flesh is assessed 3 times prior to the sale of a fish. Tuna may be purchased frozen or fresh.
Tuna Filleting or Loining
There are many parts to the perfect fish – the prized toro or belly section, akami along the backbone and the kama or neck area. Japanese chef Yumiko Asao cuts at an angle along the grain, using the toro and the jewel like akami sections of the fish for juicy, melting pieces of Australian sashimi.
Southern Bluefin Tuna will be in the markets in Japan within 48 hours of harvesting and processing.
Source: https://asbtia.com.au/tuna-products/tuna-processing