I was sitting with the other day and talking about Japanese fish with the executive chef of a well-known resort in Phuket. He touched on a topic close to my heart, the importance long-line fishing and rigor mortis. This subject is more complex but on the surface it seems straight forward. To keep it simple, there are three basic principles or clarifications of rigor mortis in the Japanese fishing industry and they are: Iki, Shime, Sengyo.
The highest quality fresh fish are produced from live fish by using the iki-jime method, a method of stunning the fish with a spike, and are termed “iki fish”. This term is reserved for fish which are determined to be still in the pre rigor mortis stage, in other words, the fish is brain-dead but muscle tissue is still alive with enzymatic activities. The fish which are spiked by the iki-jime method and immediately treated on board the fishing vessel and by using ice slurry, may have their rigor mortis prolonged for up to three to seven days.
For those fishermen who cannot supply iki fish, they are forced to supply rigor mortis stage “shime” fish. The shime fish are those spiked with the iki-jime treatment but offered at market already in a stage of rigor mortis. These are the fish that are being exported for sushi grade to other countries.
It is common for iki fish to arrive at market in the stiff “shime stage” and consequently unable to command the best price. However, it should be realised that they are still iki-jime fish and therefore can command a better price than those fish in which rigor mortis has set in but which have not been spiked, bled or slurried at the fishing grounds.
Lastly the Sengyo are the most undesirable and are post rigor mortis.