Thirty years ago, I had a friend who asked for some immigration help. He was a ‘fish handler’ who was stationed in eastern America in order to live on fishing vessels to control the fish at the time they were hooked on the line.
He spoke of the importance of Kizu, a scratch and the onset of biological problems as a result of bad handling practices. Physical appearance and damage caused by external factors such as harpoon damage, shark bite, hook damage, line marks are undesirable. These imperfections affect the price of the tuna and certainly the price. Careful handling and the use of wet, shock absorbing matting and accurate use of the gaff or harpoon is critical in order to preserve the fish’s integrity.
The result of bad handling is that the color of the meat will turn opaque (referred to as Yake) with varying states of color from pale reddish pink to darkish grey and the meat texture will lose its tenderness. Without insufficient cooling of the fish immediately after killing, you are going to lose the tuna’s price. Many things can when ﬁsh are extremely vigorous at capture, heating his body and building up lactic acid.
The key is to minimize the amount of thrashing or movement of the ﬁsh once on the deck to prevent lactic acid build up. Possible to reduce onset of yake by allowing a vigorous ﬁsh time to ‘recover’ prior to killing and chilling rapidly after killing. The handler must cover the eyes and kill by ikijimi (spiking) with a sudden action.