Chub mackerel from the Bungo Channel, Oita Prefecture, Japan, receives a high market price. This high price is due to the tough texture that is not present in chub mackerel sold in public markets. The purpose of the present study was to resolve the effect of an inhabited sea area (the area where the a fish population lives: Bungo Channel or Kumanonada sea in the present paper) on meat firmness and the post-mortem change in chub mackerel during chilled storage. Chub mackerel were obtained alive from the Kumanonada sea in Mie Prefecture, Japan, in March 2000. They were killed instantly by decapitation as were those collected from the Bungo Channel in Oita Prefecture. Dorsal muscle was collected every 4h and measurements of its breaking strength and histological observation of its structure were carried out. The breaking strength of chub mackerel from the Kumanonada sea was lower than that of the chub mackerel from the Bungo Channel. In contrast, the softening rate of meat was almost the same after 16-20 h storage. Using light microscopy, separation between muscle cells was observed from 4h after death, suggesting weakening of the endomysium. Additionally, transmission electron microscopy showed that collagen fibrils existing near muscle cells tended to disintegrate predominantly. According to these results, it was clarified that chub mackerel from the Bungo Channel has tougher meat than that from the Kumanonada sea, and the difference in meat texture was speculated to be due to the difference in exercise intensity between these two sea areas.

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