Influence of death struggle on the structural changes in chub mackerel muscle during chilled storage

Chub mackerel (34-35 cm, approximately 500 g), which were caught by fishing with a rod and line at the Bungo Channel, Oita prefecture, were rested ove rnight in a fish preserve and either killed by decapitation (control group) or allowed to struggle in air for 30 min (struggled group). Muscle samples were excised every 4 h, and measurements on breaking strength and histolog ical observations were done for both groups. The breaking strength of muscl e in the control group was significantly higher than that in the struggled group, whereby a decrease in breaking strength was delayed for 12 h compare d to the struggled group. Light microscopy showed space extension among mus cle cells in association with a decrease in breaking strength. Especially i n the struggled group, the extended area was larger and the difference in a rea was significant at the time when breaking strength showed a significant difference. Using electron microscopy, the extended area showed cut and/or disappeared collagen fibrils. From these results, it was demonstrated that struggling to death promoted the degradation of collagen fibrils and the w eakening of connective tissue and, resultantly, led to the faster softening of muscle of chub mackerel.