Influence of interposition of pink muscle fiber into dorsal ordinary muscle on increasing rate of K-value in various fish species
Twenty-seven fish species from the Sakishima Islands and Nagasaki living in water temperatures of 28 degreesC (12 fish species) and 17 degreesC (15 fish species), respectively, were used as sample fishes. Postmortem temporal changes of K-values were measured at 1-h intervals in the dorsal ordinary muscle of each fish, of which the remaining body was then kept in water at a controlled temperature of 32 degreesC. The increasing rate of K-value at 32 degreesC (DeltaK(32))was calculated from the regression line formed from the relationship between the kept time and the K-value. Muscle fiber types were differentiated by the stability of actomyosin ATPase preincubated in either acid or alkaline conditions. DeltaK(32) varied widely according to fish species, ranging from 0.98%/h to 14.00%/h. Although the mean value of each body of water was somewhat higher for fishes from Nagasaki at 17 degreesC than in fishes from Sakishima Islands at 28 degreesC, the difference was not significant. The interposition percentage of pink muscle fibers into the dorsal ordinary muscle was also distributed widely, ranging from 0% to 56.53% in number and from 0% to 53.68% in area. A significant correlation was recognized in the relationship between the number or area percentage of pink muscle fibers and deviation percentage of DeltaK(32) for all fish species sampled; r=0.411 (P<0.05) for number percentage and r=0.518 (P<0.01) for area percentage. These results suggest that the interposition of pink muscle fibers into the dorsal ordinary muscle might accelerate a temporal change of K-value in fish.