As part of a study to clarify the differences in the temporal change in K -value among fish species, the temporal change in K -value and the 5 ¢ -inosine monophosphate (5 ¢ -IMP) and pnitrophenol phosphate (p-NPP) degrading activities in the red, pink, and white muscle fibers in the dorsal muscle of the carp were compared. The temporal change in K -value was fastest in red, followed by pink, and white muscle fibers, at both 0 ∞ C and 32 ∞ C. Moreover, the 5 ¢ -IMP and p-NPP degrading activities were highest in red, followed by pink, and white muscle fibers at near optimum pH concentrations. The 5 ¢ -IMP degrading activity at pH 7.0 had a positive correlation with the increasing rate of K -value at 32 ∞ C for all types of muscle fibers. These results suggest that differences in increasing rates of K -values between red, pink, and white muscle fibers corresponded to the 5 ¢ -IMP degrading activities.KEY WORDS: 5 ¢ -inosine monophosphate degrading activity, carp, increasing rate of K-value, muscle fiber types, p-nitrophenol phosphate degrading activity.

To clarify the influence of the interposition of pink muscle fiber into dorsal ordinary muscle on temporal change of K‐value, using cultured carp, the dorsal muscle was divided into five muscle parts towards depth with the naked eye as follows: the dark muscle part (P‐1), the intermediate muscle part (P‐2) and three ordinary muscle parts (P‐3, P‐4, P‐5). These were organized from the muscle fiber types as follows: P‐1 was only red muscle fiber type. P‐2 was only pink muscle fiber type in a thin layer and two muscle fiber types of not only pink muscle fiber but also white muscle fiber of the IIa or IIb subtype in a mosaic pattern. All of P‐3, P‐4 and P‐5 were two muscle fiber types, white muscle fiber (IIa or IIb subtype) and pink muscle fiber. The temporal changes of K‐values were remarkably faster in the order of P‐1, P‐2, and three parts of P‐3, P‐4 and P‐5. The changes did not exhibit a remarkable difference among the three ordinary muscle parts. From these results, it was considered that the interposition of pink muscle fiber into the dorsal ordinary muscle might accelerate the temporal change of K‐value.