Influence of interposition of pink muscle fiber into dorsal ordinary muscle on 5'-IMP degrading activity in various fish species

: To clarify the cause of differences in the temporal change of K-value among fish species living in the same habitat water temperature, the influence of the interposition of pink muscle fibers into dorsal ordinary muscle on 5′-inosine monophosphate (5′-IMP) degrading activity was examined. Fourteen fish species from the Sakishima Islands (habitat water temperature 28°C) and from Nagasaki (habitat water temperature 17°C) were used for the sample fishes. Each of 5′-IMP and ρ-nitrophenol phosphate (ρ-NPP) degrading activities showed a peak at near pH 8.0 and near pH 5.0, respectively. These activities were somewhat higher in fish from Nagasaki than in fish from the Sakishima Islands. The interposition percentage of pink muscle fibers into dorsal ordinary muscle correlated significantly (P < 0.05) with the 5′-IMP degrading activity at pH 7.0. Furthermore, the activity at pH 7.0 correlated significantly (P < 0.001) with the increasing rate of K-value at 32°C (ΔK32). These results suggest that the difference in ΔK32 among fish species in the same habitat water temperature might be caused by differences in 5′-IMP degrading activity because of the differences in the interposition rates of pink muscle fibers into dorsal ordinary muscle.