Discrimination of muscle fiber types in ordinary muscle by actomyosin ATPase activity and its comparison among various fishes and muscle parts

As part of study on the relationship between muscle fiber types and rigor m ortis progress in dorsal ordinary muscle of fish, the histochemical discrim ination of muscle fiber types in dorsal ordinary muscle was examined by the acid and alkaline stabilities of actomyosin ATPase activity, and a compari son was carried out among various fishes and parts. The optimum combination of pH and time for acid preincubation was remarkably different within the ranges from pH 4.48 to pH 4.54 and from 0.5 min to 4.0 min among ten sample fishes, while that at alkaline preincubation was almost similar at pH 10.4 0 although the time slightly differed. In any case, the muscle fiber types in dorsal ordinary muscle of various fishes were discriminated by the acid and alkaline stabilities of actomyosin ATPase activity. The four kinds of m uscle type were identified in ten sample fishes and these muscle types were only the IIa like subtype of white muscle in one fish, the IIa and IIb lik e subtypes of white muscle in two fishes, the pink muscle and IIa or IIb li ke subtype of white muscle in two fishes, and the pink muscle and IIa and I Ib like subtypes of white muscle in six other fishes, respectively. Further more, the muscle fiber types in dorsal ordinary muscle were remarkably diff erent between wild and cultured fish, among specimens of the same fish, and among parts along the body length and at varying depths.