Phospholipids (PL) are localized in biological membranes. So the decomposition of PL might result in the disintegration of subcells in fish muscle. Thereore, in order to study an alteration of biological membranes caused by the PL decomposition in frozen fish, carp ordinarymuscle was stored at -℃, because the most rapid rate of enzymatic hydrolysis of PL has been observed at -5℃ in the range from 0 to -20℃, and the muscle was periodically taken out and observed by freeze-etching (F-E) electron microscopy. Sarcoplasmic reticulum (SR) was principal subcell in carp ordinary muscle immediately after death, and mitochondrion or other subcells were scarcely observed except transverse tubules. This indicated that PL were localized predominantly in SR. So the change of SR was observed during storage of carp ordinary muscle at -5℃. The frequency of occurrence of cross sections of SR in F-E images increased only by freezing of the ordinary muscle, and then increased further up to 30 days. The F-E images of ordinary muscle after storage for 22 days showed little difference as compared with that immediately after death. But after 30 days, the area of SR began to decrease, and the irregular distribution of particles was also observed in some fracture faces of SR. After 90 days, few normal fracture faces of SR were observed.
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