CHANGES IN THE FINE-STRUCTURE OF THE MYOCOMMATA-MUSCLE FIBER JUNCTIONRELATED TO GAPING IN RESTED AND EXERCISED MUSCLE FROM KING SALMON (ONCORHYNCHUS-TSHAWYTSCHA)

Fillets of king salmon (Oncorhynchus tshawytscha) were subjected to tw o defined levels of exercise and held for 0, 20, 40 or 120 h at 2 degr ees C followed by storage at -30 degrees C for 1 d or 6 weeks to exami ne their propensity for gaping. We followed the gaping process by obse rving the interface between the muscle fibres and myocommata with tran smission electron microscopy. The interface appeared as membrane-lined groove-like invaginations containing collagen fibres protruding into the muscle fibre bases. A successive loss of the lining from the invag inations, followed by the detachment of the sarcolemma/basal lamina co mplex from the muscle fibre base, was observed with increased storage and gaping. The primary determinant of gaping was the time in chill st orage before freezing. Increased time in frozen storage resulted in sl ightly more gaping. Under laboratory handling conditions, the exercise d fillets showed the same pattern of gaping as rested fillets when vie wed either pre- or post-rigor.