Increase in catheptic activity and appearance of phagocytes in the white muscle of chum salmon during spawning migration.

The mode of existence of cathepsins B and L in the white muscle of chum salmon was examined immunohistochemically with specific antibodies against cathepsins B and L. Cathepsins B and L were clearly demonstrated to be present in macrophage-like phagocytes near/in the muscle fibers in the white muscle. In particular, numerous phagocytes were observed around the necrotic muscle fibers. Therefore, the high cathepsin activity is considered to be brought about by the phagocytes appearing in the white muscle. It is probable that the phagocytes in the muscle are inferred to take such a part in the destruction of muscle fiber associates with the drastic physiological change such as sexual maturation and/or starvation of the fish during spawning migration.