Protein degradation and protease activity of chum salmon (Oncorhynchus keta) muscle during spawning migration

Sarcoplasmic protein content decreased significantly and myosin heavy chain was degraded gradually during spawning migration of chum salmon (Oncorhynchus keta). Acid and neutral proteinase activities increased significantly during spawning migration. These proteinase activities were higher in females than in males. High levels of acid proteinase were not caused by the injury of lysosomal membranes. Considering the physiological states of chum salmon, neutral proteinase activity might be related to the degradation of muscle protein. As the changes in serum sex steroids were similar to those in the protease activities during spawning migration, it was considered that high levels of protease activity during spawning migration were closely related to the serum levels of androgens.