Histological Changes in the Organs and Tissues of Migrating and Spawning Pacific Salmon (Genus Oncorhynchus)1

A histological study was made of the various organs and tissues of the Pacific salmon at successive stages of sexual maturation from the sea to the spawning grounds. Pronounced changes were found in the body structures of the spawning salmon prior to death. These consisted principally of degeneration with or without atrophy as shown by the stomach, liver, spleen, thymus, thy-roid, gonads, pituitary, kidney and cardiovascular system. On the contrary, certain organs exhibited hypertrophy and hyperplasia, e.g., adrenal, pancreatic islets and skin. The inception of some of the above changes was detected several months before full sexual maturity. Comparison with the histological altera-tions occurring in Cushing’s syndrome, experimental hyperadrenocorticism and aging, suggested that many of the tissue changes found in the salmon could be ascribed to the effects of hyperactivity of the adrenal gland. Previous finding of high concentrations of 17-OHCS in the plasma of spawning salmon lends sup-port to this inference.