Changes in plasma calcitonin and calcium during the migration of salmon.

The levels of immunoassayable calcitonin and of calcium were measured in the preblood of sockeye salmon during their migration from sea water to fresh water to spawn. Plasma calcitonin was higher in the females than in the males during all stages of migration as was plasma calcium except during spawning. In both sexes calcium decreased progressively throughout migration. In the male, calcitonin decreased as the fish arrived in fresh water but increased again at the spawning. These observations suggest that calcitonin may play an important role in the reproductive cycle of fish.