Britannica Sources used in this answer

What role does thyroxine play in salmon imprinting?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A herd of wildebeest, including calves, moves across a dusty savanna in Africa with scattered trees visible in the background. — Migration A herd of common wildebeest (*Connochaetes taurinus*) migrating across a dusty savanna in Africa. The animal is a keystone species (i.e., a species with a disproportionately large effect on its biological community) in plains and acacia savanna ecosystems from southeastern Africa to central Kenya.

In the context of salmon migration, thyroxine—a thyroid hormone—plays a critical role in the timing of imprinting.1

During the early stages of a salmon's life, an increase in thyroxine activity coincides with the period when the fish imprints on the specific chemical signature of its home stream. It is presumed that this hormonal activity induces physiological changes in the sensory cells of the olfactory epithelium, allowing the fish to learn and store environmental odors.1

The levels of thyroxine in the blood are influenced by both the age of the fish and environmental conditions, which explains why the timing of imprinting can vary across different locations. While thyroxine facilitates the initial imprinting process, the subsequent increase in olfactory sensitivity required for the salmon to recognize these odors during its return journey is regulated by reproductive hormones.1