Discovery explains how salmon read seasons, with aquaculture implications.
Researchers led by the University of Massachusetts Amherst report that Atlantic salmon pituitary glands contain photoreceptors that directly sense daylength, triggering hormonal changes linked to seasonal behaviours such as smoltification and migration. The findings, published in Proceedings of the Royal Society B, show that exposing isolated pituitary tissue to longer daylight increased thyroid-stimulating hormone, initiating the T4-to-T3 pathway associated with seasonal transitions.
The work, conducted with collaborators from the University of Tokyo, Toho University and the University of Gothenburg, suggests that 7–9% of ambient light can penetrate the skull and reach the pituitary, allowing a direct photoperiod response independent of the eyes. The authors say this mechanism helps explain how salmon time spring migrations and other life-history events.
For aquaculture, the study points to potential refinements in photoperiod management to improve the timing and consistency of smolt development, growth and seawater transfer. The researchers note that climate change may decouple environmental conditions from daylength cues, increasing the value of precise light-control strategies in hatcheries and grow-out systems.
