The fish pituitary directly responds to daylength and drives seasonality:

Seasonal timing is important for many critical life history events of organisms, and annual changes in daylength provide a reliable seasonal cue. In birds and mammals, photoperiod-driven seasonality is caused by changes in pituitary thyroid stimulating hormone (TSH), brain deiodinase (DIO) and triiodothyronine (T3), but it is unclear if a similar mechanism exists in fish. We used anadromous Atlantic salmon that migrate downstream and enter the ocean in spring to examine photoperiod signaling in fish. Manipulations of diurnal and circannual photoperiod cycles indicate that pituitary tshβb and brain dio2b transcription are long day signals that precede endocrine and physiological changes necessary for seawater entry. Exposure to long days caused increased dio2b transcription and T3 levels throughout the brain, and intracerebral T3 treatment resulted in elevated levels of plasma GH that drives migration physiology. Significant ambient light levels reach the pituitary, and transcription..., , # Data from: The fish pituitary directly responds to daylength and drives seasonality

Dataset DOI: [10.5061/dryad.8gtht7721](10.5061/dryad.5x69p8dds)

### Files and variables

#### File: Proc_Roy_Soc_London_B_all_data_final_d.xlsx

**Description:** Data from: The fish pituitary directly responds to daylength and drives seasonality

[https://doi.org/10.5061/dryad.8gtht7721](https://doi.org/10.5061/dryad.5x69p8dds)

## Description of the data and file structure

Data are from photoperiod and experimental manipulations of juvenile Atlantic salmon.

Each worksheet represents an experiment that is presented in a figure of the manuscript.

Each row is an individual salmon.

Each column is either a group (e.g. treatment, date) designation, or a parameter measured for that individual

### Worksheet descriptions:

Fig 1c-f Response of juvenile Atlantic salmon to natural photoperiod (LDN) and continuous short days (SD; LD8:16).

Fig 2a Time course of pituitary tshβb mRNA levels in fish under s...,