Lunar Phasing of the Thyroxine Surge Preparatory to Seaward Migration of Salmonid Fish

Abstract

Anadromous salmonid fish show a distinct surge in plasma thyroxine during the smoltification period prior to their migration to the sea. Analysis of 27 groups of hatchery-reared salmon and anadromous trout indicates that thyroxine levels peak coincident with the new moon. The ability to predict migratory readiness by lunar calendar would have substantial implications for the efficient culture of this economically important protein resource.