Cod Lunacy, Hormonal Identification of Spawning Rhythms in Atlantic Cod Gadus Morhua

The reproductive strategies of many marine fishes rely heavily on the synchronization of gamete development and release. Lunar synchronisation of spawning is well documented in many tropical species though examples are rare in temperate waters. Here we explore the circulating levels of the primary sex steroids (11-ketotestosterone 17β-estradiol and testosterone) in both males and females of a newly captive population of Atlantic cod (Gadus morhua) throughout a full spawning season. The hypothesis that circulatory sex steroid concentrations are linked to lunar and semi-lunar cycles will be investigated using techniques from circular statistics and chronobology including cosinor analysis. This data provides a unique insight into the poorly understood spawning rhythms of an otherwise intensively studied marine species. Future work will build on these findings by assessing if/how the behaviour of cod spawning aggregations in the wild is influenced by differing lunar phases.