Onset of circadian rhythmicity in the brain of Atlantic salmon is linked to exogenous feeding.

An organism's biological processes are adapted to and driven by rhythmicity in the natural environment and periodicity of light is one of the most influential factors. In a developing organism, the onset of circadian rhythmicity might indicate the time point of functional necessity for aligning processes to the environment. Here, the circadian clock mechanism has been studied in the developing brain of Atlantic salmon (Salmo salar), by comparing the endogenous feeding alevin, independent on the environment for nutritional supply, to the exogenous feeding fry, dependent on the light period for detecting and catching prey.

Photoreception and transcriptomic response to light during early development of a teleost with a life cycle tightly controlled by seasonal changes in photoperiod.

Light cues vary along the axis of periodicity, intensity and spectrum and perception of light is dependent on the photoreceptive capacity encoded within the genome and the opsins expressed. A global approach was taken to analyze the photoreceptive capacity and the effect of differing light conditions on a developing teleost prior to first feeding. The transcriptomes of embryos and alevins of Atlantic salmon (Salmo salar) exposed to different light conditions were analyzed, including a developmental series and a circadian profile.

Rhythmic Clock Gene Expression in Atlantic Salmon Parr Brain.

To better understand the complexity of clock genes in salmonids, a taxon with an additional whole genome duplication, an analysis was performed to identify and classify gene family members (, and ). The majority of clock genes, in zebrafish and Northern pike, appeared to be duplicated. In comparison to the 29 clock genes described in zebrafish, 48 clock genes were discovered in salmonid species.