Clock genes and circadian rhythmicity in juvenile Atlantic salmon in response to light conditions

Abstract

The manipulation of biological timekeeping through the modification of light environment is widely used in aquaculture to stimulate desirable physiological responses in Atlantic salmon at key developmental stages. However, the understanding of the intricate interactions between light conditions, the circadian mechanism, and the control of downstream outputs in the species remains largely unknown. In this research, the effects of light condition on the expression of clock genes in Atlantic salmon were investigated at key freshwater life stages, early development and parr. This was achieved by identifying the effect of whole genome duplication on clock genes. Family members were identified and classified, detailing the enhanced number of clock genes present in Atlantic salmon in relation to the latest common ancestors and other salmonids. Comparison of gene expression profiles across multiple light conditions identified evidence of altered clock gene expression under different photo cue, light intensity, and spectral composition. Photo cue was the most influential light condition. Exploring the effect of developmental stage, the milestone of first feeding was key in the entrainment of the circadian clock. Displaying a significant increase in the number of clock genes which were rhythmically and cyclically expressed after the event, in keeping with the number of entrained genes identified in parr. Overall, this research provides fundamental insight into the significance of key early developmental stages and the effects of light conditions on clock gene expression in Atlantic salmon.