Light and Feeding Cues: Entraining Circadian Rhythms in Chinook Salmon Tissues

The circadian clock is known to help organisms synchronize their behaviour and physiology with the external environment. Present in almost all cells, the clock is made up of a transcription-translation feedback loop that is responsive to cues such as light and feeding. This clock functions to influence the timing of various processes within the cells by promoting gene expression at optimal timing. Chinook salmon (Oncorhynchus tshawytscha) is an important aquaculture species whose clock has not been characterized yet. The aim of the work presented here is to probe for the expression of circadian clock genes in some tissues of Chinook salmon. Since the clock is normally entrainable to light and feeding, manipulations of these two factors were carried out to explore the effects of this on the clock. Expression of clock genes is present in all tissues assayed (liver, heart, intestine, colon, retina, and skeletal muscle); however, the tissues differ in the phases of the daily rhythms, and some tissues do not display any rhythmicity. In the intestine, rhythmic daily expression is seen in various processes ranging from digestion to inflammation and cell regeneration. While it is still not conclusive whether the clock drives the rhythmicity seen in these processes, this serves as an indicator of possible circadian control. Overall, this thesis serves as a gateway to studying the role of the circadian clock in the life course of Chinook salmon, where it can be utilized to maximize growth in aquaculture and to uncover new facts about its life history in the wild