Impact of lighting conditions on the developmental physiology of Atlantic salmon (Salmo salar)

The Atlantic salmon (Salmo salar) lifecycle is punctuated by distinct ontogenic stages which are routinely manipulated commercially by photoperiod regimes to enable year-round production. As such, light plays a critical role throughout the production cycle, however, it remains poorly characterised and light spectrum and intensity have not been defined optimally yet. This thesis was therefore set out to test the effects of narrow bandwidth light (Blue-λ(max) 444 nm, Green-λ(max) 523 nm, Red-λ(max) 632 nm and White) and intensity in freshwater (FW). Fry-parr development, out-of-season smoltification and ocular and vertebral health were examined as was the long-term effects of FW light regimes on seawater (SW) growth and muscle structure. In addition, the impact of photoperiod regimes on out-of-season smolts following transfer to SW was investigated. Major findings from the trials conducted show that light spectrum and intensity influence parr development with lower intensities performing better than higher intensities. Both the initiation and duration of smoltification was impacted by spectrum. Importantly, this doctoral work showed that daily changes in light intensity, from low during the scotophase to high during the photophase applied for the duration of a standard out-of-season smoltification regime was capable of providing a sufficient cue for the induction of smoltification. Historic FW light exposure impacted SW performance and post-transfer SW photoperiod had significant impact upon growth and maturation development. Results based on changes to the gonadosomatic index provide important guidance for suitable post-transfer photoperiods for smolt transferred to SW around the winter solstice. Importantly, from the parameters tested, exposure to different spectrum or light intensities did not adversely affect vertebral or ocular health. This thesis did not only focus on the physiological effects of light but also aimed to characterise better the pathways involved in light perception and integration. To do so, the neural response to both broad spectrum white light, darkness and Red and Blue light was investigated through deep brain insitu-hybridisation and high throughput sequencing (NGS) of the pituitary gland. Results showed substantial spectral and light/ dark changes in the both the deep brain and pituitary transcriptome. Overall, this research provides both scientifically interesting and commercially relevant guidance for the optimisation of lighting systems for use in captive salmon aquaculture.Major findings from the trials conducted show that light spectrum and intensity influence parr development with lower intensities performing better than higher intensities. Both the initiation and duration of smoltification was impacted by spectrum. Importantly, this doctoral work showed that daily changes in light intensity, from low during the scotophase to high during the photophase applied for the duration of a standard out-of-season smoltification regime was capable of providing a sufficient cue for the induction of smoltification. Historic FW light exposure impacted SW performance and post-transfer SW photoperiod had significant impact upon growth and maturation development. Results based on changes to the gonadosomatic index provide important guidance for suitable post-transfer photoperiods for smolt transferred to SW around the winter solstice. Importantly, from the parameters tested, exposure to different spectrum or light intensities did not adversely affect vertebral or ocular health. This thesis did not only focus on the physiological effects of light but also aimed to characterise better the pathways involved in light perception and integration. To do so, the neural response to both broad spectrum white light, darkness and Red and Blue light was investigated through deep brain insitu-hybridisation and high throughput sequencing (NGS) of the pituitary gland. Results showed substantial spectral and light/ dark changes in the both the deep brain and pituitary transcriptome. Overall, this research provides both scientifically interesting and commercially relevant guidance for the optimisation of lighting systems for use in captive salmon aquaculture