The effect of narrow banded LED light on development and growth performance

In this project, we have investigated the effect of various light qualities and light rhythms on early developmental stages of Atlantic salmon. Light is known to influence several biological processes in fish, and the project has described early light perception and the effect of light on early development and growth. We have identified around 40 nonvisual opsins in salmon and mapped their location in the brain and eye. Our histological maps of the salmon brain show an advanced nonvisual photoreceptive system early in development. In the project, we have done RNA sequencing of 102 embryos and larvae that are developed under different light qualities and light rhythms. The aim of the project has been to gain a basic understanding of the photosensory systems in salmon and understand how light influences early development by influencing regulatory networks, including muscle development. By focusing on the stage before first feeding, while the larva still consumes the yolk sack, we have avoided any feeding effects. Since salmon is highly developed at this stage, the large RNAseq matrix represents a global approach to gene activity analyses, which are also relevant to older stages. A 24-hour sampling of the different light qualities has been performed and data from this material show how gene expression is affected throughout the day at different periods, intensity and spectres. Our results reveal that it is a great difference in gene activity in the larvae exposed to different light periods and spectrums. In the project, the long-term effect of early light exposure was studied by stimulating embryos and larvae for different periods up to first feeding, followed by incubation in equally light conditions from first feeding to post-smolt. Analyzes of muscle growth show that early light rhythm influences muscle fiber composition in the juvenile stage, in that the large fibers are smaller, which gives a significantly higher fiber density. The project has collaborated with commercial partners to gain insight into how one can use light on early stages to improve development and growth in the aquaculture industry.

The project results have enlightened the knowledge of the photoreceptive system in Atlantic salmon and shown how light influences early development by light stimulation studies. By employing RNA sequencing in the project, the practice and policy of the project participants have evolved. Knowledge acquired on photoreception, light stimulation studies and RNA seq is now implemented in new projects. The RNA seq results will be available in the European Nucleotide Archive so that results are available for other users. The project has had several international partners including a joint PhD candidate at the University of Stirling, strengthening the collaboration between projects participants in the field of aquaculture, fish physiology and chronobiology. Commercial partners have also been involved in the project and the insight into how light stimulation at early developmental stages affects development and growth will be applied to the aquaculture industry and producers of LED technology.

In this project we will investigate the effect of narrow banded LED light exposure during the early developmental stages of Atlantic salmon. The exposure will be done at a stage where the common practise today is to keep the eggs in darkness. Light is known to influence the cell cycle progression in teleosts and the project will examine photoreception and the effect light has on generation of progenitors in muscle development and the subsequent potential for increased growth performance. Our preliminary studies, using light manipulation show that narrow banded LED light activates neurons in the salmon brain in regions of deep brain photoreceptors. The nonvisual photoreceptor systems seem to be the first light detectors that are functional at embryonic stages. Studies in zebrafish have shown that the cell cycle is light regulated, even in tissue cultures. Recent studies show that temperature manipulation during a short window in embryogenesis is enough to affect adult myogenic phenotype. Our main objective will be to gain fundamental knowledge on the early photo sensory systems in salmon and understand how light influences early development, muscle progenitor cells, myogenesis and subsequent impact on muscle growth. Since light is a strong cell cycle regulator in teleosts we will use light of different spectres, intensities and period to try to influence establishment and proliferation of muscle progenitor cells and myogenesis. Using the salmon genome annotation, transcriptome sequencing and bioinformatics we will do system biology of light manipulated embryos in order to characterize photo driven processes and myogenesis. Long term effects of early light manipulation with optimized spectres and intensities will be analysed in relation to growth performance and muscle fibre analysis in a commercial salmon farm. This project will provide new insights into how light can be use on early developmental stages of salmon to improve muscular growth in salmon production