The main source of omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA) in our diet is supplied by fish, and an ever-increasing proportion of these are being produced by aquaculture. The drive for the growing market demand and production from sustainable sources has led to the use of high-energy (fat) diets and, recently, to the replacement of fishmeal and fish oil with non-marine components, such as plant meals and vegetable oils that are devoid of n-3 LC-PUFA. Both changes impact greatly on lipid and fatty acid metabolism in fish, with health implications for the fish and the human consumer. This impact highlights the need to investigate the basic molecular mechanisms underlying the regulation of lipid and fatty acid metabolism in fish, specifically focussing on the pathways of lipid homeostasis and LC-PUFA synthesis. The aim of this study was to develop and utilise Chinook salmon embryo (CHSE-214) cell line as a model for Atlantic salmon, Salmo salar L., to enable an integrated approach to study the biochemical and molecular regulation of lipid metabolism in fish. In particular, α-linolenic acid (LNA, 18:3n-3) and linoleic acid (LOA, 18:2n-6), which are essential fatty acids abundantly found in vegetable oils, and are precursors of LC-PUFA, were supplemented in combination with other fatty acids, to explore the effect of these on total lipid content, lipid class, FA composition and gene expression of CHSE-214 cell line. Total lipid content was extracted, followed by determination of lipid class and fatty acid analyses. Gene expression analyses of transcription/nuclear factors and various target genes in Atlantic salmon, including those involved in pathways of LC-PUFA synthesis and fatty acid oxidation, were carried out. The results demonstrated that CHSE-214 cell line, under experimental conditions, is able to convert LNA to eicosapentaenoic acid (EPA, 20:5n-3), and LOA to arachidonic acid (ARA, 20:4n-6), but not LNA and/or EPA to docosahexaenoic acid (DHA, 22:6n-3), highlighting the activity of elongase and desaturase enzymes during the conversion process. Changes occurring on the fatty acid profile and also at molecular level were observed. Understanding the role that transcription factors play in the regulation of lipid biosynthesis in fish will allow endogenous LC-PUFA synthesis to be optimised. The results from this study could be used to improve the efficiency of alternative, sustainable diets in aquaculture, while maintaining the nutritional quality of farmed fish for the final consumer. CHSE-214 cell line can therefore be used as a model to study the molecular mechanisms involved in the LC-PUFA biosynthesis, particularly in the conversion of LNA to EPA, which can then be reproduced in vivo, saving time and money.

At low doses, relevant to nuclear incidents and accidental releases of radioactivity, the detriment of radiation extends beyond direct effects. This thesis investigates genomic instability, a subclass of non-targeted effects where damage and lethality is transmitted vertically and expressed in the progeny of cells many generations after initial radiation exposure. Through a series of experiments using clonogenic assay of human and fish cell culture, studies described in this thesis describe lethal mutations, hyper radiosensitivity and increased radioresistance – processes involving repair mechanisms that dictate survival in cells exposed to low doses. Further study investigates the difference in the relative biological effect of alpha particle radiation compared to what is expected at high doses. Results demonstrate increased radioresistance in a human cell line while also revealing increased lethality in a fish cell line confirming the need for consideration of dose-dependence as well as variance in behaviors of different cell lines and species. It is hoped the conclusions of this thesis will inspire the creation of protocols with greater attention to the indirect consequences of exposure to radiation at doses relevant to nuclear incidents and accidents. / Thesis / Master of Science (MSc)