The utilisation and effects of early nutritional programming on Atlantic Salmon (Salmo salar. L)

Abstract

Atlantic salmon (Salmo salar) farming has traditionally relied upon the inclusion of omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA), especially eicosapentaenoic (EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3) acids, supplied from the finite marine ingredients, fish oil and fish meal. However, sustainable aquafeeds, primarily comprised from terrestrial origin sources as alternatives, lack n-3 LC-PUFA, which can potentially result in some adverse effects such as growth or health impairment as well as a decline in the nutritional value. Strategies such as nutritional programming, where fish are subjected to early feeding events that may result in effects in adult fish, aim to improve utilisation of sustainable aquafeeds based on epigenetics as its underlying mechanism.

This thesis investigated the application of nutritional programming in fingerlings at the freshwater phase (Chapter 4, 5). The effects on tissue fatty acid composition as well as LC-PUFA biosynthesis were addressed by first studying the quantitative endogenous production of n-3 LC-PUFA from first feeding in salmon fed marine-free diets with varying levels of linolenic:α-linoleic acid (ALA:LA) ratios. All experimental groups exhibited a significantly lower weight gain than the commercial marine control group. Endogenous n-3 LC-PUFA production was 5.9, 4.4 and 2.8 mg/g of fish when dietary ALA:LA ratios were 3:1, 1:1 and 1:3, respectively. Similarly, the decreasing dietary ALA:LA ratios also resulted in a decline in EPA:arachidonic acid (ARA) and DHA:ARA ratios.

The second study (Chapter 4), further explored the optimal period of a plant-based stimulus and the response to a similar challenge at a later period, in order to achieve an efficient programming. Results provide evidence that a one-week stimulus may be best in improving growth performance and helping salmon adapt better to a plant-based diet (V feed), although different duration periods (1 or 2 week) had little or no effect on the fatty acid composition of both total and polar lipid in several tissues. Molecular analysis revealed that the one-week stimulus upregulated several LC-PUFA biosynthetic enzymes following the challenge phase, which further supports the belief that a one-week stimulus elicits better performance and adaptation to V feed.

Further research was performed in order to investigate the long-term effect(s) of nutritional programming and challenge (Chapter 5). Applying a similar challenge to fish stimulated by a plant-based diet did not reduce salmon growth but did, however, result in a higher intracytoplasmic lipid vacuolization and lower n-3 LC-PUFA content in liver when compared to salmon fed a commercial diet. Nevertheless, the application of a stimulus elicited n-3 LC-PUFA biosynthesis in liver via the upregulation of the biosynthetic enzymes, indicating that a plant-based challenge could be considered as a booster for the early programming effects. However, further, more obvious, impacts might appear had the challenge phase been prolonged. Overall, results from the present work provide further insights into the refinement and long-term impacts of nutritional programming in order to improve the utilisation of sustainable aquafeeds for Atlantic salmon within the industry.