DOES NUTRITIONAL PROGRAMMING INFLUENCE ATLANTIC SALMON Salmo salar RESPONSE TO MICROALGAE IN FEEDS?

Introduction

There is a need for more sustainable feed ingredients for farmed animals and Norway has a future goal that “all feed for farmed fish and livestock shall come from sustainable sources and contribute to reducing greenhouse gas emissions in the food system”. Microalgae is a promising candidate as a feed resource and in this project a marine diatom that grows fast, contains high amounts of DHA and EPA and all essential amino acids (Artamonova et al., 2017; Jónasdóttir, 2019) will be studied as a feed ingredient for Atlantic salmon (Salmo salar).

Nutritional programming is a field of research that in mammalian studies have focused on suboptimal early nutrition and predisposition of metabolic diseases later in life, while in fish there are documented effects on growth, survival and nutrient metabolism (Clarkson et al., 2017; Hou and Fuiman, 2020). Some of these documented effects of different live feeds in marine species (Imsland et al., 2006; Koedijk et al., 2010; Øie et al., 2017) could be explained by altered metabolic pathways and/or epigenetic regulation of gene expression, but there is a lack of studies addressing nutritional programming and long term effects. Previous studies in Atlantic salmon have shown that salmon can be adapted to plant-based ingredients by including these in the starter feed. The feed consumed by the salmon in its early weeks causes long-term changes in gene expression, potentially enabling the fish to better utilize new types of feed ingredients later in production (Clarkson et al., 2017; Sahlmann et al., 2015; Tawfik et al., 2024).

To evaluate the effects of early dietary exposure to diatoms on nutritional programming of Atlantic salmon fry, a 24-week freshwater feeding trial will be conducted, commencing at the onset of exogenous feeding (yolk sac absorption). The trial consists of three distinct phases also shown in Figure 1:

1. Stimulus Phase (Weeks 0–3): During the first three weeks, salmon fry will be fed one of three experimental diets containing 0%, 5%, or 10% diatom inclusion. This phase aims to initiate potential long-term changes in gene expression associated with early nutritional stimuli.
2. Intermediate Phase (Weeks 4–18): All groups will then transition to a common control diet without diatoms, allowing for assessment of the persistence of early nutritional effects without continued exposure.
3. Challenge Phase (Weeks 19–24): In the final six weeks, all groups will be challenged with a diet containing 10% diatoms to assess whether early dietary exposure influences the fish’s ability to utilize diatom-based feed ingredients later in development.

This stepwise approach represents a classical model for investigating nutritional programming.

Material and methods

Atlantic salmon fry (400-day degrees post hatch) was provided from Aquagen and transported to our facility at SINTEF in Trondheim, Norway. The trial started in 100-liter tanks with flow through fresh water at 8 °C and increased to 11 °C over 7 days with 3 experimental groups and 4 replicas resulting in 12 tanks, with 24h light. Three experimental diets with 0%, 5% and 10% microalgae were produced by Skretting, Norway. In the stimulus phase of 3 weeks, the experimental feeds were fed from the onset of exogenous feeding. In the following intermediate phase, a commercial diet (Skretting) was given and in the last 6 weeks of the trial, during the challenge phase a diet with 10% algae was provided (produced by Skretting). The pellet size of the diets was adapted to the size of the fish using advice from Skretting as a guideline. When the average weight of the fish was about 7 g the fish was pit tagged (Biomark, USA) and transferred to 2 tanks of 4,5 m3 tanks where all groups were mixed until the end of the trial. Fish was sampled after 3 weeks and before and after the challenge phase. Analysis performed was growth, microbiome in gut, gut histology, transcriptome analysis of gut and lipidomic analysis of muscle. At the end of the trial critical swimming capacity was tested in a swimming respirometer and the filet quality was tested with hyperspectral imaging.

All procedures complied with the Norwegian Animal Welfare Act of 20 December 1974, No. 73 (Sections 20–22, amended 19 June 2009). The experiment was approved by the Norwegian Food Safety Authority (FOTS ID 31092).

Results and Discussion

Results and discussion will be provided later as the trial is not finalised.

References

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Tawfik, M.M., Lorgen-Ritchie, M., Król, E., McMillan, S., Norambuena, F., Bolnick, D.I., Douglas, A., Tocher, D.R., Betancor, M.B., Martin, S.A.M., 2024. Modulation of gut microbiota composition and predicted metabolic capacity after nutritional programming with a plant-rich diet in Atlantic salmon (Salmo salar): Insights across developmental stages. https://doi.org/10.21203/rs.3.rs-3857255/v1