Introduction
The aquaculture industry is faced with several challenges, including access to high quality feed ingredients, and exposure to multi-stressor conditions such as changing environmental conditions and diseases leading to mortalities and economic losses. Therefore, there is an urgent need for novel, sustainable feed ingredients that can also improve the health and robustness of the fish. Microbial ingredients are viable alternatives to address the shortage of both protein and long-chain omega-3 fatty acids. Furthermore, many microbial ingredients contain bioactive components such as β-glucans, mannans and nucleic acids which can improve robustness and health of fish.
Paecilomyces variotii (PEKILO®) is a filamentous fungus that can be fermented on forestry side-streams and has promising nutritional properties for use in aquafeeds. P. variotii has a high protein content of 60-70% (dry matter basis) with a favorable amino acid composition and has shown to be rich in β-glucans and nucleotides (Hooft et al., 2024), which promote immune modulation and growth. Mensah et al. (2024) observed that spleen leukocytes exposed to P. variotii and Moritella viscosa showed up-regulation of proximal pro-inflammatory cytokines Il1β and tfnα, suggesting that P. variotii induces pro-inflammatory responses. Additionally, spleen leukocytes co-stimulated with P. variotii and M. viscosa showed immune homeostasis, with higher gene expression of il6 and tgfβ after 48 hours. These observations indicate that P.variotii can potentially boost immune responses and produce a more robust fish.
Another microbial ingredient is Schizochytrium sp., which is a microalgae specie that is high in the essential omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (Santigosa et al., 2020) and has been shown to improve mucosal barrier of skin, gills and intestine of Atlantic salmon and can replace up to 50% of fish oil (Islam et al., 2024). EPA and DHA have essential roles in many biological processes and properties like the cell membrane and cellular synthesis, and both the level and ratio of EPA and DHA have effects on the health of Atlantic salmon (Berge et al., 2019; Lutfi et al., 2023; Santigosa et al., 2023).
Methods and materials
In this experiment, vaccinated pre-smolt Atlantic salmon has been fed five different diets containing varying inclusions of P. variotii and Schizochytrium sp. in freshwater tanks for four weeks. Currently, the fish is being transferred to saltwater tanks where they will be exposed to the winter ulcer causing pathogen M. viscosa. The experiment will be concluded early June this year, and a wide range of samples will be collected.
We will present the main effects of feeding diets containing varying inclusions of P.variotii and Schizochytrium sp. for four weeks in fresh water and the effects on growth performance, robustness and health of salmon after being transferred to salt water then exposed to pathogens.
Berge, G. M., Ytteborg, E., Østbye, T.-K. K., Sundh, H., Rud, I., Sveen, L., Bæverfjord, G., Karlsen, C., Krasnov, A. & Øgaard, J. (2019). Ernæringens betydning for skinn-, tarm-, og gjellehelse hos laks. Nofima rapportserie.
Hooft, J. M., Montero, R., Morales-Lange, B., Blihovde, V. F., Purushothaman, K., Press, C. M., Mensah, D. D., Agboola, J. O., Javed, S., Mydland, L. T., et al. (2024). Paecilomyces variotii (PEKILO®) in novel feeds for Atlantic salmon: Effects on pellet quality, growth performance, gut health, and nutrient digestibility and utilization. Aquaculture, 589: 740905. doi: https://doi.org/10.1016/j.aquaculture.2024.740905.
Islam, S. M. M., Willora, F. P., Sørensen, M., Rbbani, G., Siddik, M. A. B., Zatti, K., Gupta, S., Carr, I., Santigosa, E., Brinchmann, M. F., et al. (2024). Mucosal barrier status in Atlantic salmon fed rapeseed oil and Schizochytrium oil partly or fully replacing fish oil through winter depression. Fish & Shellfish Immunology, 149: 109549. doi: https://doi.org/10.1016/j.fsi.2024.109549.
Lutfi, E., Berge, G. M., Bæverfjord, G., Sigholt, T., Bou, M., Larsson, T., Mørkøre, T., Evensen, Ø., Sissener, N. H. & Rosenlund, G. (2023). Increasing dietary levels of the n-3 long-chain PUFA, EPA and DHA, improves the growth, welfare, robustness and fillet quality of Atlantic salmon in sea cages. British Journal of Nutrition, 129 (1): 10-28.
Mensah, D. D., Morales-Lange, B., Øverland, M., Baruah, K. & Mydland, L. T. (2024). Differential expression of immune-related biomarkers in primary cultures from Atlantic salmon (Salmo salar) exposed to processed Paecilomyces variotii with or without inactivated Moritella viscosa. Fish & Shellfish Immunology, 148: 109506. doi: https://doi.org/10.1016/j.fsi.2024.109506.
Santigosa, E., Constant, D., Prudence, D., Wahli, T. & Verlhac-Trichet, V. (2020). A novel marine algal oil containing both EPA and DHA is an effective source of omega-3 fatty acids for rainbow trout (). Journal of the World Aquaculture Society, 51 (3): 649-665. doi: https://doi.org/10.1111/jwas.12699.
Santigosa, E., Olsen, R. E., Madaro, A., Søfteland, L. & Carr, I. (2023). The impact of varying EPA:DHA ratio on Atlantic salmon health and welfare. Aquaculture, 576: 739868. doi: https://doi.org/10.1016/j.aquaculture.2023.739868.