Paecilomyces variotii SUPPORTS GROWTH AND HEALTH OF ATLANTIC SALMON Salmo salar POST-SMOLT

Introduction

The Norwegian aquaculture industry is faced with several challenges, including limited access to high quality feed ingredients, and multi-stressor conditions such as changing environmental conditions and pathogen exposure leading to fish mortalities and economic losses to the industry. Consequently, there is a need for sustainable protein sources for aquafeeds with high nutritional value that also contain bioactive components with health-promoting effects. As part of the solution, microbial ingredients (MIs) such as filamentous fungi are gaining interest since they can convert low-value organic biomass into high-value nutrients, as well as they contain microbe-associated molecular patterns that can modulate the fish immune response. In addition, MIs typically have a high yield, require minimal arable land, have a low carbon footprint, and have a high potential for up-scaling to a commercial level. Thus, the use of MIs aligns with the Norwegian government's goal that all feed ingredients should come from sustainable sources, and that 25% of these should be locally sourced by 2034.

Paecilomyces variotii (PEKILO®) is a filamentous fungus that can be fermented from forestry side-streams and holds promise in novel functional aquafeeds. P. variotii has high nutritional value with a protein content of 60-70% (dry matter basis) and a favorable amino acid composition. Additionally, P. variotii is rich in β-glucans, mannoproteins and nucleotides, which have been shown to improve short-term growth performance, modulate microbiota composition and promote fish health and welfare (Hadiuzzaman et al., 2022; Hooft et al., 2024; Hossain et al., 2020; Mensah et al., 2024; Mensah et al., 2025). These observations indicate that P. variotii can be a promising sustainable protein source for aquaculture-related species, and to improve fish resilience to cope with multi-stressor conditions. Therefore, the aim of this study is to investigate the long-term effects of continuous feeding of feed containing P. variotii on growth performance, health and filet quality of post-smolts Atlantic salmon (Salmo salar).

Materials and Methods

A total of 720 vaccinated post-smolt Atlantic salmon were fed two diets in triplicates (Figure 1), containing 0% or 10% P. variotii. Prior to the start of the distribution to the net pens, the immune related tissues from 10 fish were sampled to establish a baseline. Then, fish were distributed into six net pens (5 x 5 meters, 120 fish per net pen). The fish were fed for six months, and at the end of the experiment, tissues, plasma and weight were taken from four fish per net pen and analysis of filet quality was performed of 10 fish per net pen. Preliminary results show that P. variotii supports growth performance. The experimental period ended in January 2026; fish growth performance, product quality, and multi-omics results from head kidney, spleen, and distal intestine will be presented at Aquaculture Europe 2026.

References

Hadiuzzaman, M., Moniruzzaman, M., Shahjahan, M., Bai, S. C., Min, T. & Hossain, Z. (2022). β-Glucan: Mode of Action and Its Uses in Fish Immunomodulation. Frontiers in Marine Science, Volume 9 - 2022. doi: 10.3389/fmars.2022.905986.

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.

Hossain, M. S., Koshio, S. & Kestemont, P. (2020). Recent advances of nucleotide nutrition research in aquaculture: a review. Reviews in Aquaculture, 12 (2): 1028-1053. doi: https://doi.org/10.1111/raq.12370.

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.

Mensah, D. D., Morales-Lange, B., Rocha, S. D. C., Øverland, M., Kathiresan, P., Hooft, J. M., McLean Press, C., Sørum, H. & Mydland, L. T. (2025). Paecilomyces variotii improves growth performance and modulates immunological biomarkers and gut microbiota in vaccinated Atlantic salmon pre-smolts. Fish & Shellfish Immunology, 160: 110223. doi: https://doi.org/10.1016/j.fsi.2025.110223.