Enhancing quality and reducing melanin spots with QRILL Aqua

Atlantic salmon is one of the world’s most popular seafoods, renowned for its nutritional benefits that support human health. The salmon farming industry significantly contributes to the economies of the producing countries, providing employment and supporting related sectors such as feed production, processing, and equipment manufacturing.

Flesh quality: A key success factor

High performance during production, as well as resilience against diseases and stress, are important success factors in Atlantic salmon farming. Good health and welfare are keys to both profitable and responsible farming, and is also the critical factors that influence the flesh quality of the final product. The quality and appearance of the fillet is important as it influences consumer purchasing decisions. Processing plants classify quality based on several characteristics, including pigmentation, texture, and uniformity. One major issue that reduce the share of premium product is the presence of dark spots known as melanin spots or melanosis in the fillet.

Melanin is a naturally occurring pigment in salmon, forming dark spots on the skin, and also occurs in the immune system as part of the fish’s immune defense against pathogens. The quality issues arise when these dark pigments accumulate in the fillet, appearing as spots or a diffuse discoloration through the whole fillet. This necessitates the removal during processing, leading to increased labor costs and reduced product yield. Diffuse discoloration can result in downgrading or, in the worst case the discarding of the entire fillet, causing significant economic losses.

Issues with melanin accumulation affect operations in several major salmon producing countries. In Norway, the reports indicate that as much as 20% of the harvested salmon is impacted, and in Chile almost 30% of downgraded fillets is downgraded due to melanosis, according to Aquabench. Melanin spots have a significant impact on the salmon industry as a whole, and any tool that can reduce the occurrence of these spots will be of great importance to the industry. To understand the available solutions, and why krill meal might be part of the answer, it is essential to understand the mechanisms behind the formation of these dark spots and the underlying causes of their development.

The link to inflammation

Melanin pigments in the flesh of salmon are linked to inflammation in the fillet. While the exact cause of the problem is unclear, the process typically begins with a bleed or trauma in the flesh, triggering melanin-producing cells – melanomacrophages, as a part of the immune response to fight or seal off the pathogens and clean up the damage caused by the trauma. Recent science has also linked the initiation to hypoxia and necrosis of fat cells that triggers the inflammation cascade in the fillet. If the inflammatory response is optimal, the immune system cleans up the damage, and the fillet returns to a healthy state. However, if the inflammatory process becomes chronic and the fish does not return to a healthy state, the pigments continue to accumulate in the fillet, thus compromising the fillet quality.

Chronic inflammation in animals, including salmon, has been linked to long term exposure to stress. Stressors in intensive farming environments include diseases, rough weather, and handling procedures. One way to combat chronic inflammation is by ensuring sufficient omega-3 intake, specifically EPA and DHA fatty acids. These fatty acids are part of the anti-inflammatory pathways in the immune system and may reduce the chance of an inflammatory process becoming chronic and harmful. Research has shown that low levels of EPA and DHA in fish feed is associated with less robust fish that are prone to chronic stress. Access to antioxidants will also influence the oxidative state in the musculature, and may also impact the development of dark spots in the fillet.

Several researchers have investigated the impact of increased EPA and DHA levels on melanin occurrence in the fillet. In a comprehensive report (EX-spot 2022), the authors concluded that higher EPA and DHA levels clearly reduced the severity of the melanosis. They also found that DHA, in particular, seems to inhibit tyrosinase, an enzyme that is involved in the production of melanin pigments in the cells.

QRILL Aqua may reduce the severity of melanin spots

QRILL Aqua, a meal made from Antarctic krill, is a rich source of EPA and DHA in a highly effective phospholipid form. This form ensures the uptake of the fatty acids in the digestive system and their deposition in cells membranes in the tissues, where they help balance the inflammatory process.

In an internal trial by Aker BioMarine researchers found that higher EPA and DHA levels from krill meal in the feed had great impact on melanosis in the fillet. The trial showed that the addition of 7,5% of QRILL Aqua in a diet fed to Atlantic salmon from 1.2 kg to 3.2 kg completely eliminated the occurrence of dark spots in the fillet. These results align with previous studies with krill meal.

The benefits of krill meal and the reasons behind its ability to reduce dark spots go beyond its high levels of EPA and DHA in phospholipid form. Krill meal also provides selenium and zinc in organic form, key minerals linked to melanosis reduction. Additionally, krill meal contains natural antioxidants like astaxanthin, vitamin E, and vitamin C, which are beneficial for reducing melanin spots.

Including krill meal in the feed not only enhances palatability and increases feed intake and growth, it also supports the overall robustness of salmon and improves the final product quality. For salmon farmers, key drivers of cost-effectiveness are growth, health, and premium product quality. Adding QRILL Aqua to salmon diets can significantly contribute to these success factors and lead to better results, and thus play a role in the success of the farmer.

 References:

• Aquabench Melanosis Project. (2022, September 5). Melanosis Project Description. https://aquabench.com/en/2022/09/05/melanosis-project/
• Mørkøre, T., Larsson, T., Jiménez-Guerrero, R., Moreno, H. M., Borderias, J., Ruyter, B. S., … & Bæverfjord, G. (2022). EX-spot: Mørke flekker i laksefilet. Årsak til dannelse og tiltak som hemmer utvikling. Nofima Rapportserie.
• Bjørgen, et al. (2024). Deciphering the pathogenesis of melanized focal changes in the white skeletal muscle of farmed Atlantic salmon (Salmo salar).
• Lutfi, et al. (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.
• Färber, J. (2017). Melanin spots in Atlantic salmon fillets – An investigation of the general problem, the frequency and the economic implication based on an online survey.
• Bjørgen, et al. (2015). Piscine orthoreovirus (PRV) in red and melanised foci in white muscle of Atlantic salmon (Salmo salar). Veterinary Research, 46(1), 1-12.

Wakamatsu, K. (2023). Eumelanin Detection in Melanized Focal Changes but Not in Red Focal Changes on Atlantic Salmon (Salmo salar) Fillets. International Journal of Molecular Sciences, 24, 16797. https://doi.org/10.3390/ijms242316797