Gill health in salmon: Chile’s nutritional approach

Salmon from Chile

Since its development in the late 1970s, Chile's farmed salmon industry has grown substantially, surpassing 1.07 million tons of production in 2022 (FAO, 2024). Today, Chilean salmon ranks as the second-biggest source of farmed salmon in the world after Norwegian salmon, and the sector has become one of the country’s largest export industries, playing a vital role in the national economy and the development of local communities (Ceballos‐Concha et al., 2025).

Disease challenges in Chilean salmon farming

This growth, however, has not been linear; the Chilean farmed salmon industry has faced disease outbreaks that have triggered severe economic and sanitary crises, as well as subsequent policy reforms (Bachmann-Vargas et al., 2021). Between 2007 and 2009, the rapid spread of the infectious salmon anemia virus (ISAV) caused the most significant disease outbreak and economic crisis in the history of Chilean salmon farming, with an estimated direct economic impact of US$2 billion (Mardones et al., 2024).

While viral outbreaks like ISAV have had the most devastating impact, gill disorders have emerged more recently as a persistent and increasingly complex health challenge for salmon aquaculture production (Fridman et al., 2021).

Emerging gill health challenges

Amoebic gill disease (AGD), which is caused by the parasite Neoparamoeba perurans, continues to be a major concern — particularly in large-scale farming areas with high stocking densities, such as the Patagonian region of southern Chile (Bustos et al., 2011). The combined effects of multiple pathogens, including bacteria, viruses and parasites; environmental stressors, such as rising water temperatures and declining water quality; and certain management practices can increase the risk and severity of gill disorders (Rozas et al., 2012). These factors may contribute to the development of complex gill disease (CGD), a condition characterized by a multifactorial etiology and complex histopathological patterns (Herrero et al., 2018), particularly during the summer and early autumn months.

Why are healthy gills critical for successful salmon farming?

Salmon gills are multifunctional organs that are responsible not only for respiration and gas exchange but also for ion regulation (osmoregulation), the pH balance, detoxification, the excretion of nitrogenous waste and immune defenses (Evans et al., 2005). Healthy gills function as a complex barrier system that serves as a microbial, chemical, physical and immune barrier, playing a key role in the host’s defenses against pathogens (Chen et al., 2023). Disruption of the gill barrier in Atlantic farmed salmon can impair gill functions, leading to chronic stress, reduced growth, poor feed conversion and increased mortality — all of which are factors that ultimately threaten the production of high-quality salmon and the profitability of salmon farmers (Herrero et al., 2018).

Nutritional strategies for enhancing gill health

Research indicates that improving gill barrier functions in farmed salmon — and fish in general — can help them cope with stress brought on by uncontrolled environmental factors. Several studies have shown that the most effective way to achieve this enhancement is through appropriate interventions in the diet composition (Chen et al., 2023). A mannan-rich fraction (MRF) from Alltech, derived from the yeast cell wall of Saccharomyces cerevisiae, has been studied in aquatic species for its role in protecting gill surfaces both prior to and during pathogen challenges.

Using goldfish (Carassius auratus Linnaeus) as a model species, Huang et al. (2022) demonstrated that dietary supplementation with MRF over 60 days significantly increased the gill lamella length and the number of mucus cells in the gills (Figure 1). Following a 14-day pathogen challenge, the goldfish fed the MRF-enriched diet exhibited a greater number of mucus cells, as well as reduced pathogen loads and infection rates and higher survival rates (Figure 2), than the control group.

Figure 1. After 60 days of feeding, the gills of goldfish in the MRF group exhibited longer lamellae and a higher number of mucus cells compared to the control group (Huang et al., 2022).

Figure 2. After 14 days of pathogen challenge, goldfish in the MRF group exhibited a higher number of mucus cells in the gills, lower pathogen counts and infection rates, and a higher survival rate compared to the control group (Huang et al., 2022).

Aquate™: Tailored nutritional solutions for aquaculture

Aquate™ is Alltech’s innovative line of solutions for aquaculture production, offering a range of customizable nutritional premixes designed to maintain a protective balance between aquatic species, their nutrition and their environment. Achieving a balance between these factors helps optimize animal performance and maintain healthy fish populations.

Developed through close collaborations with aqua producers globally, Aquate™ solutions incorporate Alltech’s core technologies — including peptide technologies, solid-state fermentation and yeast fermentation. These blends are tailored to specific production goals based on the species, life stage and environmental or health-related challenges. Aquate™ solutions help producers unlock their animals' true potential and enhance their own profitability.

In response to the heightened gill health challenges in Chilean salmon farming, Alltech has introduced a targeted nutritional solution as part of the Aquate™ family of offerings. To learn more, read about a gill health trial studying this new solution with farmed Atlantic salmon in Chile or contact the Alltech Chile team for details on our customized Aquate™ solutions.

References

Bachmann-Vargas, P., van Koppen, C. K., & Lamers, M. (2021). Re-framing salmon aquaculture in the aftermath of the ISAV crisis in Chile. Marine Policy, 124, 104358.

Bustos, P. A., Young, N. D., Rozas, M. A., Bohle, H. M., Ildefonso, R. S., Morrison, R. N., & Nowak, B. F. (2011). Amoebic gill disease (AGD) in Atlantic salmon (Salmo salar) farmed in Chile. Aquaculture, 310(3-4), 281-288.

Ceballos‐Concha, A., Asche, F., & Cárdenas‐Retamal, R. (2025). Salmon Aquaculture in Chile: Production Growth and Socioeconomic Impacts. Reviews in Aquaculture, 17(1), e12993.

Chen, X., Liu, S., Ding, Q., Teame, T., Yang, Y., Ran, C., ... & Zhou, Z. (2023). Research advances in the structure, function, and regulation of the gill barrier in teleost fish. Water Biology and Security, 2(2), 100139.

Evans, D. H., Piermarini, P. M., & Choe, K. P. (2005). The multifunctional fish gill: dominant site of gas exchange, osmoregulation, acid-base regulation, and excretion of nitrogenous waste. Physiological reviews, 85(1), 97-177.

Fridman, S., Tsairidou, S., Jayasuriya, N., Sobolewska, H., Hamilton, A., Lobos, C., ... & Herath, T. (2021). Assessment of marine gill disease in farmed Atlantic salmon (Salmo salar) in Chile using a novel total gross gill scoring system: A case study. Microorganisms, 9(12), 2605.

Herrero, A., Thompson, K. D., Ashby, A., Rodger, H. D., & Dagleish, M. P. (2018). Complex gill disease: an emerging syndrome in farmed Atlantic salmon (Salmo salar L.). Journal of Comparative Pathology, 163, 23-28.

Huang, X., Liu, S., Zuo, F., Luo, L., Chen, D., Ou, Y., ... & He, Z. (2022). cMOS enhanced the mucosal immune function of skin and gill of goldfish (Carassius auratus Linnaeus) to improve the resistance to Ichthyophthirius multifiliis infection. Fish & Shellfish Immunology, 126, 1-11.

Mardones, F. O., Martinez-Lopez, B., Valdes-Donoso, P., Carpenter, T. E., & Perez, A. M. (2014). The role of fish movements and the spread of infectious salmon anemia virus (ISAV) in Chile, 2007–2009. Preventive veterinary medicine, 114(1), 37-46.

Rozas, M., Bohle, H., Grothusen, H., & Bustos, P. (2012). Epidemiology of amoebic gill disease (AGD) in Chilean salmon industry between 2007 and 2010. Bulletin of the European Association of Fish Pathologists, 32(5), 181-188.

About the author:

Dr. Vivi Koletsi is a global technical support specialist within Alltech’s Technology Group. She collaborates with the company’s global Aqua team regarding all technologies on the aquatic species side.   

Dr. Koletsi, a native of Ioannina, Greece, first became interested in aquaculture while completing her undergraduate studies in biology at the Aristotle University of Thessaloniki. She began focusing on fish nutrition in earnest while pursuing her master’s degree in aquaculture and marine resource management at Wageningen University & Research in the Netherlands. This interest led her to complete an internship with Alltech Coppens, during which she established a protocol to help prevent mycotoxin contamination in aqua feeds. 

Upon earning her master’s degree, Dr. Koletsi continued her mycotoxin research at the doctoral level with support from Alltech in collaboration with the Aquaculture and Fisheries Group at Wageningen University & Research. While completing her doctoral studies, Dr. Koletsi conducted trials at Alltech Coppens’ facilities while continuing laboratory work at Wageningen. Her focus was on mycotoxins’ impact on rainbow trout.  

Dr. Koletsi joined Alltech as a team member upon completion of her Ph.D. in 2023. 

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