by Vivi Koletsi, Global Technical Support, Technology Group, Alltech
Since its emergence in the late 1970s, Chile’s farmed salmon industry has evolved into a global powerhouse. By 2022, national production surpassed 1.07 million tonnes, positioning Chile as the world’s second-largest producer of farmed salmon after Norway. Beyond volume, salmon farming has become one of Chile’s most important export industries, underpinning economic growth and supporting employment and infrastructure in southern coastal regions.
Yet, this impressive growth has not come without challenges. Disease outbreaks, environmental pressures and increasing regulatory scrutiny have reshaped how producers approach health management. While early crises were dominated by viral diseases, today’s challenges are more complex, chronic and multifactorial. Among them, gill health has emerged as one of the most persistent and costly bottlenecks to sustainable salmon production.
As Chilean producers strive to balance productivity, fish welfare and environmental responsibility, gill health is increasingly viewed not as a localised pathology but as a systemic indicator of overall farm performance.
Lessons from the Past: Disease as a Catalyst for Change
Chile’s salmon industry has already experienced the consequences of underestimating health risks. Between 2007 and 2009, the outbreak of Infectious Salmon Anemia Virus (ISAV) triggered the most severe sanitary and economic crisis in the sector’s history. With an estimated direct economic impact of US$2 billion, ISAV forced widespread farm closures, job losses and significant regulatory reforms.
While viral outbreaks such as ISAV delivered acute and visible shocks, today’s gill disorders represent a more insidious threat. They develop gradually, often without obvious early signs yet can erode performance over entire production cycles. This shift from acute disease events to chronic health challenges demands a different management mindset—one that emphasizes prevention, resilience and long-term biological efficiency.
Gill Challenges in Modern Salmon Farming: A Multifactorial Problem
Gill disorders in farmed Atlantic salmon are rarely caused by a single factor. Instead, they arise from the interaction of pathogens, environmental stressors and management practices. Amoebic Gill Disease (AGD), caused by Neoparamoeba perurans, remains a major concern in high-density farming areas, including southern Chilean Patagonia. However, AGD is only part of a broader picture.
Bacteria, viruses, parasites, harmful algal blooms, elevated temperatures, reduced oxygen levels and suspended particles can all compromise gill integrity. When these factors overlap, fish may develop Complex Gill Disease (CGD)—a condition characterized by mixed lesions, inflammation, hyperplasia and impaired function. CGD is particularly prevalent during summer and early autumn, when environmental stress intensifies.
Why Gill Health Matters So Much
Gills are among the most multifunctional and delicate organs in fish. Beyond respiration and gas exchange, they play essential roles in osmoregulation, acid-base balance, detoxification, nitrogen excretion and immune defense. Structurally, gills function as a highly specialized barrier system—simultaneously microbial, chemical, physical, and immunological.
When this barrier is compromised, the consequences extend far beyond the gill itself. Affected fish often experience chronic stress, reduced feed intake, poorer feed conversion ratios, slowed growth and higher susceptibility to secondary infections. Over time, these impacts translate into increased mortality, downgraded harvest quality and reduced profitability for producers.
In short, healthy gills are foundational to healthy salmon and to sustainable aquaculture systems.
Nutritional Approaches: Building Resilience from the Inside Out
While management practices and environmental monitoring remain critical, research increasingly points to nutrition as one of the most effective levers for enhancing gill resilience. Unlike treatments applied after disease onset, nutritional strategies can strengthen barrier function proactively, helping fish cope with unavoidable stressors in their environment.
Studies across aquatic species have shown that targeted dietary interventions can improve mucosal integrity, immune responsiveness and stress tolerance—key attributes for maintaining gill health under commercial farming conditions.
MRF: A Yeast-Based Technology Supporting Gill Integrity
Alltech’s MRF (Microbial Response Factor) is a proprietary bioactive fraction derived from the yeast cell wall of Saccharomyces cerevisiae. MRF has been extensively studied in terrestrial and aquatic species for its ability to modulate immune responses and support barrier tissues.
In aquaculture, MRF has demonstrated particular relevance to gill health. Using goldfish (Carassius auratus) as a model species, research by Huang and colleagues showed that 60 days of dietary supplementation with MRF significantly increased gill lamella length and the number of mucus-producing cells. Mucus is a critical first line of defense, trapping pathogens and reducing direct epithelial exposure.
Following a 14-day pathogen challenge, fish receiving MRF exhibited:
- Higher mucus cell density
- Reduced pathogen load and infection rates
- Improved survival compared to controls
These findings highlight how nutritional support can enhance both structural and functional components of the gill barrier, before and during health challenges.
Aquate™: Tailored nutritional solutions for aquaculture
Aquate™ is Alltech’s innovative line of solutions for aquaculture production, offering a range of customisable nutritional premixes designed to maintain a protective balance between aquatic species, their nutrition and their environment. Achieving a balance between these factors helps optimise 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.
Aquate™ G: The results of a salmon cohort field trial in Chile
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. In salmon farming, gill pathologies typically develop gradually over time often leading to chronic stress, impaired growth performance and increased mortality rates if not managed effectively. Therefore, a 59-day cohort study was conducted in Chile to evaluate the effectiveness of Aquate™ G in managing gill health in farmed Atlantic salmon over time.
Field Results: Supporting Gill Health Over Time
Gill pathologies typically worsen progressively in commercial systems. However, by the end of the trial, a notable proportion of fish exhibited no visible gill lesions, reaching 37 percent and 50 percent in the two net pens.
Across both pens, the prevalence and severity of gill lesions declined over the 59-day period:
- Score 1 lesions decreased from 35 percent to 27 percent
- Score 2 lesions dropped from 46 percent to 33 percent
- Score 3 lesions declined from 14 percent to just 3 percent
Similar trends were observed in the second pen, supporting the consistency of the response under real farming conditions. These results indicate that Aquate G can help maintain and stabilize gill health over time, even in environments where chronic stressors are present.
How to Implement Nutritional Gill Support
For producers considering nutritional strategies to support gill health, several practical steps can maximize outcomes:
- Adopt a preventative mindset
Nutritional interventions are most effective when applied before severe pathology develops, particularly ahead of high-risk seasons such as summer.
- Integrate with farm management practices
Nutrition should complement—not replace—good biosecurity, environmental monitoring and stocking density management.
- Target the right life stages
Periods of transfer, thermal stress or known pathogen pressure are ideal windows for targeted nutritional support.
- Monitor outcomes consistently
Regular gill scoring and performance tracking help quantify benefits and refine feeding strategies.
What to Expect
While nutritional solutions are not a ‘silver bullet,’ producers can reasonably expect:
- Improved gill integrity and resilience
- Reduced severity and progression of gill lesions
- Better tolerance to environmental stress
- More stable growth and feed efficiency
Over time, these benefits contribute to lower biological risk and more predictable production outcomes.
Looking Ahead: Nutrition as a Pillar of Sustainable Aquaculture
As global aquaculture continues to expand, challenges like gill health will only grow in complexity. Chile’s experience highlights the importance of moving beyond reactive treatments toward integrated, science-based strategies that build resilience from within the fish.
By combining proprietary research, targeted nutritional technologies and practical farm integration, nutrition is increasingly positioned as a cornerstone of sustainable salmon production—supporting not only fish health and welfare but also the long-term viability of the industry.
