Globally, Chile is the second-largest producer of Atlantic salmon, a highly nutritious and widely consumed species. Domestically, salmon farming ranks as the nation’s second most important industry after copper. Concentrated primarily in the regions of Puerto Montt, Aysén, and Magallanes, this sector significantly impacts the economy, society, and science, driving employment, technological innovation, and regional development.
A persistent problem has plagued the industry in recent years: Caligus rogercresseyi, or “sea lice.” These parasites affix themselves to fish, feeding on their skin, mucus, and blood. The resulting lesions not only severely impair animal welfare but also heighten the risk of secondary infections and reduce the commercial value of the salmon.
The impact of sea lice extends beyond direct harm; it weakens Atlantic salmon, potentially making them more vulnerable to other diseases. This also forces an intensive reliance on antiparasitic drugs, whose efficacy has unfortunately waned over time. The result is a cycle of escalating production costs and a compromised future for a vital national industry.
To address this critical issue, Dr. Felipe Reyes at the University of Santiago, Chile, is spearheading the SALTsea-lice project. This research initiative focuses on how environmental factors, including water salinity and the season, influence the health and immunity of Atlantic salmon’s skin mucosa, which serves as the fish’s crucial first line of defense against sea lice.
“A key discovery was that in 16 of the past 17 years, the annual peaks of Caligus infestation consistently occur in the fall,” the researcher states. “Given that salmon are poikilothermic organisms, meaning their physiology is directly influenced by ambient temperature, this led us to a critical question: what happens during that season that renders them more susceptible?”
In light of this observation, the project employs a comparative approach, analyzing salmon cultivated in estuarine environments—where salinity is subject to fluctuations from freshwater influx—against those reared in more stable oceanic regions. The objective is to ascertain whether these environmental disparities influence the integrity of the fish’s skin mucosa and its susceptibility to parasitic infestation.
The team addresses this question by conducting their research directly within Aysén Region farming centers, ensuring they operate under real production conditions. There, they conduct a comparative analysis of fish from both estuarine and oceanic environments, meticulously examining samples including skin, mucus, scales, microbiota, blood, internal organs, and the parasite itself.
“Our goal is to integrate all available information: the fish’s reaction, the louse’s behavior, the microbiota’s role, and environmental influences,” the academic adds. “This holistic view will enable us to identify crucial patterns and develop strategies that proactively enhance fish health, moving beyond sole dependence on antiparasitic treatments.”
Complementing the study of the salmon’s immune response, the project additionally involves a detailed analysis of Caligus rogercresseyi. The team collects parasites directly from farmed fish to evaluate their development and any variations linked to the environment. This dual focus aims to reveal not only the fish’s reaction to the lice but also the lice’s adaptive strategies under varying salinity and temperature conditions.
A key innovation of this project is its season-dependent approach. The proposal aims to tailor treatments to periods when salmon are most vulnerable, acknowledging that their immune system response varies throughout the year.
“We currently treat fish as if their biology mirrors that of mammals, which is incorrect,” states Dr. Reyes-López. “Fish physiology is dictated by temperature and environmental conditions, meaning their immune system responds differently across seasons. Without accounting for this fundamental biological truth, we’re stuck applying one-size-fits-all solutions to a problem that’s inherently dynamic. Our ability to intervene more efficiently, with smarter and less invasive treatments, hinges on understanding this variability and pinpointing when and why the fish is most vulnerable.”
This Fondecyt Regular project is backed by a broad network of collaborators, including Blumar S.A. and academic teams from the University of the Americas, the University of Concepción, the University of Austral, and the University of Talca. Further strengthening SALTsea-lice are international experts Dr. Lluis Tort and Dr. Antonio Ibarz from Spain, and Dr. Brian Dixon from Canada, renowned for their leadership in fish physiology, mucous membranes, and immunity.
The Usach researcher is committed to conducting science from Chile, utilizing data from real farming conditions to tackle a global problem with contextualized solutions.
“Current technologies, largely from the Northern Hemisphere, often don’t suit our specific ecosystem or parasite,” he concludes. “Our approach is to gain a deep understanding of the fish, the pathogen, and the environment. This will enable us to achieve truly sustainable salmon farming, one that is firmly aligned with the unique production conditions of our country.”