The Chilean Fisheries Development Institute (IFOP) held a virtual workshop to disseminate the results of its program Determination and Monitoring of Caligus rogercresseyi Resistance to Antiparasitics Applied in National Salmon Farming. Stage VIII (2024–2025). This initiative aims to strengthen technical knowledge and support sanitary decision-making within the salmon farming industry.
The event, organized by IFOP's Department of Hydrobiological Health, brought together representatives from the public sector, the industry, and the scientific community. Its goal was to share the main advancements of the program, which has been running continuously for eight years.
Jaiber Solano Iguarán, senior researcher at IFOP, highlighted that, to date, 254 valid bioassays have been conducted in 95 samplings, covering 28 Salmon Farming Concession Areas (ACS) in the Los Lagos and Aysén regions. During this period, the parasite's susceptibility has been evaluated primarily against azamethiphos, deltamethrin, and cypermethrin.
The results show variations in susceptibility profiles between compounds and geographical zones. For azamethiphos, an increasing trend was observed in the EC50 value (median effective concentration, i.e., the dose affecting 50% of exposed parasites), reinforcing the importance of diversifying available control tools and monitoring their efficacy over time. In contrast, EC50 values for deltamethrin and cypermethrin showed a decreasing trend, which could indicate a better parasite response to these compounds in some areas.
Additionally, methodological advancements of the program were highlighted, such as the analysis of parasite morphometry and its association with environmental and treatment variables, as well as the initiation of bioassay validation for non-pharmacological compounds. This stage included evaluations with hydrogen peroxide and plant extracts, opening new avenues of work for products currently in use in the industry.
The collaborative effort among the Undersecretariat of Fisheries and Aquaculture (Subpesca), the National Fisheries and Aquaculture Service (Sernapesca), and IFOP has been crucial in the development of this program. It will continue with new activities during the second half of 2025. According to Solano, future challenges include studying the genetic connectivity among Caligus populations, expanding the program's geographical coverage, and strengthening the temporal analysis of susceptibility profiles.
