Chile holds the position as the second largest producer of the renowned Atlantic salmon (Salmo salar) globally, with a production output reaching 758,000 metric tons in 2022. Like most intensive animal food production systems, salmon farming utilizes antibiotics to manage disease outbreaks. While a downward trend in antibiotic use has been observed in recent years, 389.8 grams of antimicrobials per harvested ton were administered in Chilean salmon production last year. Notably, Piscirickettsia salmonis, a bacterium endemic to Chile, is the causative agent of a disease responsible of mortality and for over 90% of antimicrobial treatments in Chilean salmon aquaculture.
This study evaluates the association between production strategies, farming variables, and mortality due to SRS (Piscirickettsia salmonis) and antibiotic use in Atlantic salmon harvested in regions X and XI of Chile between January 2021 and June 2023. Health, production, and environmental variables were analysed at the cage level. The results indicate that production and health strategies best explain SRS mortality and antibiotic use.
Factors associated with lower SRS mortality and antibiotic use include shorter growing cycles, higher growth rates, specific genetics, use of functional diets, and a longer period before the first SRS outbreak. The analysis also revealed an association between the use of chitin inhibitors as an antiparasitic strategy and lower SRS mortality and antibiotic use.
Generalized linear mixed models (GLM) identified factors influencing SRS incidence, including time to first outbreak, mortality from sea lions and low oxygen, spring harvests, stocking in 2021 and 2022, use specific diet and breeding programs (fig 1).
Antibiotic use was associated with factors such as time to first outbreak, total mortality, temperatures above 15°C, stocking in specific years, use of oral antiparasitic treatments, and use of specific diet.
Finally, model predictions for antibiotic use were evaluated in relation to SRS mortality and three control strategies: genetics, functional diets, and vaccination. The results suggest that genetics (QTL-SRS) and specific diet are associated with lower antibiotic use.