Use of antimicrobials in Chilean Salmon farming: Facts, myths and perspectives

Chile is the second largest producer of salmon (only behind Norway), and high amounts of antimicrobials are used during the marine stage, mainly florfenicol. Intensive antimicrobials use is a relevant concern, prompting the urgent need for use reduction and advancements towards more restricted, efficient application. This review describes the historic and current use of antimicrobials in Chilean salmonid farming. Further covered is the experimental evidence reported to date, thus providing a clearer understanding for the pathogenic nature of Piscirickettsia salmonis-the most important bacterial pathogen and the main target of antimicrobials used in the Chilean industry. This review also assesses research exploring the impacts of antimicrobial treatment on the environment, as well as investigations on the antibiotic susceptibility of salmonid pathogens. This review of the scientific literature contributes to a more unbiased appraisal of the current situation in Chile. Unfortunately, various previous reports dealing with/on the antimicrobial use in the Chilean salmon farming industry have been arrived to insufficiently supported conclusions, thus the present review aims to clarify outdated or poorly substantiated information and assumptions in existing literature. The consequences of antimicrobials in fish farming are covered by this review, which is particularly relevant considering potential impacts on aquatic environments. Focus is given to the selection and spread of drug-resistant bacteria and associated resistance-encoding genes. Finally, herein are provided several recommendations from a One Health perspective for decreasing amounts of used antimicrobials, effectively controlling primary bacterial fish pathogens, developing proper prevention strategies and reducing the dissemination of antimicrobial resistance.