Antibiotic use in Chile: 'The next step is to reduce the transmission of SRS'

The Chilean salmon sector can no longer continue to reduce antibiotic use without an increased focus on reducing the transmission of disease, an epidemiologist and former fish vet has said.

The assessment by Dr Fernando Mardones, a senior lecturer at the University of Edinburgh, follows the latest report on antibiotic use in the salmon farming industry prepared by state aquaculture agency Sernapesca.

Chile’s salmon farmers have achieved a relatively steady decline in antibiotic use since 2015, when the annual Antimicrobial Consumption (AMC) – measured as a percentage of active ingredients per tonne of fish produced – reached 0.063%.

That percentage gradually decreased until 2023, when it stood at 0.031%, however 2025 ended with an increase to 0.034% AMC.

A limit of efficient control

Mardones told Fish Farming Expert’s Chilean sister site, Salmonexpert.cl, that this reflects the fact that the Chilean salmon farming industry has reached a “limit of efficient control” under the current approach, and that from an epidemiological perspective, this pattern is not unexpected.

From around 2018 increased investment in research and development, including public initiatives such as the Strategic Investment Fund (FIE), focused on key diseases like salmon rickettsial septicaemia (SRS) and the control of the Chilean sea louse, Caligus rogercresseyi.

These investments contributed to a greater scientific understanding of the biology of these diseases and their dynamics in production systems, and ended the historically linear relationship between biomass production and antibiotic use: that is, greater production no longer necessarily corresponds to greater antibiotic use.

However, in recent years the ICA has stabilised, suggesting that the system has reached a limit in its current capacity to reduce antibiotic use. This scenario reflects a predominant focus on early detection and timely treatment of the disease. This approach has been effective in decreasing the prevalence of SRS, as well as mitigating its impact on production and animal welfare. However, it is primarily a reactive strategy, which does not necessarily reduce the occurrence of new cases.

The next step

“Today the industry has made progress in treating the disease better, but the challenge is to prevent it better. In other words, the industry has already optimised treatment; the next step is to reduce transmission,” says Mardones.

From an epidemiological perspective, this shift implies moving from a prevalence-focused approach to one aimed at reducing incidence. This requires strengthening evidence-based prevention strategies, both at the farm level and within production groups (e.g.: agricultural control associations).

To this end, Mardones advocates prioritising preventative measures such as net cleaning, optimising production cycles and stocking synchronisation, timely removal of diseased fish, and aspects related to improving smolt quality and robustness.

Costs and benefits

These measures involve additional costs, so one of the main challenges for the industry is having tools that allow for quantifying their health and economic impact, facilitating better decision-making. To move forward in this new stage, the next step falls primarily on the industry, through increased investment in applied studies under real production conditions, says Mardones. The goal is to generate robust evidence that allows for evaluating the impact of preventative measures in the field.

“The industry needs to quantify both the cost and the health benefits of these interventions in order to prioritise those that are most effective and cost-efficient. This is key to moving towards a more efficient disease control system with less dependence on antibiotics,” he explains.