In recent years, many firms in Chile’s salmon aquaculture industry have committed to reducing their use of antibiotics. While national data suggests substantial progress, achieving these targets is likely to be both challenging and expensive as there exist few alternatives to antibiotics for treating common infections, such as Piscirickettsiosis. In this paper, we explore how the design of antibiotic-use restrictions is likely to impact the productivity of fish farms exposed to a communicable disease. Leveraging insights from both economics and epidemiology, we develop a stylized model of a farm as a forward-looking, profit-maximizing entity where the biomass at harvest is determined by a compartmental model of disease dynamics. Farm managers control disease by applying treatment with temporary effectiveness. Further, we assume that pathogens are transmissible between individuals on the farm and between farms in a region, such that the disease management choices of one farm impact its neighbors. We solve the model as a finite-horizon, deterministic optimal control problem and simulate a selection of restrictions that are parameterized to achieve a targeted reduction level.
Our model suggests that the optimal treatment strategy is a function of both on-farm disease dynamics and ambient disease levels. However, in many scenarios, a reduction in ambient disease pressure does little to reduce optimal antibiotic-use. We also illustrate that, consistent with a theory, a cap on the total quantity of antibiotics used in a production cycle is the most cost-effective policy for achieving an intended target, when compared to more restrictive policies.