Impact of Surveillance and Depopulation Strategies on Fish Disease Transmission Among Net‐Cage Farms Near the Tongyeong Coast Based on a Spatiotemporal Hybrid Approach

Infectious diseases among fish farms present significant challenges to fish health and production. Horizontal transmission serves as one of the main mechanisms driving outbreaks in these settings. The dynamics of horizontal transmission are influenced by pathogen properties, host characteristics and environmental factors. Additionally, the implementation of epidemiological interventions can further shape the patterns and consequences of infectious disease spread. However, there is a paucity of studies assessing how specific epidemiological measures, such as timely disease surveillance and strategic depopulation, influence transmission and outbreak outcomes. This study utilized a spatiotemporal hybrid model to assess pathogen dissemination following an infectious disease event in Tongyeong, a prominent area for floating net cage aquaculture in Korea. We investigated how variations in sampling intensity affected the timing of disease detection and analysed the impact of two control strategies (immediate culling upon detection versus no culling) on the progression of disease and fish mortality. Findings revealed significant differences in disease detection timing and probability based on the surveillance sampling size. Early detection of disease was achieved when 100 fish were sampled, as opposed to a delayed response when only 5 fish were tested. Furthermore, the conditions under which surveillance occurred had a notable impact on both the spatial spread and the success of depopulation measures. Generally, prompt detection followed by immediate depopulation led to a decrease in disease-related mortality over a wider area. However, this method also necessitated culling a substantially greater number of fish. Although the impact of these interventions may be influenced by geographical and environmental variables, our results suggest that the utility of depopulation strategies is closely linked to the efficacy of surveillance efforts and the epidemiological profile of the infection, such as its associated mortality rate and transmissibility.