Temperature-Driven Changes in Mortality and Environmental Shedding of TiLV in Nile Tilapia.

Water temperature is a critical environmental factor influencing the severity, replication and transmission of infectious diseases in aquaculture. However, its role in the pathogenesis and shedding dynamics of tilapia lake virus (TiLV), which is an emerging viral pathogen threatening global tilapia production, remains to be fully characterised. We therefore evaluated the temperature-dependent effects of TiLV infection in Nile tilapia (Oreochromis niloticus) by simulating direct and indirect cohabitation models. The fish were challenged with TiLV and maintained at 24°C, 28°C or 32°C. The highest mortality and viral loads in water and mucus occurred at 28°C, while outcomes at 32°C showed lower mortality, indicating a non-monotonic temperature response. In contrast, infection at 24°C resulted in delayed infection onset, lower viral shedding and minimal mortality among the cohabitant fish. Notably, the indirect cohabitation system consistently showed reduced transmission and lower mortality among the cohabitant fish. The TiLV concentrations in the water and mucus peaked prior to the highest mortality events in both cohabitation experiments, which supports their applicability as noninvasive early warning indicators before outbreaks occur. Our findings demonstrate that tilapia mortality and shedding dynamics of TiLV are significantly influenced by fixed water temperature. These results provide a baseline for understanding how fixed thermal regimes impact TiLV outbreaks and highlight the importance of environmental monitoring in control strategies.