A record 62.7 million salmon died in Norwegian net-pens in 2023. High mortalities in Norwegian salmon farming are caused by e.g. , pathogens, parasites, ulcers, gill diseases and intense handling operations, such as delousing procedures . As the effects of climate change become more prominent and impacts intensify , environmental conditions may increase as a risk factor to fish health.
Using downscaled temperature projections based on the Intergovernmental Panel on Climate Change (IPCC) climate projection (Shared Socioeconomic Pathways, SSPs), we have analysed potential future temperatures at selected marine fish farms in Norway. Based on the regional climate projections, we designed experimental trials with different temperature profiles reflecting the near future scenarios. Then we tested the robustness of Atlantic salmon ( Salmo salar) and Atlantic cod ( Gadus morhua ) after exposure to sub-optimal temperatures by exposing them to jellyfish fragments and reduced pH, respectively .
Results from the temperature projections show that the farming area may experience increased temperatures the next 10–15 years, including more days with temperatures above what is considered optimal for the species that are currently farmed in the areas. Sub-optimal environmental conditions induced micro-damages at the molecular and cellular levels in several organs, including gills and skin. These damages may make the fish less resilient to withstand other impacts from climate change, secondary stressors arising from climate change or general stress from the production systems. Salmon exposed to jellyfish and increased temperature in combination had more damages in gills compared to fish kept at lower temperatures, while cod had weaker scales after combined exposure to increased temperature and reduced pH.
The results can further be used to better understand how changing climate conditions in combination with secondary stressors affect fish health . Understanding how multiple stressors affect the biological performance of farmed species is essential when planning for robust production in the coming years.
The work was supported by the Norwegian Troms and Finnmark county (TFFK2021-179, SecureCod), the Norwegian Research Council (No. 194050 , Insight) , and the UK Research and Innovation Future Leaders Fellowship (MR/V021613/1).