Large-scale spatial analyses reveal thermal onset and disease hotspots of proliferative kidney disease in brown trout
Year: 2025
Type: preprint
Abstract: Proliferative kidney disease (PKD) poses a threat to wild salmonids, yet its spatial patterns remain poorly understood, particularly at large scales. We combined a first nationwide screening of brown trout (Salmo trutta) consisting of 1072 fish from 160 locations with process-based stream-temperature modelling, which increases the accuracy of predicted temperatures, to map infection by the parasite Tetracapsuloides bryosalmonae, quantify parasite load (using qPCR from kidney tissue), and calculate renal hyperplasia across Sweden. PKD occurred once study-period mean water temperatures approached a threshold of approximately 15.4 °C and renal hyperplasia peaked near 17 °C, however warm water did not always cause disease: asymptomatic infections were common above the temperature threshold. Broadly, hotspots for severe pathology clustered in southern Sweden, whilst cold spots occurred in the north and mountainous regions. However, dams and shallow lakes sometimes caused deviations from such biogeographic patterns, whereby the northernmost PKD case and T. bryosalmonae infection occurred downstream of dams. Furthermore, we identified a mid-Sweden coastal hotspot that would be missed by assuming a simple latitudinal trend for disease traits. Variation was present at fine scales where bryozoan abundances and additional environmental drivers may be affecting the epidemiology. Management actions that re-establish riparian shade or remove small impoundments can reduce thermal exposure and infection pressure.
Authors: Duncan Philpott, Joacim Näslund, Serena Donadi, Anti Vasemägi
Institution: Swedish University of Agricultural Sciences
Language: English
Subfield: Cancer Research
Domain: Life Sciences
Open Access status: gold
OpenAlex ID: W4415031137
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