Data from: Parasite infection and decreased thermal tolerance: impact of proliferative kidney disease (PKD) on a wild salmonid fish in the context of climate change

Parasites and pathogens can have an important effect on their host's
thermal resistance. The impact of parasite infection on host physiological
performances has traditionally been studied in controlled laboratory
conditions, and much less is known about its actual effects in wild
populations. Nonetheless, such knowledge is critical when assessing the
effect of climate change on the future survival of the host.
Tetracapsuloides bryosalmonae is a myxozoan endoparasite causing
proliferative kidney disease (PKD) in salmonids. Infection and clinical
symptoms of PKD are dependent on environmental temperature and PKD has
become an emerging disease of primary importance for farmed and wild
salmonids in the last decades. Despite important achievements in
understanding PKD pathology in recent years, there are still crucial gaps
in the knowledge of the disease ecology, notably in how the parasite
affects host performance in the wild. We sampled juvenile (0+) brown trout
(Salmo trutta) from the wild during early and late summer and assessed
relative parasite load (DNA quantification with qPCR) and disease severity
(kidney hyperplasia). We also measured haematocrit, leucocyte formula,
aerobic scope and upper thermal tolerance in a field-physiology approach
in order to better understand the relationships between PKD severity and
host performance. By using wild-caught individuals and performing
measurements directly on location, we aimed to gain insights into host
physiology in a natural environment while avoiding biases caused by
laboratory acclimation. We found that most physiopathological symptoms in
the wild were strongly correlated with kidney hyperplasia, but more weakly
linked to parasite load. Disease severity was positively correlated with
anaemia and abundance of circulating thrombocytes, and negatively
correlated with aerobic scope and thermal tolerance. Our results suggest
that impaired aerobic performances and thermal tolerance in infected fish
may potentially result in decreased host survival in the wild, especially
in relation with predicted higher average summer temperatures and
increased frequency of extreme events (summer heatwaves) in the context of
global climate change.