Effect of water temperature on the morbidity of Tetracapsuloides bryosalmonae (Myxozoa) to brown trout (Salmo trutta) under laboratory conditions

Abstract

Proliferative kidney disease (PKD) is a disease found in salmonid fish that is widespread in Europe and North America. The dependency of the clinical signs on the water temperature is extensively reported in rainbow trout, but detailed information on brown trout is lacking. In this study, juvenile brown trout were exposed to the spores of Tetracapsuloides bryosalmonae and then kept at different ambient water temperatures (16°C, 19°C and 22°C) for 10 weeks along with recording of morbidity throughout the experiment. At 6, 8 and 10 weeks post-exposure, fish from each temperature group were sampled and underwent pathoanatomical examination to survey disease progression. At 16°C, brown trout showed a significantly higher survival probability compared to those kept in 19°C and 22°C water. Additionally, the parasitic burden (MSQ) was higher and the clinical signs were more pronounced in the brown trout kept at 19°C and 22°C compared with the ones kept at 16°C. This study highlights the correlation of PKD outbreaks and water temperature increases related to global climate change, which will impact the future distribution of brown trout in natural waters.

Keywords: PKD; brown trout; clinical signs; kidney swelling; survival; water temperature.

FIGURE 1

Plots of all the temperature groups showing survival probability, KSI, spleen score and mean starting quantity (MSQ) values of killed brown trout (Salmo trutta) after 10 weeks post‐exposure. Exposed groups are represented by a continuous line and control groups by dashed lines. Blue colour represents 16°C, yellow represents 19°C, and red indicates 22°C. Points denote killed fish [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 2

Box plots showing KSI, spleen score and MSQ (mean starting quantity) of sampled infected brown trout (Salmo trutta) at 6, 8 and 10 weeks post‐exposure (WPE). 16°C group in blue, 19°C group in yellow and 22°C group in red colour [Colour figure can be viewed at wileyonlinelibrary.com]