Effects of Different Preservatives During Ecological Monitoring of Myxozoan Parasite <i>Tetracapsuloides bryosalmonae</i> Causing Proliferative Kidney Disease (<scp>PKD</scp>) in Salmonids

Effective sample preservation is essential in large-scale population monitoring, particularly for molecular genetic analyses of pathogens, and for measuring disease symptoms in hosts. In such monitoring cases, disease symptoms can indicate poor habitat health, as they often coincide with elevated temperatures and suboptimal environmental conditions. This study examines the effect of two preservatives; 95% ethanol and 99% isopropanol on the assessment of proliferative kidney disease (PKD) in the renal tissue of young-of-the-year brown trout (Salmo trutta). Specifically, we studied the effect of preservatives on the physical measurement of a primary symptom of PKD, renal hyperplasia. Furthermore, we evaluated the effect of preservatives on the molecular detection and quantification of the causative PKD agent myxozoan parasite Tetracapsuloides bryosalmonae. Our results indicate that isopropanol-preserved samples exhibit greater renal tissue shrinkage, with the most pronounced differences observed in smaller fish when compared to ethanol-preserved samples. This difference in shrinkage is great enough to disguise symptomatic fish when observing renal hyperplasia with mixed storage mediums. However, both preservatives were found to be suitable for DNA extraction of sufficient quality for detection and quantification of the parasite using qPCR with no statistically significant differences in DNA yield or parasite load due to the type of preservative. We found that while ethanol is preferable for ease of dissection, isopropanol is a suitable alternative for PKD monitoring in wild fish, especially where access to ethanol may be limited. Understanding the difference in tissue shrinkage caused by the two preservatives can enable compensatory adjustment and maintain higher standards of data accuracy when assessing the severity of Tetracapsuloides bryosalmonae infection.