Spatial and intra-host distribution of myxozoan parasite Tetracapsuloides bryosalmonae among Baltic sea trout (Salmo trutta)

Proliferative kidney disease caused by the myxozoan parasite Tetracapsuloides bryosalmonae has been actively studied in juvenile salmonids for decades. However, very little is known about parasite prevalence and its geographical and intra-host distribution at older life stages. We screened T. bryosalmonae among adult sea trout (Salmo trutta) (n = 295) collected along the Estonian Baltic Sea coastline together with juvenile trout from 33 coastal rivers (n = 1752) to assess spatial infection patterns of the adult and juvenile fish. The parasite was detected among 38.6% of adult sea trout with the prevalence increasing from west to east, and south to north, along the coastline. A similar pattern was observed in juvenile trout. Infected sea trout were also older than uninfected fish and the parasite was detected in sea trout up to the age of 6 years. Analysis of intra-host distribution of the parasite and strontium to calcium ratios from the otoliths revealed that (re)infection through freshwater migration may occur among adult sea trout. The results of this study indicate that T. bryosalmonae can persist in a brackish water environment for several years and that returning sea trout spawners most likely contribute to the parasite life cycle by transmitting infective spores.

Automated summary

Proliferative kidney disease caused by Tetracapsuloides bryosalmonae has been extensively studied in juvenile salmonids, but little is known about parasite prevalence and distribution in adult fish. This study examined adult sea trout and juvenile trout along the Estonian Baltic Sea coastline and found that the parasite was present in 38.6% of adult sea trout, with higher prevalence in the eastern and northern regions. Similar infection patterns were observed in juvenile trout. The study also revealed that the parasite can persist in brackish water for several years and that freshwater migration may contribute to reinfection in adult sea trout.