Bryozoans as hosts for Tetracapsula bryosalmonae, the PKX organism

Abstract

Freshwater bryozoans have recently been identified as hosts of Tetracapsula bryosalmonae, the causative agent of proliferative kidney disease (PKD). To gain insight as to which bryozoans are consistently important hosts for T. bryosalmonae, we present the results of a broad scale survey of bryozoans in European and North American sites upstream from PKD outbreaks in feral, stocked and farmed salmonids. The bryozoan genera most commonly found in association with disease outbreaks are Fredericella and Plumatella, and the most common species are F. sultana (Blumenbach), F. indica Annandale, and P. emarginata Allman. The prevalence of mature sac stages of T. bryosalmonae was very low. Our survey data together with knowledge of bryozoan life cycles and the ecology of PKD allow inferences concerning unknown aspects of the life cycle of T. bryosalmonae.