Identification of the pathogenic ciliate Pseudocohnilembus persalinus (Oligohymenophorea: Scuticociliatia) by fluorescence in situ hybridization

Many scuticociliatid ciliates are regarded as devastating pathogens in aquaculture. Among these, Pseudocohnilembus persalinus is a facultative pathogen that often results in refractory diseases of mariculture fish. Although traditional silver staining methods have been successfully used to identify these ciliates, their identification is hampered by their small size and their morphological similarity to closely related species. We designed an alternative method of identification of P. persalinus using an SSU-rDNA targeted oligonucleotide probe labeled with a fluorochrome, and optimized in a fluorescence in situ hybridization (FISH) protocol. The assay results in a clear identification by strong fluorescence signals from the oligonucleotide probe. The method can be used for quick and early detection of P. persalinus infections on host fish, as well as other susceptible organisms in aquiculture water. It may also be used in studies of the geographical distribution of this scuticociliate.