New data on flatfish scuticociliatosis reveal thatMiamiensis avidusandPhilasterides dicentrarchiare different species

Abstract

SUMMARYScuticociliatosis is a severe disease in farmed flatfish. However, the causative agent is not always accurately identified. In this study, we identified two isolates of scuticociliates from an outbreak in cultured fine flounderParalichthys adspersus. Scuticociliate identification was based on morphological data, examination of life stages and the use of molecular approaches. The isolates were compared with a strain ofPhilasterides dicentrachifrom turbotScophthalmus maximusand with a strain deposited in the American Type Culture Collection asMiamiensis avidusATCC®50180™. The use of morphological, biological and molecular methods enabled us to identify the isolates from the fine flouder asP. dicentrarchi. Comparison ofP. dicentrachiisolates andM. avidusrevealed some differences in the buccal apparatus. UnlikeP. dicentrarchi, M. avidushas a life cycle with three forms: macrostomes (capable of feeding onP. dicentrarchi), microstomes and tomites. Additionally, we found differences in the 18S rRNA and α- and β-tubulin gene sequences, indicating thatP. dicentrarchiandM. avidusare different species. We therefore reject the synonymy/conspecificity of the two taxa previously suggested. Finally, we suggest that a combination of morphological, biological, molecular (by multigene analysis) and serological techniques could improve the identification of scuticociliates parasites in fish.