Identification of scuticociliates (Pseudocohnilembus persalinus, P. longisetus, Uronema marinum and Miamiensis avidus) based on the cox1 sequence

Scuticociliatosis is characterized as highly histophagous, causing systemic tissue destruction and high mortality in cultured marine fish. Some of the scuticociliates have been implicated as the causative agents of scuticociliatosis. Here, we describe our study to differentially identify various species in complex animal-sourced samples, namely olive flounder Paralichthys olivaceus and black rockfish Sebastes schlegelii suffering from scuticociliatosis. The mitochondrial cytochrome c oxidase 1 (cox1) gene from the scuticociliates was amplified and sequenced. The divergence percentage of small subunit ribosomal DNA sequence between average scuticociliate species was found to be low (8.3%) but the genetic divergence of cox1 sequence reached 23.5%, suggesting that a hyper-variable region of the cox1 gene could be used as a diagnostic DNA barcoding region. Thus, we developed species-specific primers for use in multiplex PCR of complex (pooled) samples. The primers yielded species-specific fragments (of distinct size) that allowed for simple, rapid, and effective identification and differentiation of multiple species present in a single sample.

► Some of the scuticociliates are histophagous parasites.
► They cause high mortality in cultured marine fishes.
► We developed a specific multiplex PCR approach to differentially identify them.
► This method provides effective means to accomplish health monitoring in aquaculture.