Abstract
The 5.8S rRNA gene of C. irritans in water and mud substrate samples were quantified at 6 or 7 stations in Nomi Bay, Kochi, Japan twice a month from the late June to the middle December, using a TaqMan real-time PCR assay developed in the present study. The number of copies of the gene in water peaked at 4:00 am over a 20-h sampling period in October. The mean numbers of the gene copies equivalent to 4.465-6,590 theronts/L were detected from water sampled at a station close to cages containing great amberjack Seriola dumerili affected with cryptocaryoniasis in early October and late November, when cryptocaryoniasis outbroke. The frequency of detection of the gene in the substrate mud was highest at a station far from the affected area, suggesting that the distribution of tomonts of C. irritans were influenced with tidal currents. The 18S-ITS1 region of C. irritans was PCR-amplified from a water sample, sequenced and compared with the sequences previously obtained from the parasite of various localities. The present sequence was contained in a clade mainly comprising the sequences obtained in China, suggesting that the greater amberjack juveniles imported from southern China was a source of C. irritans in Nomi Bay.
