Molecular diagnostics for verifying an etiological agent of emaciation disease in cultured olive flounder Paralichthys olivaceus in Korea

Enteromyxum leei and Parvicapsula anisocaudata have been reported to cause emaciation disease in cultured olive flounder Paralichthys olivaceus in Jeju Island, Korea, but there is no consensus regarding its causative agent. A total of 60 cultured olive flounders were obtained from 12 fisheries, and divided into 5 groups according to their relative condition factor. We investigated the correlation between the relative condition factor and parasite infection using molecular diagnostics to identify the etiological agent of the emaciation disease. Metagenome results showed that, in addition to olive flounder genes, the myxosporean gene was the most abundant in the intestine and urinary bladder. The results of multiplex PCR assay revealed high levels of detection of E. leei genes in the intestines of samples having a relative condition factor <70% whereas the gene of P. anisocaudata was detected at high levels in the urinary bladders of all sample groups. In addition, statistical analyses indicated a significant association between decrease in relative condition factor and E. leei infection but not P. anisocaudata infection. We suggest that the emaciation disease is caused by E. leei and the parasite decrease relative condition factor to <70%.