Infection dynamics of Enteromyxum leei (Myxozoa, Myxosporea) in culture water and its effects on cultured olive flounder, Paralichthys olivaceus (Temminck & Schlegel).

Abstract

Enteromyxum leei is a causative agent of enteromyxosis, with a wide range of marine fish hosts. Recently, massive morbidity and mortality were caused by E.&#xa0;leei infection in cultured olive flounders in Korea. To reveal a relationship between E.&#xa0;leei abundance in culture water and the occurrence of parasite infection in host fish, we used a quantitative PCR assay targeting the 28S rDNA of E.&#xa0;leei in three fish farms (two where enteromyxosis had occurred and one where it did not) from April to November 2018. The gene of E.&#xa0;leei was detected at levels greater than 10&#xa0;cells/L in the culture water where enteromyxosis occurred from July to September. Furthermore, 2&#xa0;months after the detection in the water, the parasite gene (with more than 5,000 cells per 100&#xa0;mg) was detected in fish intestine samples. However, in the fish farms where enteromyxosis had not occurred, the E.&#xa0;leei gene was detected at <10 cells in culture water (1&#xa0;L) and fish intestine samples (100&#xa0;mg). The quantification method used in this research provides a baseline of the infection timeline in olive flounder to develop effective management practices.