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. leei infection in cultured olive flounders in Korea. To reveal a relationship between E. 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. 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. leei was detected at levels greater than 10 cells/L in the culture water where enteromyxosis occurred from July to September. Furthermore, 2 months after the detection in the water, the parasite gene (with more than 5,000 cells per 100 mg) was detected in fish intestine samples. However, in the fish farms where enteromyxosis had not occurred, the E. leei gene was detected at <10 cells in culture water (1 L) and fish intestine samples (100 mg). The quantification method used in this research provides a baseline of the infection timeline in olive flounder to develop effective management practices.

Comparison of specificity and sensitivity of diagnostic methods for Enteromyxum leei and Enteromyxum fugu detected from cultured tiger puffer, Takifugu rubripes in Korea

“…There are four species of Enteromyxum genus, Enteromyxum leei , Enteromyxum scophthalmi , Enteromyxum fugu and E. caesio ; these myxosporean parasites are known causative agents of enteromyxosis and emaciation disease in fishes such as Takifugu rubripes (tiger puffer), Pagrus major (red sea bream), Oplegnathus punctatus (Spotted knifejaw), Scophthalmus maximus L. (turbot) and Paralichthys olivaceus (olive flounder) (Freeman et al, 2020; Palenzuela et al, 2002; Sohn et al, 2021; Tun et al, 2002; Yanagida et al, 2004; Yanagida et al, 2008). Myxosporean emaciation disease causes serious problems such as weight loss and tapering body signs of severe emaciations and intestinal inflammation, which lead to low food conversion rates and eventually death in infected fish (Ogawa & Yokoyama, 2001; Sitjà‐Bobadilla & Palenzuela, 2012).…”

“…Therefore, myxosporean infection control strategies are primarily preventative and effective management techniques, which involve lowering fish density and improving water quality (Fontes et al, 2015). Thus, early infection diagnosis is essential to control the disease (Sohn et al, 2021). However, owing to the lack of sufficient number of pathogens in the early stages of infection in fish, the DNA concentration of pathogens extracted from the primary target organ is low; therefore, a highly sensitive method is required for early diagnosis, rendering one‐step PCR method insufficient.…”