Enteromyxum leei (Myxosporea: Bivalvulida) as the cause of myxosporean emaciation disease of farmed olive flounders (Paralichthys olivaceus) and a turbot (Scophthalmus maximus) on Jeju Island, Korea

Abstract

A life-threatening emaciation disease of unknown cause(s) is affecting the farming of olive flounders (Paralichthys olivaceus) and turbots (Scophthalmus maximus) on Jeju Island, Korea. As this is one of the major industries in the region, it is of great concern to local farmers trying to develop successful and sustainable aquaculture. We examined 16 olive flounders and one turbot cultured at three farms located in the southern part of Jeju Island, which manifested moderate to severe emaciation such as thinning of the body with notable appearance of bony ridges of the skull on heads. Fresh mucosal scrapings of the intestinal mucosa contained many myxosporean vegetative stages at various developments but not fully grown spores. Histological examination of gastrointestinal and other visceral organs revealed striking changes in the intestinal mucosa such as detachment and loss of the epithelium due to intensive parasitism of the myxosporean vegetative stages, accompanied by considerable leukocyte infiltration in the lamina propria, and at the final stage villus atrophy with no epithelial lining. Specific polymerase chain reaction using a pair of primers targeting a fragment of the 18S ribosomal RNA gene (rDNA) of Enteromyxum leei, a known pathogen causing myxosporean emaciation disease in a variety of cultured fish in Mediterranean countries and Japan, amplified 433-bp products in almost all diseased fish samples, particularly the gastrointestinal tract. Nearly the whole length of the 18S rDNA, 1672-bp long excluding primer-aligning sequences, of the present Korean isolate was comparable to those of E. leei isolates from Japan and Europe, particularly those from the former region. Taking the heavy load of various developmental stages of E. leei in the gastrointestinal mucosa into account, we ascribe the emaciation disease of the fish examined in the present study to this well-known myxosporean species and not to another unknown pathogen(s).

Quantitative investigation of Enteromyxum leei (Myxozoa: Myxosporea) infection and relative condition factor in cultured olive flounder Paralichthys olivaceus (Temminck and Schlegel)

“…Recent studies have identified that E. leei is the causative agent of emaciation disease that has caused great economic loss to the cultured olive flounder industry in Korea, especially in Jeju Island (Sekiya et al, 2016;Shin et al, 2018). In addition, Yasuda et al (2005) In the present study, there was no mortality or signs of emaciation in any of the groups until 6 weeks post-inoculation.…”

“…Recent studies have identified that E. leei is the causative agent of emaciation disease that has caused great economic loss to the cultured olive flounder industry in Korea, especially in Jeju Island (Sekiya et al., ; Shin et al., ). In addition, Yasuda et al.…”

“…Since the first detection of emaciation disease in cultured olive flounder of Korea, several studies have been performed to verify its aetiological agent, pathophysiological mechanism and clinical features (Choi et al., ; Kim, Jun, Park, Jeong, & Jeong, ; Kim et al., ; Sekiya et al., ). Interestingly, a Korean research group reported that a Parvicapsula anisocaudata caused emaciation in cultured olive flounder in Korea (Kim et al., ) whereas a Japanese research group identified E. leei as pathogen of the emaciation disease (Sekiya et al., ) even though these two studies investigated olive flounder produced in the same region (Jeju Island). Recently, we revealed that E. leei is a causative agent of emaciation disease in cultured olive flounder using molecular diagnostics (Shin, Sohn, Jin, Kang, & Lee, ).…”

“…The production of fish comprises 50% of finfish culture. Since the first detection of emaciation disease in cultured olive flounder of Korea, several studies have been performed to verify its aetiological agent, pathophysiological mechanism and clinical features (Choi et al, 2012;Kim, Jun, Park, Jeong, & Jeong, 2015;Kim et al, 2011;Sekiya et al, 2016).…”

“…Interestingly, a Korean research group reported that a Parvicapsula anisocaudata caused emaciation in cultured olive flounder in Korea (Kim et al, 2015) whereas a Japanese research group identified E. leei as pathogen of the emaciation disease (Sekiya et al, 2016) even though these two studies investigated olive flounder produced in the same region (Jeju Island). Recently, we revealed that E. leei is a causative agent of emaciation disease in cultured olive flounder gated the parasite intensity in the posterior intestine of the fish.…”