Case report
Enteromyxum leei (Myxozoa), a Lethal Intruder of Tropical Pet Fish: First Case in Humphead Wrasse, Cheilinus undulatus (Rüppell, 1835)

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Abstract

The lethal effect of enteromyxosis is recorded for the first time in the humphead wrasse, Cheilinus undulatus, a tropical pet fish. Enteromyxosis was caused by the myxosporean parasite Enteromyxum leei, and the gut was the only tissue affected in this case. Severe enteritis and degeneration of the intestinal mucosa may have caused a digestive function disorder, thereby resulting in the fish's death. The histopathological findings of this case included destruction of normal tissue architecture of the intestinal mucosa, chronic inflammation, and infiltration of mast cells/eosinophilic granular cells, which resembled findings described in other fish that were diagnosed with enteromyxosis. Induced stress by transportation and entrance to a new environment possibly played an underlying role in the virulence of the parasitic infection and associated tissue pathology.

Section snippets

Case History

A humphead wrasse (23 cm, 161 g) arrived at the facilities of the Cretaquarium, the public aquarium of the Hellenic Centre for Marine Research located in Gournes, Crete, Greece. The fish remained alone in a flow-through tank in the quarantine facilities for 11 days before being transferred to the exhibition tank where it died 9 days later. While quarantined, the behavior of the wrasse was monitored on a daily basis. No fecal, skin, or gill examinations were performed. The day before the

Laboratory Evaluation

After the wrasse died a necropsy was performed using standard microbiological, parasitological, and histological procedures. Direct streaking from head and trunk kidney on tryptic soy agar and thiosulfate citrate bile sucrose was performed. Fresh smears from several tissues were made and examined under light microscopy. Staining of dried smears was performed using Giemsa and methylene blue/azure II/basic fuchsin. Tissue samples from spleen, kidney, liver, heart, and intestine were fixed in

Diagnosis

There were no obvious external pathological abnormalities and no gross lesions found on or within the epidermis, gills, or fins. Internally, no ascites or hemorrhage was apparent in major organs (e.g., liver, heart, kidney, spleen) and bacterial cultures were negative for growth on both media types. The parasitological examination of fresh skin, gills, bile, liver and kidney smears/imprints was negative. The intestinal tract showed evidence of a mass infection of a myxozoan resembling the

Discussion

Enteromyxum leei has been previously reported as causing mortalities in L'Aquarium Barcelona, affecting more than 25 fish species; its occurrence was confined to the Mediterranean section.14 However, possible transmission of E. leei to tropical fish should be expected because the pathogen has become established in the tropical marine region of the Red Sea via imported fish culture stocks.17 Moreover, in the early 1980s, Kent identified a myxozoan resembling E. leei in a dying anemone fish,

Acknowledgments

We thank Maria Papadaki for technical assistance in histology and the aquariologists of Cretaquarium.

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