Eighteen lumpfish (Cyclopterus lumpus), which were bred in an aquarium, exhibited skin ulceration approximately 280 days after their arrival in our facility. Gross observations in necropsy revealed the presence of round yellow to pale brown granulomas in muscle, gill, liver, spleen, kidney, stomach, testis, and ovary, with obvious distension and foci of necrosis in kidney. Microscopic examination of the lesions showed numerous hyphae in squash preparations and histology. The colony morphology of the fungus at the incubation on potato dextrose agar with chloramphenicol at 25 degrees appeared woolly and velvety, and brownish black in color. Molecular sequence analysis of the internal transcribed spacer regions of ribosomal RNA genes demonstrated Exophiala sp. As such, fish with fungal infection in their skin ulceration by microscopy were isolated.
Abdominal ultrasonography was also performed on fish without skin ulceration. Fish with regional hypoechoic lesions, diffused strong echo and acoustic shadow noted in various coelomic viscera, were also isolated. Necropsy of the deceased isolated fish diagnosed by ultrasonography showed lesions in viscera similar to Exophiala sp. infected fish, with results further confirmed by microscopy. No symptom was noted in the 4 fish with Exophiala infection confirmed negative by inspection and ultrasonography.
Exophiala spp. are ubiquitous in soil and aquatic environments and are often considered as environmental contaminants,1 which could cause infection locally and systemically.2 Exophiala infection was also confirmed in the lumpfish kept at their original aquarium. Thus, this mass infection should be caused by the induction of the infected fish. Present study results by inspection, ultrasonography and necropsy demonstrated that Exophiala infected viscera, leading to the lesion formation, and eventually observable skin ulceration. Some Exophiala infections were found in both fish and humans;3 opportunistic infection, in particular, occurred in immunosuppressed patients.4,5 Attention should therefore be paid on any Exophiala infection as a zoonosis in the aquarium. It appears that ultrasonography for diagnosing Exophiala infection is effective for their quarantine, husbandry management and prevention of the zoonosis.
The authors would like to thank Syuji Sodeyama and Kohei Noma for their assistance to keep the lumpfish.
* Presenting author
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