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DAO 58:165-170 (2004)
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Abstract
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X-cells in fish pseudotumors are parasitic protozoans
Satoshi Miwa1,*, Chihaya Nakayasu1, Takashi Kamaishi2, Yasutoshi Yoshiura1
1Inland Station, National Research Institute of Aquaculture, Tamaki, Mie 519-0423, Japan
2National Research Institute of Aquaculture, Nansei, Mie 516-0193, Japan
*Email: miwasat@affrc.go.jp
ABSTRACT: Bottom-dwelling teleosts, particularly flatfishes or cod living in temperate to cold seawater, sometimes develop tumor-like lesions on the body surface or in the branchial cavity. These lesions usually contain masses of so called 'X-cells'
of unknown origin. We amplified a gene for small subunit ribosomal RNA (18S rRNA) from X-cell lesions of the flathead flounder Hippoglossoides dubius. Phylogenetic analysis clearly classified the obtained sequence as a protozoan, although the
organism had no clear affinity with any known protistan groups. In situ hybridization showed that probes specific for the protozoan 18S rRNA hybridized only with X-cells, and not with the host-fish cells, indicating that X-cells harbor the
protozoan rRNA. On the other hand, a probe specific for vertebrate 18S rRNA hybridized with the host-fish cells, but not with X-cells. This is conclusive evidence that X-cells are parasitic protozoans.
KEY WORDS: X-cell · 18S rRNA · In situ hybridization · Protozoa · Hippoglossoides dubius · Fishes · Pseudotumor
Full text in pdf format
Published in DAO Vol.
58, No. 2-3
(2004) on March 10
Print ISSN: 0177-5103; Online ISSN: 1616-1580.
Copyright © Inter-Research, Oldendorf/Luhe, 2004
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