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DAO 64:127-134 (2005)
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Abstract
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Role of cellular response in elimination of the monogenean Neoheterobothrium hirame in Japanese flounder Paralichthys olivaceus
Chihaya Nakayasu1,*, Nobuyuki Tsutsumi2, Norihisa Oseko3, Satoshi Hasegawa4
1Inland Station, National Research Institute of Aquaculture, Fisheries Research Agency, Tamaki, Mie 519-0423, Japan
2Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of
Tokyo,Yayoi 1-1-1, Bunkyo, Tokyo 113-8657, Japan
3National Research Institute of Aquaculture, Fisheries Research Agency, Nansei, Mie 519-0193, Japan
4Graduate School of Marine Science and Technology, Tokyo University of Marine
Science and Technology,Tokyo 108-8477, Japan
*Email: cnakayas@fra.affrc.go.jp
ABSTRACT: Adult worms of the blood-feeding monogenean parasite Neoheterobothrium hirame, which cause anemia in the Japanese flounder Paralichthys olivaceus, attach to the host fish by embedding their posterior part deeply into the host
tissue. To investigate the possibility that cellular responses of the host fish can eliminate N. hirame, flounder were experimentally infected with N. hirame larvae and reared in either fed or starved conditions. Mature parasites were
identified on the buccal cavity wall of the fish 33 d post-infection (Day 33). Monocytes/macrophages and granulocytes increased rapidly in the blood and infected sites after the appearance of mature parasites. These cells adhered to the tegument of the
parasites. In addition, a few cells with large electron-dense granules (DGCs) were observed in the inflammatory foci. On Day 47, the tegument of some parasites collapsed partially and were phagocytosed by the infiltrated host cells. Some infiltrated cells
adhered directly to the inner tissues of the parasites. On Day 54, in the fed fish group, the loss of the tegument led to damage of the parasites’ inner tissue by a large number of infiltrated cells. In this group, the elimination of the parasites
was noted from Day 47 to 54. These observations probably suggest that the cellular response of the host fish destructed the parasite’s posterior part embedded in the tissue, thereby eliminating the parasites. On the other hand, a high mortality was
observed in the starved group. The starved fish developed much more severe anemia than the fed fish, and the elimination of the parasites was not observed in this group. The results of the present study suggest that flounder can eliminate N. hirame
if they are fed sufficiently.
KEY WORDS: Flounder · Leucocytes response · Neoheterobothrium hirame · Monogenean parasite
Full text in pdf format
Published in DAO Vol.
64, No. 2
(2005) on April 18
Print ISSN: 0177-5103; Online ISSN: 1616-1580.
Copyright © Inter-Research, Oldendorf/Luhe, 2005
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