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Diseases of Aquatic Organisms

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DAO 35:31-36 (1999)  -  doi:10.3354/dao035031

Natural mass infection by heterophyid metacercariae in aquacultured Japanese eel in Taiwan

Hong-Kean Ooi1,*, Way-Shyan Wang1, Ching-Yu Tu1, Hong-You Chang2, Cheng-I Chen1

1Department of Veterinary Medicine, National Chung Hsing University, 250 Kuo Kuang Road, Taichung, Taiwan, ROC
2Livestock Disease Control Center of Yunlin County, 517 Section 2 Yunlin Road, Toliu, Yunlin County, Taiwan, ROC

ABSTRACT: A natural mass infection of heterophyid metacercariae in aquacultured Japanese eel Anguilla japonica in Taiwan was observed. Of the 28000 adult eels in 2 ponds, about 25000 (90%) showed swollen, cloudy and white eyes. Although morbidity was about 90%, there was no mortality among the affected eels. Histopathological sections showed edema and hemorrhage of the eye. Numerous metacercariae were observed in the muscle tissues around the eyeball, the subcutaneous tissue and even in the cartilage. Of the 6 eels digested with artificial gastric juice, all were found to contain metacercariae in their muscle tissues. The average number of metacercariae recovered from the 6 eels was 1219, with a range of 50 to 3762. These metacercariae, when fed orally to immunodeficient (scid) mice, developed into adult worms which were identified as Procerovum cheni Hsu 1950. The naturally infected eels were transferred to a new pond without snails and their eye lesions were not apparent anymore after 2 wk. In a follow-up investigation, 19 of 20 apparently healthy eels in a nearby aquaculture farm were found to harbour metacercariae in their muscles. However, the number of the metacercariae ranged from 1 to 14, with an average of 4.21. This is the first report of heterophyid metacercariae causing mass morbidity in aquacultured eels.

KEY WORDS: Eel · Heterophyid metacercariae · Eye lesion · Taiwan · Procerovum cheni

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