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actaAdriat47(1).indd ISSN: 0001-5113 AADRAY ACTA ADRIAT., 47 (1): 79 - 83, 2006 UDC:597.587.2:639.32](261.1):595.12 595.12:[597.587.2:639.32](261.1) Short communication Hepatoxylon trichiuri (Cestoda: Trypanorhyncha) plerocercoids in cage-reared northern bluefin tuna, Thunnus thynnus (Osteichthyes: Scombridae) Ivona MLADINEO Institute of Oceanography and Fisheries, P.O. Box 500, 21000 Split, Croatia e-mail: [email protected] Northern bluefin tuna (Thunnus thynnus) were caught by purse seine boats and brought to a farm for a rearing cycle of 1.5 years. Mortalities occurred in the first weeks of acclimatization at the facility. Parasitological examination revealed plerocercoids of the cestode Hepatoxylon trichiuri embedded in the stomach mucosa. The larvae were found in 28.4% of the fish and the mean abundance was 3.12 per fish. Histopathology revealed disseminated erosion at the site of attachment, atrophy of fundic glands, lymphocytic migration, and hyperplasia of connective tissue in the lamina propria. These symptoms, however, together with the parasite abundance, could not have triggered the mortalities. This is the first record of this parasite in northern bluefin tuna. Key words: histopathology, bluefin tuna, Hepatoxylon trichiuri, Cestoda INTRODUCTION Cage rearing of northern bluefin tuna (Thun- nus thynnus) in the Adriatic Sea is a relatively recent and growing type of aquaculture. Tuna are caught from the wild and raised intensively in floating semi-offshore cages for six months to 1.5 years. Fish are fed fresh anchovies and other mixed small pelagic fish or frozen imported her- rings. Mortality is usually observed during the acclimatization period and is presumed to be due to the lengthy transportation and handling period during transfer to the cages. Sudden or severe changes in abiotic parameters such as temperature, weather conditions, and oxygen also can induce mortality and, so far, only a small proportion of mortalities in farmed

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