ABSTRACT: A syndrome characterized by atypical swimming behaviour followed by rapid death was first reported in captive southern bluefin tuna Thunnus maccoyii (Castelnau) in the winter of 1993. The cause of this behaviour was found to be a parasitic encephalitis due to the scuticociliate Uronemanigricans (Mueller). Based on parasitological and histological findings, it is proposed that the parasites initially colonise the olfactory rosettes and then ascend the olfactory nerves to eventually invade the brain. Possible epidemiological factors involved in the pathogenesis of the disease include water temperature (<18°C) and the immune status of the fish.

KEY WORDS: Southern bluefin tuna · Thunnus maccoyii · Scuticociliate · Uronema nigricans ·Encephalitis · Neuritis

Published in DAO Vol. 30, No. 1 (1997) on July 24
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1997