Abstract
Recently a mortality has occurred in sea bass, Lateolabrax japonicus, transferred from Korea and cultured at a fish farm in Goto, Nagasaki Prefecture. The main symptoms of this disease are circular swimming movement, whirling and extremely swelled air bladder. The results of bacteriological observations were negative. However, a myxozoan spores was found in every parts of the brain of the fish. They were characterized by the six to eight polar capsules (Fig. 1). Trophozoites were not observed. It closely resembles to Hexacapsula neothunni ARAI and MATSUMOTO, 1953 found in a jellied condition of the body muscles in yellowfin tuna, Thunnus albacores, but can be distinguished from it by the number and size of polar capsules and the site of infection.
Later, the identical spores were also found in the brain of the other marine cultured fish, Japanese striped knifejaw, Oplegnathus fasciatus and yellowtail, Seriola quinqueradiata.
