Key words: Myxozoa, Kudoa, host response, pathology

Difference in Pathological Effects of Kudoa megacapsula (Myxozoa) between Different Host Fishes

Hiroshi Yokoyama (1)* and Tetsuya Yanagida (1)

1 Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo, Tokyo 113-8657, Japan  ayokoh@mail.ecc.u-tokyo.ac.jp

Kudoa megacapsula (Myxozoa: Multivalvulida) was originally described as the causative agent of post-mortem myoliquefaction of red barracuda (Sphyraena pinguis). The infected red barracuda exhibited typical signs of the disease, i.e., pale multifocal lesions and tissue lysis of host musculature. Histopathological examination showed the liquefactive necrosis of the myofibers associated with liberated spores. Recently, K. megacapsula was found in the somatic musculature of yellowtail (Seriola quinqueradiata) and greater amberjack (S. dumerili), which were cultured in Japan. Parasite foci were recognized usually as ‘black cysts’ in the skeletal muscles. Liquefied regions were only rarely observed. Intact spores of K. megacapsula were detected in 0-year old fishes, however, only polar capsules were found in 1-year old fishes, probably due to degeneration of spore valves. Histopathological observation showed that K. megacapsula were encapsulated by host’s fibroblast layers, resulting in granulomatous inflammation and spore destruction. The present study reveals notable differences in host response to K. megacapsula between red barracuda and Seriola fishes.