Key words: Myxozoa, Enteromyxum, tiger puffer, epizootiology

The effect of water temperature on the development of enteric myxozoans causing myxosporean emaciation disease of cultured tiger puffer

Tetsuya Yanagida (1)*, Hiroshi Yokoyama (1) and Kazuo Ogawa (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
yanagi-t@wg7.so-net.ne.jp

Myxosporean emaciation disease, caused by the enteric myxozoans, Enteromyxum leei and Leptotheca fugu, is a serious problem in Japanese farmed tiger puffer, Takifugu rubripes. We conducted epizootiological surveys of enteric myxozoans at four geographically different areas where tiger puffer were cultured. Using a PCR-based, non-lethal diagnostic method, we found that the prevalence of infection with E. leei increased up to 65-100% between autumn and early winter and declined in mid-winter, while the seasonal pattern of L. fugu was not clear. At one site, which had a noticeably lower water temperature as compared to the remaining three sites, the prevalence of E. leei was considerably lower (< 30%). We then examined the effect of water temperature on the development of E. leei in experimentally infected fish. Naïve tiger puffer maintained at 20C were fed gut tissue infected with E. leei. They were then separated into different tanks and kept at different constant temperature classes, ranging variously from 10C to 25C. The results demonstrated the suppressive effects of low water temperature (<15 C) both on the development of E. leei and on the onset of disease. The present study indicates that occurrence of the emaciation disease of cultured tiger puffer are associated with ambient water temperature.