Disease mechanisms of emaciation disease of tiger puffer

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1) Parasitological examinations of myxosporeans from the intestine of emaciated tiger puffer were conducted, and morphological characteristics and developmental processes of Myxidium fugu n. sp., Leptotheca fugu n. sp. and Myxidium sp. TP were described. Further, diagnostic procedures of the above myxosporeans were established based on Diff-Quik-stained intestine imprints and HE ＆ Uvitex2B-stained histological sections.2) Histopathological examinations indicated that heavy infections with Myxidium sp. TP or Leptotheca fugu caused exfoliation and degeneration of the intestinal epithelia of tiger puffer, while M. fugu caused no significant damage in the intestinal tissues.3) Myxidium sp. TP and M. fugu transmitted from fish to other fish by feeding the infected tissues, cohabitation with infected fish and exposure to effluent from a tank holding infected fish.4) Kinetics of Myxidium sp. TP were investigated in experimentally infected fish. Development of the parasites was found to be temperature-dependent : They developed at 20C and 25C, while they became "cryptic" at 15C. Experimentally infected fish with Myxidium sp. TP became anorexic from week 3 at 20C, and showed the typical sign of the from week 6 at 20C.5) Moisture absorbance ability of infected fish was significantly lower than that of uninfected fish, indicating that functions of osmotic regulation were hampered in diseased fish. Further, atrophy of the liver and reduced hepatic indicators (LDH, GOT and GPT) of infected fish suggested that emaciated fish had a functional disorder in the liver.6) The causative organisms of emaciation disease of tiger puffer were demonstrated to be the Intestinal myxosporeans, Myxidium sp. TP and Leptotheca fugu. Modes of transmission and developmental kinetics of the parasites were characterized. Heavy infections with the myxosporeans caused a significant disorder in osmotic regulations in the intestine, resulting in the emaciation disease.