Fish-to-fish Transmission of Myxidium spp. (Myxozoa) in Cultured Tiger Puffer Suffering from Emaciation Disease

Experimental transmission of Myxidium fugu and Myxidium sp. TP (formerly described as Myxidium sp. in tiger puffer Takifugu rubripes) among tiger puffer was successful by the following 3 methods; 1) feeding infected gut tissue, 2) cohabitation with infected fish, 3) exposure to effluent from a tank containing infected fish. Regardless of the transmission methods, prevalences of infection in the intestine with M. fugu reached 100%. However, those with Myxidium sp. TP, which is suspected of an etiological agent of the emaciation disease, varied among experiments conducted in different months, suggesting that development of Myxidium sp. TP was strongly influenced by the ambient temperature. It was evident that trophozoites of Myxidium sp. TP excreted from the infected fish were transmittable directly to other fish. Mortalities and morbidities in fish experimentally infected with Myxidium sp. TP seemed to be associated with the parasite's development which might be promoted by higher temperature. The present study suggests that fish-to-fish transmission of Myxidium spp. occurs in sea cages, inducing a rapid spread of the emaciation disease among farmed tiger puffer.