Three myxosporeans and 2 hyperparasitic microsporeans were found in the intestine of emaciated cultured tiger puffer Takifugu rubripes in Kyushu district of Japan. Morphology of the 3 myxosporeans were examined and described as Myxidium fugu n. sp., Leptotheca fugu n. sp. and unidentified Myxidium sp. Spores of M. fugu n. sp. having 2 club-shaped polar capsules were bean-shaped, 14.0 (13.5-15.5) μm in length and 9.0 (8.0-10.0) μm in width. Spores of L. fugu n.sp. having 2 spherical polar capsules were trapezium-shaped, 9.0 (8.3-9.5) μm in length and 14.0 (13.0-15.0) μm in thickness. Their piscine intestinal developmental stages were illustrated and arranged in a hypothetical developmental sequence. Plasmodia of M.fugu n. sp. were located on the epithelium of intestine, whereas those of L. fugu n. sp. and Myxidium sp. were found intercellularly in the intestinal epithelium. Only a few mature spores could be observed in these myxosporeans, but the differences in stainability by Diff-Quik and Uvitex 2B and in location of development made it possible to differentiate the species. Two hyperparasitic microsporeans were often found in the plasmodia of M. fugu n. sp. and L. fugu n. sp, but their pathogenic effects to host myxosporeans were unclarified.