It was examined whether the common belief that "cultured puffer fishes do not contain tetrodotoxin (TTX)", the major lethal substance that accidently causes death in consumers of those fishes, is true in river puffer fish Takifugu obscurus. In mouse bioassay, lethal levels of toxins were detected in the ranks: gonad>liver>intestine>muscle>skin in wild puffer fish. In contrast, no mortality occurred in the mouse bioassay on cultured fish. However, there were sleepiness, sluggish behavior, and hind limb paralysis with the tissue extracts of cultured fish suggesting the presence of TTX or other similarly acting toxins. An attempt to confirm the presence of TTX in cultured fish with high performance liquid chromatography (HPLC) was not very successful. The results suggest possible existence of TTX toxins or similarly acting toxins.