Manabu Asakawa has expertise on biotoxins of hydrosphere accumulated over many years. He discovered toxic substance responsible for the food poisoning due to ingestion of gallbladders of cyprinid fish. He concluded that the structure of carp toxin to be 5α-cyprinol sulfate (5α-cholestane-3α, 7α, 12α, 26, 27-pentol 26-sulfate).