Variation and secretion of toxins in gastropod mollusc Niotha clathrata

Nearly 300 specimens of the gastropod mollusc Niotha clathrata were collected in South Taiwan. All specimens were assayed for toxicity by the official method for tetrodotoxin (TTX). The frequency value of toxic specimens in N. clathrata was 30.0%, 68.0% and 80.4% at Anping, Chiating and Tungkang, respectively. The highest lethal potency of a gastropod specimen was 1900 mouse units (MU). The specimens collected from Tungkang showed the highest frequency of toxic specimens and toxicity, followed by those from Chiating and Anping. The specimens collected in autumn and spring showed higher toxicity than those collected in other seasons. Moreover, another 17 specimens of N. clathrata were collected for testing the toxin secretion by electric shock treatment. It is found that the gastropod did not secrete any additional toxin when electric shock treatment was performed twice at approximately 1-hr intervals. The toxicity of secreted toxin was 206 MU.