Effects of toxic dinoflagellates and toxin biotransformation in bivalves

Attempts were made to elucidate the different responses of shellfish to paralytic shellfish poison (PSP) and the PSP donor Alexandrium minutum T1. Five species of edible bivalves (Crassostrea gigas, Meretrix lusoria, Mytilus edulis, Ruditapes philippinarum, and Soletellina diphos) were collected and examined for susceptibility to PSP and PSP donor. It was determined that all five bivalves had low susceptibility to PSP following an intramuscular injection (> 300 MU/20 g). The abnormal effects on bivalves were species-specific and varied with the concentration of A. minutum T1. Judging from the LC50 data (medium lethal concentration), the resistance of bivalves to the toxic dinoflagellate was as follows (least to most resistant): C. gigas < R. philippinarum < M. lusoria < M. edulis, S. diphos. With the exception of S. diphos, the bivalves accumulated very little toxin (< 2 MU/g edible tissue) when they were exposed to 10(7) cells/L of A. minutum for four days. The toxin levels in S. diphos increased with exposure time to the toxic dinoflagellates and accumulated primarily in the digestive gland (88-100%), followed by the gill (0-10%), and other organs (0-8%). Although the concentrations of toxin components in the digestive gland were found to be variable during the exposure period, the toxin profile in the digestive gland of S. diphos during the early exposure period was similar to that of A. minutum. Moreover, toxin components in the gills and in other organs were retained at near constant concentrations during the exposure period.