Paralytic shellfish toxins (PSTs) are potent neurotoxins produced by a variety of marine dinoflagellates, such as . PSTs can accumulate and be passed into the food chain through the filter feeding of toxin-producing algae by bivalve mollusks. The consumption of contaminated shellfish can cause poisoning in humans, with symptoms including nausea, vomiting, diarrhea, numbness or tingling in the extremities, and even death as a result of respiratory failure. is widely distributed along the coast of China, and often forms large algal blooms in the waters surrounding Nanhuangcheng Island, the Zhoushan area, and the port city of Xiamen. Many controlled feeding experiments with shellfish have investigated the accumulation and fate of PSTs toxins in the marine food web. Comparative studies of PST profiles often found significant differences between the causative dinoflagellates and contaminated bivalve mollusks, thus indicating active metabolism of the toxin in some shellfish. The scallops are known to become much more toxic for consumption than mussels grown under the same environmental conditions, and several months are required until the toxicity drops to an acceptably safe level. Conversely, levels of toxicity in the short-necked clam and oysters are generally low, and the toxicity can decline as quickly as in the mussel. The metabolic interconversion of incorporated toxins achieved by enzymatic and chemical reactions in the tissues of bivalves, and different uptake and depuration kinetics of the individual toxins, may each contribute to differences in the PST profiles.In this study, we exposed scallop directly to toxin-producing algae in order to characterize the formation of PSTs in . Furthermore, we followed PST accumulation and metabolic biotransformation in different organs of the scallop using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The results showed that the AT5-3 strain of in separate areas of the South China Sea were stable both in their growth and toxin production. The composition of the toxin consisted mainly of gonyautoxin-1 and-4, with a cell toxin-production of 7.95 fmol/cell. Rapid accumulation of the PST was observed, while total accumulation efficiency reached 84.4%. The highest accumulation concentration was 1903 μg STX.2HCl-eq/kg. The toxin-accumulation ability of the different tissues was ordered as viscera>gonad>pallium>muscle. Moreover, the viscera showed the strongest PST metabolic ability and was also the target organ. In addition, the proportion of PST in bivalves differed from the profile of the dinoflagellate that produces the toxins. has a strong ability to perform biological transformation. The main transformation pathway was: N-sulfocarbamoy­lgonyautoxin-2 (C1) → gonyautxin-2 (GTX2)/decarbamoylgonyautoxin-2 (dcGTX2), and N-sulfocarbamoylgony­autoxin-3 (C2) → gonyautxin-3 (GTX3). In this experiment, showed characteristically rapid PST-accumulation and slow PST-metabolism; meanwhile the high ratio of the toxin component GTX1 and 4 and NEO resulted in significantly increased risk of PSTs in this scallop. This study contributes to the scientific evaluation of the formation mechanisms of PSTs, thereby providing scientific support for the monitoring of PSTs in China.