Comparative study on the esterification of gymnodimine in different shellfish exposed to the dissolved toxin in seawater.

Some lipophilic phycotoxins dissolved in seawater can be accumulated by bivalves via the filtering process. To explore the relationship between the bioaccumulation of gymnodimine-A (GYM-A) and free fatty acids (FFAs) of shellfish, three species of bivalves (venus clam Meretrix meretrix, mussel Mytilus galloprovincialis, and ark shell Anadara kagoshimensis) were exposed to dissolved GYM-A for 7 days in the same seawater system. Results indicated that GYM-A can be accumulated by these bivalves from the dissolved phase and esterified with FFAs reaching over 90% in most tissues of bivalves. Gymnodimine-A and its esters mainly distributed in the gills of shellfish, and the highest concentration of toxins occurred in mussel, followed by ark shell and venus clam. Similar percent of different fatty acid esters occurred in the experimental shellfish, in which the C16:0, C17:0, C18:0, C18:1, C20:1, C20:2, C22:2, and C22:6-GYM-A esters were the main metabolites of GYM-A. The binding capacity of fatty acids and GYM-A varied in different FFAs, which can explain why the C20:1-GYM-A ester dominated the ester profile while C16:0 was the most abundant fatty acid in all samples. Comparing with the FFA profile of shellfish in the control groups, overexpression of some FFAs occurred in the tissues of shellfish exposed to GYM-A in the experimental groups, which suggested that biosynthesis of FFAs was affected by the accumulation and metabolism of GYM-A in bivalves. Multiple fatty acids including some valuably nutritional FFAs such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were consumed in the esterification metabolism of GYM-A, which hinted that the lipid metabolism and nutritional quality of shellfish affected by the contamination of GYMs should be explored and assessed in future works.