Depuration of Okadaic acid (Diarrhetic Shellfish Toxin) in mussels, Mytilus edulis (Linnaeus), feeding on different quantities of nontoxic algae

Abstract

Depuration of mussels contaminated by Diarrhetic Shellfish Toxins (DST) is a potential option for the shellfish industry to manage the impact of DST. Field observations have suggested that the main factor regulating the rate of depuration of DST is the quantity of nontoxic algae available for the mussels to feed upon. In this paper, the effects of the quantity of food, which mussels feed upon, on the rate of depuration of DST in Mytilus edulis L. was tested in a laboratory experiment. Mussels naturally contaminated by the DST okadaic acid (OA) were collected from a mussel farm located on the Swedish west coast during a bloom event. Individual mussels were placed in filtered seawater and given daily rations of a mixture of nontoxic algae as follows: no food, 0.5% and 1.5% of dry weight body mass day −1. Depuration was performed over 1, 2, 4, 8, 16 or 32 days. The levels of OA decreased in all treatments with time, with an average of approximately 50% reduction after 32 days. No significant differences in content of OA among food rations were detected. In contrast to predictions, a trend towards lower levels of toxins in the mussels receiving no food compared to both food treatments was observed after 32 days of depuration. The loss of toxins in mussels that were not feeding correlated with a considerable loss in the mass of the digestive gland between 16 and 32 days. It was concluded that the rate of depuration of OA in mussels is not positively correlated with digestive activity and fecal production. Instead, the lipophilic character of the OA molecule suggests that OA may have affinity for lipid-rich cellular and intracellular components. Increased usage of lipid stores, which occur during starvation, may accelerate the release of OA. This model could explain the observations made during the last part of this experiment. In management of toxic mussels, depuration in waters free of toxic algae is not likely to be enhanced by increasing the food supply to mussels; however, long periods of depuration in the absence of food should be avoided because of the negative effects on the condition of the mussels.