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Detection and sub-cellular distribution of the amnesic shellfish toxin, domoic acid, in the digestive gland of Octopus vulgaris during periods of toxin absence

Abstract Domoic acid (DA) is a neurotoxin produced by Pseudo-nitzschia diatoms that is accumulated in the highest concentrations in filter-feeding organisms, such as bivalve molluscs. Although DA is a water-soluble molecule that is rapidly cleared from most marine organisms, it appears that octopus may consistently contain DA in the digestive gland. To test this hypothesis, specimens of Octopus vulgaris were caught for DA analysis when Pseudo-nitzschia cells were not observed in seawater and DA was not detected in octopus food items, i.e. mussels. DA was consistently detected in each octopus specimen (n=32) analysed and its concentrations varied from 1.0 to 26.6 µg g−1. DA sub-cellular distribution was evaluated in the digestive gland of six specimens in order to prove whether DA preferably accumulates in some cell compartment. DA was predominantly found (>90%) in the soluble fraction (cytosol) and to a lesser extent in the insoluble fractions (nucleic, mitochondrial, lysosomal, microsomal). This disposition should favour DA trophic transfer from prey to predators. The present study contributes with relevant data to the growing knowledge on the accumulation of marine toxins in cephalopods and on the trophic transfer of DA throughout the marine food web.