Influence of gametogenesis pattern and sex on paralytic shellfish toxin levels in triploid Pacific oyster Crassostrea gigas exposed to a natural bloom of Alexandrium minutum

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Journal Article
Aquaculture, 2016, 455 pp. 118 - 124
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© 2016 Elsevier B.V.. This study investigated the effect of gametogenesis pattern and sex on levels of paralytic shellfish toxins (PST) accumulated by triploid oysters Crassostrea gigas exposed to a natural bloom of the toxic dinoflagellate Alexandrium minutum in the Bay of Brest (Western Brittany, France), over the summer 2014. Toxin accumulation in oysters was proposed to be influenced by the proportion of energy allocated to reproduction versus other metabolisms, as proposed by Haberkorn et al. (2010). Thus, we hypothesized that triploid oysters with different gametogenesis patterns (α or β, producing respectively numerous gametes or rare gametes) could result in differences in toxin accumulation. Toxin level could also be different according to the gender of the oysters. To test these hypotheses, PST levels were measured in the digestive gland of oysters using an ELISA method. Sex, gametogenesis stage and pattern (α or β) of the triploid oysters were determined by histology. Males (24%), females (38%) and hermaphrodites (38%), including synchronous or successive hermaphrodites were represented among the sampled oysters. All of them were at mature stage (III) of gametogenesis. Both α (46%) and β (54%) patterns were represented in the sample set. In these oysters, PST levels appeared independent from sex and gametogenesis pattern. These results suggest that, in triploid oysters, PST accumulation is not influenced by energy allocated to reproduction. Statement of relevance: This study appears to be the first to investigate toxin levels depending on gametogenesis pattern in triploid oysters.This study highlighted that triploid oysters were divided into two classes, α (triploid oysters that maturate with unlocked germ cells and have a consequent number of gametes) and β (triploid oysters that display strongly reduced number of gametes and locked gonial mitosis), with the latter class subdivided into two categories: β1, which presents no germinal cell lineage, and β2, which presents germinal cell lineage.This study showed that toxin levels in the digestive glands of triploids were not significantly different, neither between gametogenesis patterns nor between sexes. Additionally, despite the different patterns of gametogenesis in the triploid oysters of the present study, no difference in toxin levels accumulated in the digestive glands was detected between α and β oysters, suggesting that reproductive investment in triploid oysters does not influence toxin accumulation.
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