Abstract
The pacific oyster Crassostrea gigas was experimentally exposed to the neurotoxic Alexandrium catenella and a non-producer of PSTs, Alexandrium tamarense (control algae), at concentrations corresponding to those observed during the blooming period. At fixed time intervals, from 0 to 48 h, we determined the clearance rate, the total filtered cells, the composition of the fecal ribbons, the profile of the PSP toxins and the variation of the expression of two α-amylase and triacylglecerol lipase precursor (TLP) genes through semi-quantitative RT-PCR. The results showed a significant decrease of the clearance rate of C. gigas fed with both Alexandrium species. However, from 29 to 48 h, the clearance rate and cell filtration activity increased only in oysters fed with A. tamarense. The toxin concentrations in the digestive gland rose above the sanitary threshold in less than 48 h of exposure and GTX6, a compound absent in A. catenella cells, accumulated. The α-amylase B gene expression level increased significantly in the time interval from 6 to 48 h in the digestive gland of oysters fed with A. tamarense, whereas the TLP gene transcript was significantly up-regulated in the digestive gland of oysters fed with the neurotoxic A. catenella. All together, these results suggest that the digestion capacity could be affected by PSP toxins.
Highlights
Harmful algal blooms (HAB) occur worldwide and have increased in frequency [1]
Oysters (Crassostrea gigas) and mussels (Mytilus galloprovincialis) cultivated in Thau have been frequently contaminated by PSP toxins and have shown toxicity exceeding the sanitary threshold of μg STX equiv/100 g wet weight, which causes frequent farm closures resulting in economic losses
The main objective of the present study was to determine (i) the feeding activity, (ii) the kinetics of toxin accumulation and de novo produced toxins, and (iii) the expression of the key genes implied in the digestive processes encoding for α-amylase A and B, and for triacylglycerol lipase in C. gigas exposed to a toxic strain of A. catenella or a strain of A. tamarense non-producer of PSTs considered as the control
Summary
Since 1988, the French Atlantic coast (Brittany) has known proliferations of the dinoflagellate Alexandrium minutum, a PSP (Paralytic Shellfish Poisoning) toxin producer. Alexandrium catenella, a neurotoxic dinoflagellate, was observed for the first time in 1998 in the French Mediterranean waters, and has been responsible for major blooms (≥1 × 106 cells/L), which developed during spring and/or autumn in the Thau lagoon. Crassostrea gigas, cultivated in the Thau lagoon with an annual production reaching 10,000 tons, is exposed to A. catenella [2]. Within this context, it is necessary to understand the effects of PSP toxins on the digestive physiology and on the metabolic processes occurring in C. gigas tissues
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