Effects of Antifouling Biocides on Molecular and Biochemical Defense System in the Gill of the Pacific Oyster <i>Crassostrea gigas</i>

<div><p>Antifouling biocides such as organotin compounds and their alternatives are potent toxicants in marine ecosystems. In this study, we employed several molecular and biochemical response systems of the Pacific oyster <i>Crassostrea gigas</i> to understand a potential mode of action of antifouling biocides (i.e. tributyltin (TBT), diuron and irgarol) after exposure to different concentrations (0.01, 0.1, and 1 μg L^-1) for 96 h. As a result, all the three antifouling biocides strongly induced the antioxidant defense system. TBT reduced both enzymatic activity and mRNA expression of Na⁺/K⁺-ATPase and acetylcholinesterase (AChE). Lower levels of both Na⁺/K⁺-ATPase activity and <i>AChE</i> mRNA expression were observed in the diuron-exposed oysters compared to the control, while the irgarol treatment reduced only the transcriptional expression of <i>AChE</i> gene. We also analyzed transcript profile of heat shock protein (<i>Hsp</i>) superfamily in same experimental conditions. All antifouling biocides tested in this study significantly modulated mRNA expression of <i>Hsp</i> superfamily with strong induction of <i>Hsp70</i> family. Taken together, overall results indicate that representative organotin TBT and alternatives have potential hazardous effects on the gill of <i>C</i>. <i>gigas</i> within relatively short time period. Our results also suggest that analyzing a series of molecular and biochemical parameters can be a way of understanding and uncovering the mode of action of emerging antifouling biocides. In particular, it was revealed that Pacific oysters have different sensitivities depend on the antifouling biocides.</p>