Effects of subchronic exposure to glyphosate in juvenile oysters (Crassostrea gigas): From molecular to individual levels

•Sub-lethal effects were studied in juvenile oysters exposed to glyphosate for 56days.•Glyphosate exposure slightly affected condition index, reproduction and tissue alterations.•No dose–response effects were recorded in biochemical endpoints after glyphosate exposure.•GST, MT and MXR mRNA levels were moderately increased by glyphosate exposure. Glyphosate-based herbicides are extensively used and can be measured in aquatic ecosystems, including coastal waters. The effect of glyphosate on non-target organisms is an issue of worldwide concern. The aim of this study was to investigate the effects of subchronic exposure to glyphosate in juvenile oysters, Crassostrea gigas. Yearling oysters were exposed to three concentrations of glyphosate (0.1, 1 and 100μgL−1) for 56days. Various endpoints were studied, from the individual level (e.g., gametogenesis and tissue alterations) to the molecular level (mRNA quantification), including biochemical endpoints such as glutathione-S-transferase (GST) and catalase activities and malondialdehyde content. No mortality and growth occurred during the experiment, and individual biomarkers revealed only slight effects. The levels of gene expression significantly increased in oysters exposed to the highest glyphosate concentration (GST and metallothioneins) or to all concentrations (multi-xenobiotic resistance). These results suggested an activation of defence mechanisms at the molecular level.