The research was published in the journal Aquatic Toxicology on 26 November 2020. Scientists from the Unit for Viral Diseases in Fish at ANSES's Ploufragan-Plouzané-Niort Laboratory tested the effect of exposure for 10 months to pure glyphosate and two commercial glyphosate-based herbicidal formulations on four-year-old adult rainbow trout. The substance was in a concentration comparable to that found in nature: about 1 µg per litre. No major changes in mortality, reproductive success or metabolism were observed in exposed fish compared to unexposed controls. However, two months before spawning, there was a 70% reduction in the proportion of macrophages – the white blood cells involved in immunity – in trout exposed to either of the two commercial formulations. At the same time, phagocytic activity, a component of the immune response, decreased by 35% for trout exposed to the glyphosate-based herbicides. These effects were not found for trout exposed to pure glyphosate, suggesting that the co-formulants in the herbicides also played a part. Further work will be carried out to better understand this decline in immunity, by assessing the ability of fish to combat infection. The potential impacts of glyphosate, alone or in commercial herbicide formulations, will also be assessed on subsequent generations from the exposed spawners.