Due to eutrophication of freshwaters, the frequency of cyanobacteria proliferations is increasing worldwide. From 40 to 75% of cyanobacterial blooms produce hepatotoxins [e.g. microcystins (MCs)], endotoxins released in water during the cell lysis and which constitute a real threat for target organisms as gastropods (intoxication by absorption of toxic cyanobacteria or dissolved toxins). MCs mainly accumulate in the liver (or digestive gland) of metazoans where they interact reversibly (free MCs) or irreversibly (covalently bound MCs) with phosphatase proteins, leading to tissues destruction. We previously demonstrated that the gastropod Lymnaea stagnalis ingested MC-producing cyanobacteria and accumulated free and bound MCs. As bound MCs persisted after a 3-week depuration period and represented up to 90% of total MCs, L. stagnalis is potentially potentiallya MC-vector through the food web. The aim of this study is to evaluate if free and bound MCs accumulated in L. stagnalis tissues are transferred to the three-spined stickleback, Gasterosteus aculeatus, and what are the consequences on this latter in terms of: 1) MC accumulation and elimination, 2) histopathology of the liver, 3) oxidative stress response, and 4) behavioural changes. Fish accumulated MCs (up to 3.9 +- 0.1 micro g g-1 DW) in the liver, kidneys, muscles, and gills, showed an increased activity of glutathione peroxidase in the liver associated with a moderate pathology, and a decrease of the locomotory activity. During depuration, from 92 to 100% of free MCs were eliminated in all organs excepted in muscles (from 6 to 58%), suggesting that MC accumulation in G. aculeatus after consumption of intoxicated gastropods may induce a second transfer in aquatic and terrestrial food web, and possibly a human contamination.