Anatoxin-a is a cyanobacterial neurotoxin with a worldwide occurrence in freshwater ecosystems. As a result of global climate changes, it is expected to occur an increase of eutrophication processes and of frequency and intensity of cyanobacterial blooms in several regions of the world. In these conditions, the water concentrations of cyanotoxins, including anatoxin-a, may increase reaching toxic levels, with an additional risk for organisms able to bioconcentrate it in their body. Considering the importance that these processes may have in freshwater ecosystems and the lack of knowledge that still exists on the topic, this study tested the hypothesis that rainbow trout is able to bioconcentrate anatoxin-a. A 96 h bioassay was carried out by exposing juvenile fish to three concentrations of anatoxin-a (132 ug/L, 264 ug/L and 524 ug/L) through the test media. At the end of the assay, the actual concentrations of the toxin were determined in the test media and in the whole fish body by HPLC-FLD and the bioconcentration factors (BCF) were determined. At all the tested concentrations of anatoxin-a, the fish body concentrations of the toxin were higher than the corresponding water concentrations, with BCF ranging from 30 to 47 based on fresh weight. These findings indicate that the rainbow trout is able to bioconcentrate anatoxin-a, even during short-term exposures and this process may considerably increase the risk of being intoxicated in real scenarios. Since other species of fish may have also this capability and considering that they are key species in a considerable number of freshwater ecosystems, more research should be done on this most important topic in the actual context of global climate changes.