Despite safety protocols, crude oil extraction and transportation in the Amazon basin has a potential for inadvertent oil spills, which can impact aquatic organisms in local rivers. The objective of this study was to assess the effects of crude oil on juvenile Amazonian fish tambaqui, Colossoma macropomum, at various biological levels. Furthermore, the effect of crude oil on response to alarm substance, an important communication system in fish, was reported for the first time. Fish exposed to crude oil showed a 90 % decrease in their response to alarm substance and a 60 % decrease in swimming activity relative to control fish. Basic hematology was not affected, although an increase of 200 % of DNA damage and an increase of GST activity were observed in animals exposed to crude oil. Inverse correlations were found between genotoxicity end points and behavioral parameters, suggesting that genotoxic end points can also reflect behavioral changes.