Objective: Evaluation of Tagetes minuta L. essential oil (EOTM) toxicity in the silver catfish Rhamdia quelen.Methods: The EOTM extracted by hydrodistillation was identified qualitatively based on retention indices and the mass spectrum of its components by gas chromatography-mass spectrometry (GC-MS) and quantified by GC with flame ionization detector. Fish were exposed to 0, 50, 100, 200 mg l-1 EOTM and ethanol (1.5 ml) (n = 10 each concentration) and mortality observed after 24, 48 and 96 h (h).Results: The EOTM presented as the main constituents: di-hidrotagetone (7.66 %), Z-tagetone (29.50%) and E-tagetone (40.37%). Silver catfish mortality was 10% after 96 h at 50 mg l-1, 70 and 80% after 24 and 96 h, respectively, at 100 mg l-1 and 80, 90 and 100% after 24, 48 and 96 h, respectively, at 200 mg l-1.Conclusion: The use of EOTM is not recommended in fish farming at the concentrations measured in this study due to its toxic action.Keywords: Medicinal plants, Fish farming, Toxic effect, Cloves marigoldÂ
