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This study evaluated the effect of short‐term baths with the essential oils (EOs) of Lippia sidoides, Ocimum gratissimum and Zingiber officinale on the survival, haematological, biochemical and histopathological parameters of native fish tambaqui (Colossoma macropomum), challenged with Aeromonas hydrophila. After challenge, the fish infected with A. hydrophila received therapeutic baths of 60 min, for five consecutive days. Treatments were as follows: challenged and not treated; challenged and treated with 10 mg L−1 of gentamicin; challenged and treated with EO of L. sidoides (2.5 and 5.0 mg L−1); challenged and treated with EO of O. gratissimum (5.0 and 10.0 mg L−1); challenged and treated with Z. officinale EO (5.0 and 10.0 mg L−1). The highest survival rates were 89.5% (fish treated with 5.0 mg L−1 of O. gratissimum EO) and 75.0% (fish treated with 5.0 mg L−1 of L. sidoides EO). Reductions in the haematocrit percentage, haemoglobin and erythrocyte number were observed in fish treated with L. sidoides and Z. officinale EOs compared with control fish. Mild to moderate damage to the liver tissue of fish after challenge and EO treatments were observed. It is suggested that baths containing O. gratissimum and L. sidoides EOs consist in a viable treatment to increase survival rates of C. macropomum infected with A. hydrophila. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the antimicrobial activity of the essential oils from five Brazilian Piper species (Piper aduncum, Piper callosum, Piper hispidinervum, Piper hispidum and Piper marginatum) against strains of Aeromonas hydrophila, isolated from tambaqui (Colossoma macropomum), as well as their chemical composition. The oils were characterized by gas chromatography and mass spectrometry (GC/MS), and the major compounds identified were: dillapiole (80.7 %) for P. aduncum; safrole (67.0 %), methyl-eugenol (7.2 %) and β-pinene (6.6 %) for P. callosum; safrole (89.3 %) for P. hispidinervum; γ-terpinene (27.3 %), p-cymene (14.0 %) and α-terpinene (12.0 %) for P. hispidum; δ-3-carene (13.1 %), propiopiperone (8.0 %) and (E)-caryophyllene (6.8 %) for P. marginatum. The Brazilian Piper species evaluated in this study were able to inhibit the growth of the ten strains of A. hydrophila, with minimum inhibitory concentration (MIC) values ranging from 234.37 to 30,000 μg mL-1. The antimicrobial activity of Piper essential oils was considered strong for P. callosum, P. hispidinervum, P. hispidum and P. marginatum, with the exception of P. aduncum that presented weak activity for all strains. This is the first record of antimicrobial activity of Piper essential oils against strains of A. hydrophila isolated from tambaqui, suggesting the potential for use in the treatment of infections caused by this bacterium. [ABSTRACT FROM AUTHOR]