Antiparasitic activity of Mentha piperita (Lamiaceae) essential oil against Piscinoodinium pillulare and its physiological effects on Colossoma macropomum (Cuvier, 1818)

Dinoflagellate infections are a limiting factor in the culture of tambaqui (Colossoma macropomum), especially on the early developmental stages, causing economic losses to producers. To minimize the damage, the essential oils (EO) have been tested and nowadays are considered a promising alternative treatment against pathogens. The objective of this study was to evaluate the efficacy of Mentha piperita (peppermint) essential oil to reduce the number of dinoflagellate Piscinoodinium pillulare in tambaqui juveniles, as well as its influence on the physiology of the fish. For the toxicity test, 192 tambaqui juveniles were subjected to 10 different concentrations of M. piperita EO. The lethal concentration (LC₅₀-4 h) was determined as 79.54 mg L⁻¹. Based on these results, three concentrations were defined and tested as antiparasitic immersion baths. For these in vivo experiments, 150 fish infected by the dinoflagellate were randomly distributed in tanks and subjected to five different treatments: control, control + ethyl alcohol, and three concentrations of M. piperita EO (10, 20, and 40 mg L⁻¹) during 3 days using 10-min baths at 24-h intervals; three replicates per condition. At the end of the therapeutic baths, parasitological and physiological analyses were performed. The M. piperita EO had a parasite removal efficacy of 63.22% and 42.97% (using 20 mg L⁻¹) and 79.91% and 54.56% (40 mg L⁻¹) on the body surface and gills, respectively. Blood analysis found that there was a significant decrease (p < .05) in neutrophils and a significant increase (p < .05) in thrombocytes at concentrations of 20 and 40 mg L⁻¹ when compared to the control fish. Plasma analysis showed a decrease (p < .05) in glucose values when fish were exposed to concentrations of 20 and 40 mg L⁻¹. Based on our results, the concentration of 20 mg L⁻¹ of M. piperita EO was able to reduce the parasitic burden of P. pillulare without causing significant physiological changes.