Óleo essencial de Mentha piperita (Lamiaceae) no controle de monogenoideas das brânquias de Arapaima gigas (Arapaimidae)

Abstract

This study aimed to investigate in vitro efficacy of Mentha piperita essential oil in control of monogenoideas Arapaima gigas gills and to evaluate the toxicity and histological effects of this natural product for this fish. For in vitro assay, A. gigas naturally infested by Dawestrema cycloancistrium and Dawestrema cycloancistrioides were used and collected its gills and exposed to 0, 80, 160 and 320 mg/L of essential oil M. piperita. The results showed that all these in vitro concentrations tested were effective (100%) against Dawestrema spp. from gills of A. gigas. Acute toxicity test was performed using 168 A. gigas fingerlings, distributed in 14 tanks (12 fish/tank) and exposed 0, 20, 40, 80, 100, 130, 160 mg/L of M. piperita essential oil. The results of toxicity test were calculated using Trimmed Spearman Karber method and showed that the lethal concentration (CL50-4h) was 38 mg/L. There were differences in the mortality of fish in relation to the concentrations used in the acute toxicity test. The first gill arch right of fish exposed to the essential oil of M. piperita were used and processed for histological analysis by the usual methods (fixation in 10% buffered formalin, decalcification, dehydration, embedded in paraffin, cut of 6 microns) and stained with hematoxylin-eosin. There was not tissue changes in gills of fish of the control group and those exposed to 20 and 40 mg/L the essential oil of M. piperita, while in fish exposed to 80, 100, 130 and 160 mg/L occurred elevations epithelial, fusion of secondary lamellae, hypertrophy and aneurysm, but necrosis occurred only when 160 mg/L essential oil of M. piperita was used. The essential oil of M. piperita has anthelmintic activity and was toxic to A. gigas in the highest concentrations tested. Thus, therapeutic baths may be made using essential oil of M. piperita only in concentrations around 20 mg/L