Limites de segurança e aplicação anestésica do óleo essencial de Dizygostemon riparius em Tambaqui e sua relação com o perfil químico dos constituintes voláteis

Abstract

The use of anesthetics in aquaculture is important to reduce stress and minimize physical damage to fish during management procedures such as biometrics, transportation, marking, and biological sampling, contributing to animal welfare. In this context, natural compounds such as essential oils have been investigated as possible alternatives. Dizygostemon riparius, known as “melosa”, is an aromatic species belonging to the Plantaginaceae family and endemic to the state of Maranhão, Brazil, whose essential oil remains little explored regarding its applications in aquaculture. Thus, the objective of this study was to chemically characterize the essential oil of Dizygostemon riparius and evaluate its behavioral effects and acute toxicity in juveniles of Colossoma macropomum from different size classes. The essential oil was obtained by hydrodistillation of the leaves and characterized by gas chromatography coupled with mass spectrometry (GC–MS), allowing the identification of 32 constituents, with predominance of oxygenated monoterpenes. The major compounds were endo-fenchyl acetate (42.66%) and endo-fenchol (34.88%), which together represented more than 70% of the total oil composition.Toxicological evaluation revealed a response dependent on concentration and fish size. In smaller fish (≈3.3 g), acute toxicity was observed from approximately 46.9 mg·L−1, with total mortality at concentrations close to 70 mg·L−1. In larger fish (≈15 g), no mortality was observed under the evaluated conditions. In behavioral assays, the essential oil produced concentration-dependent sedative and anesthetic effects: concentrations between 75 and 100 mg·L−1 were associated with sedation, while approximately 120 mg·L−1 induced anesthesia, with shorter induction times as dose increased and longer recovery times at higher concentrations. These results indicate dose- and body size-dependent responses and suggest an association between the chemical profile of the oil and the observed effects. The conclusions of this study are limited to the evaluation of acute toxicity and behavioral parameters, and further studies including subchronic or chronic toxicity, pharmacokinetics, residue analysis, histopathological, reproductive, and environmental assessments are required for a broader evaluation of the applicability of D. riparius essential oil in aquaculture.