<i>Zingiber officinale</i> (Ginger), <i>Curcuma longa</i> (Turmeric) and <i>Cymbopogon nardus</i> (Lemon Grass) Essential Oils Have Anti‐Dactylogyrideans Potential in <i>Colossoma macropomum</i> Cuvier 1816 (Tambaqui)

ABSTRACT Essential oils are composed of secondary metabolites derived from medicinal plants and have bioactive properties, such as antiparasitic activity. This study investigated the in vitro anti‐dactylogyridean efficacy of the Zingiber officinale , Curcuma longa and Cymbopogon nardus essential oils, as well as the acute toxicity for Colossoma macropomum (tambaqui). The majority chemical components of the essential oils of Z. officinale (α‐zingiberene, β‐sesquiphellandrene, limonene and geranial), C. longa (ar‐turmerone, α‐turmerone, α‐phellandrene, curlone and 1,8‐cineole) and C. nardus (geraniol, geranial and neral) were analysed. All the essential oils exhibited dose‐dependent efficacy against dactylogyrideans Anacanthorus spathulatus , Notozothecium janauachensis and Mymarothecium boegeri , and the mean effective concentration (EC 50 ) was 16.6 mg L −1 (3 h and 30 min) for Z. officinale essential oil, 30.9 mg L −1 (2 h and 15 min) for C. longa essential oil and 13.7 mg L −1 (30 min) for C. nardus essential oil. Effects of these oils on the ultrastructure of Anacanthorus dactylogyrideans exposed to the essential oils were also evaluated using scanning electron microscopy. This study shows for the first time the potential use of the Z. officinale , C. longa and C. nardus essential oils in controlling dactylogyridean parasites.