Veterinary Immunology and Immunopathology 157 (2014) 142–148 Contents lists available at ScienceDirect Veterinary Immunology and Immunopathology j ourna l ho me pag e: www.elsevier.com/locate/vetimm Research paper The use of eugenol against Aeromonas hydrophila and its effect on hematological and immunological parameters in silver catfish (Rhamdia quelen) Fernando Jonas Sutili a , Luiz Carlos Kreutz b , Mirela Noro b , Leticia Trevisan Gressler c , Berta Maria Heinzmann d , Agueda Castagna de Vargas c , Bernardo Baldisserotto a,∗ a Departamento de Fisiologia e Farmacologia, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil b Faculdade de Agronomia e Medicina Veterinária, Universidade de Passo Fundo, 99052-900 Passo Fundo, RS, Brazil c Departamento de Medicina Veterinária Preventiva, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil d Departamento de Farmácia Industrial, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil a r t i c l e i n f o Article history: Received 26 September 2013 Received in revised form 18 November 2013 Accepted 30 November 2013 Keywords: Aeromonas Innate immune system Fish Silver catfish Bacteria Hematology a b s t r a c t The aim of this study was to evaluate the activity of eugenol against the fish pathogen Aeromonas hydrophila and eugenol’s effect on hematological and natural immune param- eters in silver catfish (Rhamdia quelen). In vitro, eugenol showed weak activity against A. hydrophila, but in vivo, at a subinhibitory concentration (10 mg L -1 ), it promoted sur- vival in infected silver catfish. Eugenol (50 g mL -1 ) reduced the hemolytic activity of A. hydrophila supernatant in vitro in fish erythrocytes. Subjecting catfish to eugenol baths (5 and 10 mg L -1 ) for five days did not alter the hematological and immunological parame- ters studied in this work. Based on these results, eugenol can be used to treat or prevent bacterial diseases in fish. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Medicinal plants and their active compounds have been widely used in veterinary and human medicine and currently play a significant role in aquaculture (Direkbusarakom, 2004). These products present antimi- crobial potential and they can be used as prophylactic and therapeutic agents against fish pathogens (Citarasu, 2010) or as immunostimulants that confer early activation on the non-specific defense mechanisms of fish (Harikrishnan et al., 2011). The therapeutic use of essential oils, extracts ∗ Corresponding author. Tel.: +55 55 3220 9382; fax: +55 55 3220 8241. E-mail addresses: bbaldisserotto@hotmail.com, bernardo@smail.ufsm.br (B. Baldisserotto). and isolated compounds from plants in the treatment of diseases or as immune response modulators in fish can be accomplished by baths (Harikrishnan et al., 2003) or by incorporation into feed (Pachanawan et al., 2008). Eugenol is the major component (70–90%) of clove oil (Keene et al., 1998) and is found in several other plant essential oils. In aquaculture, eugenol and clove oil have been used and recommended as an alternative anesthetic for several fish species (Javahery et al., 2012). In addition, the low cost of obtaining eugenol, as well as its antimi- crobial potential (Filgueiras and Vanetti, 2006; Qiu et al., 2010), further promote its use in aquaculture. Eugenol has attracted the attention of researchers because of its chemo- preventive effects as well as its anti-inflammatory and anti-oxidant properties (Yogalakshmi et al., 2010; Leem et al., 2011). 0165-2427/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.vetimm.2013.11.009