Abstract
Linalool is the main compound of many essential oils and occurs in two isomeric forms: S-(+)- and R-(-)-linalool. This study aimed to determine if linalool isomers have different antimicrobial and anesthetic properties in fish. For this purpose, these compounds were previously isolated from Lippia alba (Mill.)N. E. Brown and Ocimum americanum L. essential oils. Antimicrobial effects were evaluated through the microdilution test against Aeromonas hydrophila, an important fish disease etiologic agent. Induction time until sedation, anesthesia and recovery time were determined in silver catfish (Rhamdia quelen) through bath exposure (60, 180, 300 or 500 μL L-1). The results showed different biological properties for the isomers being S-(+)-linalool the only active against A. hydrophila at 3.2 mg mL-1. The sedation was induced without differences between the compounds, however R-(-)-linalool promoted faster anesthesia. There were no differences regarding the recovery time of the animals exposed to the linalool isomers. Although both S-(+)- and R-(-)-linalool can be used for sedative purposes, their use in A. hydrophila infection is inadvisable due to the high effective concentration. Considering anesthesia as the main objective, the R-(-)-linalool demonstrated clear advantages at lower concentration.
Highlights
In 2010, the world aquaculture production amounted to 79 million tons, worth US$125 billion
Linalool was detected in 46.6% and 46.7% in O. americanum and L. alba essential oils (EO), respectively, by GCMS analysis (Table I)
The chiral gas chromatography (GC) analysis of the racemic mixture enriched with S-(+)-linalool (Fig. 1a) allowed the identification of the second peak as corresponding to this isomer, because its area decreased when the racemic mixture was evaluated alone
Summary
In 2010, the world aquaculture production amounted to 79 million tons, worth US$125 billion. It has been observed a strong and continuous growth in may be adversely affected by stress. Aeromonas hydrophila is an important etiologic agent being responsible for substantial economic losses in fish culture. This Gram-negative bacterium induces a hemorrhagic and ulcerative disease leading to a high mortality rate, besides it increases the susceptibility to other diseases (Boijink and Brandão 2001, Andrade et al 2006). The use of these antibiotics has contributed to the emergence of resistant strains to available drugs (Andrade et al 2006, Barcellos et al 2008)
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