Anesthesia and anesthetic action mechanism of essential oils of Aloysia triphylla and Cymbopogon flexuosus in silver catfish (Rhamdia quelen).

OBJECTIVES

To document the time for anesthesia induction and recovery using different concentrations of essential oils (EOs) of Cymbopogon flexuosus and Aloysia triphylla in silver catfish (Rhamdia quelen), and to determine whether the mechanism of action of either EO involves the benzodiazepine (BDZ) site of the GABA receptor.

STUDY DESIGN

Experimental study.

ANIMALS

A total of 144 silver catfish, length 7.5 ± 1.1 cm, weighing 3.95 ± 0.85 g.

METHODS

Essential oils were evaluated at concentrations of 25, 150 and 300 μL L, and also ethanol alone (seven groups, n = 6 per group). Induction of sedation or anesthesia and recovery were assessed. In a further six groups (n = 6 per group), fish were exposed to both EOs (25, 150 or 300 μL L) with diazepam 150 μm, and also diazepam (10 μm) alone. Flumazenil (5 or 10 μm) was added to the recovery water of fish exposed to diazepam (150 μm) or both EOs (150 and 300 μL L) (total of 10 groups = 60 fish).

RESULTS

Both EOs induced anesthesia at concentrations of 150 and 300 μL L, and sedation at 25 μL L. There was no significant difference between EOs for reaching deep anesthesia; there was a significantly longer recovery time for the EO of C. flexuosus. The addition of diazepam (150 μm) resulted in faster induction of anesthesia with both EOs, with no significant change in recovery times. Flumazenil (10 μm) reversed the diazepam-induced anesthesia, but not the anesthesia induced by EOs.

CONCLUSIONS AND CLINICAL RELEVANCE

The EO of C. flexuosus induced effective sedation (25 μL L) and anesthesia (150 and 300 μL L) without short-term mortality. The modulation of the BDZ site of the GABA receptor in the anesthetic action mechanism of both EOs was not demonstrated.