Ocimum americanum and Lippia alba essential oils as anaesthetics for Nile tilapia: Induction, recovery of apparent unconsciousness and sensory analysis of fillets

In Brazil, humane slaughter regulations do not include fish, and hypothermia or immersion in ice water is used in most fish slaughterhouses for pre-slaughter handling. Such a method is not considered humanitarian as it does not induce an immediate loss of consciousness and fish show aversive behaviour when immersed in a water and ice mixture. This study aimed to assess the times for induction and recovery using Ocimum americanum and Lippia alba essential oils as anaesthetics in Nile tilapia, and their influence on the flavour and aroma of fillets. For the anaesthetic evaluation, Nile tilapia (224.05 +/- 67.56 g, 22.10 +/- 2.41 cm) were divided into four groups (40 fish/group): ethanol (ET), 2-phenoxyethanol (PE), Ocimum americanum (OA) and Lippia alba (LA), all at 500 mu L/L. The times taken to reach total loss of equilibrium, anaesthesia and consciousness recovery were recorded using a stopwatch. Blood was collected from the caudal vein after 0, 1, 4, 8 and 24 h of anaesthesia for the analysis of glucose, lactate and cortisol. For the sensory analysis, fillets from fish exposed to essentials oils and hypothermia at pre-slaughter were evaluated by 122 untrained assessors to determine differences in the aroma and flavour attributes. The induction of deep anaesthesia (stage 4) was faster in the OA group (mean +/- standard error of mean SEM) (126.8 +/- 4.9 s), than the PE (152.3 +/- 6.6 s) and LA groups (169.7 +/- 10.9 s) (p < .01). A total of 91.7% (110/120) of the fish showed VOR (Vestibulo-Ocular Reflex) as the first behavioural response during consciousness recovery after anaesthesia. The levels of glucose (mmol/L) were similar amongst the groups at each time. The lactate levels (mmol/L) were higher at 0 h of sampling in LA (2.0 +/- 0.2) than in ET (1.4 +/- 0.8) (p < .05) and the cortisol levels (ng/mL) at 0 h were higher in ET (150.3 +/- 55.3) than in OA (33.9 +/- 9.7). Fillets prepared from Nile tilapia anesthetized using OA essential oil received higher sensory scores (1.5 +/- 0.1) than fillets from both the Lippia alba (1.0 +/- 0.1) and control groups (0.7 +/- 0.1). OA and LA essential oils at 500 mu L/L were effective in inducing deep anaesthesia with unconsciousness duration of 126 s, allowing time for bleeding. Anaesthesia with Ocimum americanum and Lippia alba essential oils may be indicated as an alternative to hypothermia for the pre-slaughter handling of fish in Brazil.

Automated summary

This study assessed the use of Ocimum americanum and Lippia alba essential oils as anaesthetics in Nile tilapia, showing that Ocimum americanum oil induced deep anaesthesia faster than Lippia alba oil and resulted in higher sensory scores for fillets. The essential oils were effective in inducing deep anaesthesia, providing a potential alternative to hypothermia for fish pre-slaughter handling in Brazil.