Unconsciousness assessment through electroencephalography (EEG), in the process of stunning for humane slaughter of Nile tilapia

Author(s)

Daniel Santiago Rucinque

• Document type: Doctoral Thesis
• Press: Pirassununga.
• Institution: Universidade de São Paulo (USP). Faculdade de Zootecnica e Engenharia de Alimentos (FZE/BT)
• Defense date: 2021-01-27

Examining board members

Elisabete Maria Macedo Viegas; Tatiana Emanuelli; Dariane Beatriz Schoffen Enke; Judite das Graças Lapa Guimarães; Giuliana Parisi

• Advisor: Elisabete Maria Macedo Viegas

Abstract

Chapter 1 presents a brief introduction to the subject and the aim of these. Chapter 2 assessed Ocimum americanum (OA) or Lippia alba (LA) essential oils as anaesthetics in Nile tilapia and their influence on the aroma. For the anaesthetic evaluation, Nile tilapia were divided into four groups: ethanol (ET), 2-phenoxyethanol (PE), Ocimum americanum (OA) or Lippia alba (LA), all at 500 µL/L. OA or LA essential oils at 500 µL/L were effective in inducing deep anaesthesia with unconsciousness duration of 126 s, allowing time for bleeding. Anaesthesia with Ocimum americanum or Lippia alba essential oils may be indicated as an alternative to hypothermia at pre-slaughter handling of fish in Brazil. Chapter 3 aimed to assess mechanical spiking and electrical stunning as methods to induce unconsciousness in Nile tilapia, and their effects on rigor mortis. Nile tilapia were divided into three groups, two groups for spiking and one group for electrical stunning. Mechanical spiking with lateral access is effective to induce unconsciousness without recovery, delaying the onset of rigor mortis in Nile tilapia, thus its use in an automatic system could be an alternative to traditional slaughter of hypothermia in Brazil. Chapter 4 aimed to assess unconsciousness using electroencephalography EEG in Nile tilapia under different methods at pre-slaughter. Nile tilapia were divided in five different methods at pre-slaughter: anaesthesia with phenoxyethanol at 1 mL/L (PE), anaesthesia with Ocimum americanum (OA) or Lippia alba (LA) essential oils at 500 µL/L, spiking (SP) and hypothermia in ice/water (2:1). The median time (s) to lose consciousness as represented by the suppressed phase was PE (136 ± 61), OA (171 ± 164), LA (171.5 ±77.8) and HP (252 ± 752) (P<0.01). Spectral analysis suggested unconsciousness after 3 minutes of exposure to PE, OA or LA due to the decreases in Ptot, F50 and F95, and also the increase in contribution from the delta frequency and decrease in contribution from the beta frequency. The values obtained in the spectral analysis for fish submitted to HP suggest that this method does not induce unconsciousness. When used in Nile tilapia, phenoxyethanol-like anaesthetic showed both EEG traces and spectral analyses consistent with unconsciousness after 140 s of immersion. Anaesthesia with 500µL/L of the essential oils Ocimum americanum or Lippia alba induced unconsciousness after 180 s of immersion, as determined by EEG. The use of hypothermia at pre-slaughter of Nile tilapia does not induce unconsciousness and should be urgently substituted by methods that meet criteria of humane slaughter. Chapter 5 assessed the influence of different pre-slaughter methods: hypothermia live chilling (HP); anaesthesia with the essential oils Ocimum americanum (OA) or Lippia alba (LA) and mechanical spiking (SP) on the meat quality parameters of Nile tilapia stored under refrigeration for 15 days. The use of mechanical spiking and anaesthesia with the Ocimum americanum (OA) or Lippia alba (LA) essential oils in Nile tilapia did not negatively change the following quality parameters of the meat: pH value, rigor mortis, TVB-N and K-value as compared to the traditional method of hypothermia. (AU)

• FAPESP's process: 17/15364-9 - UNCONSCIOUSNESS ASSESSMENT THROUGH ELECTROENCEPHALOGRAFY (EEG), IN THE PROCESS OF STUNNING, FOR ElECTRONARCOSIS, PERCUSSION AND ANESTHESIA FOR HUMANE SLAUGHTER OF NILE TILAPIA
• Grantee: Daniel Santiago Rucinque Gonzalez
• Support Opportunities: Scholarships in Brazil - Doctorate