Electroencephalogram (EEG) assessment of brain activity before and after electrical stunning in the Nile crocodile (Crocodylus niloticus)

Abstract

Electrical stunning is used to capture crocodiles to perform routine management procedures. It is essential from a welfare point that electrical stunning must cause unconsciousness in animals. However, there is no information of whether or not electrical stunning causes unconsciousness in the Nile crocodile (Crocodylus niloticus). The purpose of the study was to assess brain activity before and after electrical stunning in crocodiles using a 5-channel referential electroencephalogram analysis to determine consciousness. Behavioural indicators and electroencephalogram recordings of 15 captive-bred crocodiles were captured and analysed using power spectral density analysis immediately before and after stunning and then at 60 s intervals until 5 min post-stunning. A standardised stun of 170Volts was applied for 5–7 s on the wetted neck. Unconsciousness was defined as a decrease in alpha wave power and increase in delta wave power. Three of the electroencephalograms could not be assessed. Unconsciousness was identified in 6 out of 12 crocodiles and lasted for an average for 120 s. An increase in electroencephalogram waveform amplitude and tonic–clonic seizure-like waveform activity and behaviour indicators were not reliable indicators of unconsciousness. Further research should be focused on improving the efficiency and reliability of electrical stunning.