| Summary: | The purpose of this study was to examine the impact of immersion in ice water on turbot habituated to higher and lower environmental temperatures (19o C, ‘summer’ and 12 o C, ‘winter’ respectively). Such procedures are commonly used during transport or slaughter, and it is not known whether such rapid cooling will lead to loss of consciousness in fish such as turbot. Six turbot of each treatment (summer, winter water temperature) were subjected to cold water for 1hr and 15min. Behavioural observations focussed on nociceptive stimulation, vibration (tapping) and gill movements. Heart and brain activity (EEG and ECG) was also recorded. Such physiology, supplemented with behaviour, is important to establish potential welfare concerns negatively affecting sustainability of the aquaculture of turbot. No clear differences between treatments were found. Fish responded to immersion with elevated heart activity, and at 2 and 5 min after immersion in ice water a significant reduction in gill movement was found (p < 0.05). The EEG analysis showed a reduction in amplitude, but at t=15 min more than 50% of the fish still showed total power values over 10% of pre-immersion values, and hence unconsciousness could not be established with certainty. More than an hour after immersion in the cold water some turbot still responded to nociceptive stimuli and vibration. Immersion in cold water reduced brain activity, the implication of which is not clear. Several signs of stress were observed, e.g. increased heart beats. We conclude that from a welfare point of view, immersion of turbot in ice water may not be humane.
|
|---|