Welfare aspects of live chilling and freezing of farmed eel (Anguilla anguilla L.): neurological and behavioural assessment
Firstly, 19 eels with an average live weight of 758±44 g were restrained and equipped with EEG, ECG electrodes and a temperature sensor inside the body. Then, they were placed in the ice water. Indices for the induction of unconsciousness and insensibility were the appearance of theta and delta wave...
| Published in: | Aquaculture |
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| Main Authors: | , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2002
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| Subjects: | |
| Online Access: | https://research.wur.nl/en/publications/welfare-aspects-of-live-chilling-and-freezing-of-farmed-eel-angui https://doi.org/10.1016/S0044-8486(02)00050-9 |
| Summary: | Firstly, 19 eels with an average live weight of 758±44 g were restrained and equipped with EEG, ECG electrodes and a temperature sensor inside the body. Then, they were placed in the ice water. Indices for the induction of unconsciousness and insensibility were the appearance of theta and delta waves and no response on pain stimuli, which disappeared at a body temperature of 8.0±2.1 °C after 12±5 min in 15 eels. The responses to pain stimuli did not disappear in three eels. Within a confidence level of 95°the percentage of eels that is not effectively stunned during the procedure in ice water of <5 °C was at least 5ÐThe heart rate decreased from 24±10 beats/min (n=14) to 7±4 (n=11) and became irregular during cooling down. When placed in the brine water of -18 °C, the EEG showed rapid and extreme depolarisation of the membranes, which started after 27±17 s (n=18). The ECG showed fluttering of the heart in all eels. None of the eels recovered after this procedure. For 10 eels with an average live weight of 128±27 g, it was observed that the body temperature decreased from 17.1±0.6 to 4.0±0.5 °C in the ice water. After 15 min in the brine water of -16.1±2.2 °C, the body temperature decreased to -3.1±2.3 °C. Finally, three groups of seven eels and eight single eels were placed in ice water of -0.0±0.1 °C. The observation of unrestrained eels revealed four phases. Animals were (1) swimming around in the water, (2) attempting to escape from the ice water, (3) pressing their nose to the wall or corner while showing clonic muscle cramps, and finally (4) breathing only, while all other muscle activity was totally suppressed. Afterwards, they were transferred to cold brine at -18 °C, and none of the eels recovered. The eight control eels, which were transferred to water at 18 °C, swam around, except for one that was lying in an S-shape position at the bottom. After 570 and 605 s, two eels tried to escape from the box. The obtained results show that the eels, which were transferred from water at 18 °C to ice water, ... |
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