Search

Simple Summary: The World Organization for Animal Health recommends the use of stunning methods before the slaughter of farmed fish destined for human consumption. The use of carbon dioxide (CO2) is not recommended by the World Organisation for Animal Health for the stunning of farmed fish at pre-slaughter. However, its use continues to be common in the world. CO2 stimulates chemoreceptors, causing aversion and escape attempts when fish are immersed in CO2-saturated water. The use of CO2 in seawater with oxygenated water is allowed for pre-slaughter of halibut in Norway. Hence, there are no studies assessing loss of consciousness in halibut exposed to this stunning method. The best approach to determine unconsciousness is by measuring brain electrical activity through EEG. As fish welfare becomes a growing concern, it is important to ensure humane treatment during slaughter. This study aimed to assess the onset of unconsciousness in Atlantic halibut immersed in CO2-saturated seawater through electroencephalography (EEG). Of the 29 fish studied, 10 exhibited escape attempts, indicating aversion to CO2-saturated water despite its oxygenation. EEG signals showed four distinct phases: transitional, excitation (high amplitude–high frequency), suppressed, and iso-electric phases. The onset of the suppressed phase, indicative of unconsciousness, occurred on average 258.8 ± 46.2 s after immersion. The spectral analysis of the EEG signals showed a progressive decrease in median frequency, spectral edge frequency, and high frequency contribution, which corresponded to the gradual loss of consciousness. The study concludes that CO2-saturated water is not recommended for pre-slaughter handling of halibut due to the extended time required for the onset of unconsciousness and the observed aversive behaviour. Ensuring humane treatment during slaughter is important for addressing public concern and safeguarding fish welfare in all stages of production. [ABSTRACT FROM AUTHOR]

The short‐ and long‐term effects of altered photoperiods during winter on growth and final gonadosomatic index (GSI) were investigated in 178 individually tagged 2‐year‐old smolt Arctic charr from an anadromous strain. The fish were reared at ambient temperature (2.3–12.5°C) for 18 months and reared at five different photoperiods. One group was reared on constant LD16:8 (light–dark, N = 40) photoperiod and a second group on continuous light (LD24:0, N = 32) throughout the experimental period. Three groups of fish were moved from LD16:8 to LD24:0 for 44 days and subsequently back to LD16:8, that is early winter light group (Early WL: 17 November–5 January; N = 35), Mid WL group (5 January–23 February; N = 38) and Late WL group (23 February–6 April; N = 33). No differences in growth were found for females, whereas males reared at constant LD24:0 were larger (mean ± SEM, 1,780 g ± 180) compared with the Late (1,264 g ± 101) and Mid WL (1,413 g ± 120) groups towards the end the study. Exposure to continuous light during early winter significantly influenced the GSI in female Arctic charr, whereas no differences were found in the males. Female GSI (%) was lowest in the Mid WL group (1.7) and highest in the LD24:0 group (7.0). In conclusion, the present study demonstrated that application of brief continuous light treatments during January and February can possibly be used as a tool to lower subsequent female maturation in Arctic charr farming. [ABSTRACT FROM AUTHOR]

In the present study, selected temperature drops were examined to investigate the effects of live chilling on stress and welfare in turbot and sole. This study demonstrated that rapid temperature drops from 11°C-12°C and 18°C-18.7°C to 4°C-0°C in turbot resulted in higher blood sodium and potassium at 0°C (164 mmol l−1, 4.4 mmol −1) compared to 4°C (153 mmol l−1, 3.1 mmol −1), indicating osmoregulatory disturbance. A rapid temperature drop from 18°C to 0°C in Senegal sole also resulted in higher blood sodium and potassium at 0°C (164 mmol l−1, 4.8 mmol −1) compared to the control group at 18°C (157 mmol l−1, 3.2 mmol −1). Based on present findings, we conclude that immersion in ice water will have a negative effect on the animal osmoregulatory capacity, and we recommend that turbot and sole are stunned before slaughter. [ABSTRACT FROM AUTHOR]