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Fish welfare quality as affected by pre-slaughter and slaughter management

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. A reliable assessment of animal welfare-suffering and of its impact on product quality requires a multidisciplinary approach that takes into account fish behaviour and the different biochemical and physiological processes involved. This might be done by the contemporary study of changes of indicators of brain function, endocrine responses, post mortem tissue biochemical processes and quality changes. This work reviewed some of the most used indices of stress at the time of slaughter, commercial slaughter methods and related stress effects on physical and biochemical parameters of fish quality. The set of the available data seemed to indicate that, although of some results appear contradictory, pre-slaughter and slaughter stressful practices could have an important effect on the flesh quality in fish. A clear effect emerged mostly on the physical properties of flesh, because severe stress at slaughter time exhausted muscular energies, produced more lactic acid, reduced muscular pH, increased the rate of rigor mortis onset. In this way they could have significant negative effects on technological traits, flesh quality and keeping quality of fish. Asphyxia and electrically stunned fish were more stressed than spiked, knocked and live chilled fish. Combining various methods together might be a more satisfactory strategy for both animal welfare and product quality.
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... We observed positive correlation between rigor mortis and pH changes in fish fillets. It was reported that asphyxia and electrically stunned fish were more stressed than spiked, knocked and live chilled fish (Poli et al. 2005). Therefore, it may be recommended that killing fish by spiking might be a more satisfactory strategy for both animal welfare and product quality. ...
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... Increasing consumer concerns about the quality, safety, freshness and health value aquaculture products have been pushing farmers into becoming increasingly aware of fish welfare and on how intimately connected it is with final product quality [1,2]. Fish health is compromised by several external and internal factors that often occur in a persistent manner throughout the production cycle. ...
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The natural presence of opportunistic pathogens in aquatic rearing systems in alignment with favorable conditions (compromised fish immune status and/or inappropriate rearing conditions) might result in serious acute disease episodes that can develop into chronic immune responses. The present study characterizes molecular, cellular and humoral markers of chronic inflam- mation in a fish species with high commercial value. The intense recruitment of immune cells to the inflammatory focus 21 days after triggering an immune response illustrates a clear chronic character. The cellular response was also noticed with circulating leukocyte numbers rising in the blood of the inflamed fish. Furthermore, the cellular-mediated respiratory burst peaked at 21 days post-injection, suggesting that phagocytes were still actively fighting the inflammatory agent. Regarding the molec- ular analysis, certain genes appear to be good markers of a chronic inflammation response due to their importance in pathways with high relevance in chronic inflammation settings. The present study can serve as a baseline to assess long-term immune-related responses in future studies.
... From an animal welfare perspective, the onset of unconsciousness is absolutely critical (Gräns et al., 2016;Poli et al., 2005;Retter et al., 2018;. Additionally, it is equally important to ensure that the fish remains unconscious long enough to avoid recovery before subsequent death. ...
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Both percussive and electrical stunning have been highlighted as methods that can be used to quickly render fish unconscious before being killed. However, accurately assessing unconsciousness in animals following stunning remains challenging, and thus methods for reliable interpretation and validation of different stunning methods are urgently needed. Here, we used a non-invasive technique to continuously record electroencephalograms (EEG) of rainbow trout (Oncorhynchus mykiss) enabling us to compare the effects of both percussive stunning, using a captive bolt gun, and various combinations of electrical stun parameters delivered in water. The EEG signals were assessed for the absence or presence of an epileptic-like seizure and for visually evoked responses (VERs). No epileptic-like seizures or VERs were observed after captive bolt stunning. We found that it is possible to reliably induce an epileptic-like seizure and an immediate, but short lasting, loss of VERs following a 1 s exposure to an electrical field strength of at least 2.8 VRMS cm⁻¹ and current density of 0.22 ARMS dm⁻² in water of conductivity of ~1000 μS cm⁻¹ using a 50 Hz AC current. However, to avoid recovery of VERs shortly after the stun, it was necessary to increase the duration of the stun application (≥30 s), the electrical field strength (10.2 VRMS cm⁻¹) and the current density (0.84 ARMS dm⁻² respectively). We found no clear relationship between presence and absence of ventilation and VERs following electrical stunning in rainbow trout, highlighting that loss of ventilation may not be a good indicator of brain failure in rainbow trout. Our results clearly show that the presence of an epileptic-like seizure following an electrical stun does not guarantee a prolonged period where the fish is unresponsive to visual stimulation (i.e. absence of VERs). It was further found that VERs can return before the end of the seizure. As both presence of a seizure and absence of VERs have been used independently as indicators of unconsciousness in fish, we emphasize the necessity to carefully consider and evaluate the reliability of neurophysiological indicators of unconsciousness when validating methods to stun fish.
... Additionally, as the slaughter procedure was the same in all animals, the difference in the decreases of the pH values in time can be explained by the stress of spawning. In comparison to the described prolonged stress, acute stress increases muscle actions and activates anaerobic glycolysis, which would result in a much lower initial pH value [29]. Content courtesy of Springer Nature, terms of use apply. ...
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Pikeperch (Sander lucioperca) is a freshwater fish that has become increasingly popular as a food fish. Within this study, the influence of the spawning process on meat quality was investigated. For this purpose, adult pikeperch was examined directly before and after spawning, and compared regarding physical meat parameters and lipid composition. The results indicate that after spawning, the values of the pH, the electrical conductivity and the yellowness value of fillet were significantly higher than those of the animals sampled before spawning. Analysis of the sum of the total lipid content indicates no differences before and after closed season, but differences in the fatty acid profile were present. Despite significant lower MUFA concentrations, the EPA and DHA showed unaffected high contents. Therefore, the fish muscle indicated an equivalent meat quality. Nevertheless, the significant changes of some physical meat quality parameters after spawning season could have a particular impact on the shelf life and storage of the pikeperch fillet, highlighting the need for further research.
... A variety of biochemical measurements are used as indicators of stress in fish. Among the most frequently measured variables, there are levels of circulating corticosteroid hormones (mainly cortisol) and glucose, lactate, haemoglobin, proteins and haematocrit (Poli et al., 2005). In addition, some components of innate immune system (e.g. ...
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... This is of concern for marine resource management as any resulting mortality may be unaccounted for in stock assessment (Gilman et al., 2013), as well as being ethically unjustifiable. For retained catches, stressors can result in undesirable flesh quality consequences (Poli et al., 2005) that may reduce the value of catches (Sogn-Grundvåg et al., 2021 and references therein). A reduction in stress during capture may therefore promote not only individual fish welfare but also lead to greater sustainability in marine resource management and increased profitability for the industry. ...
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