R. Hoffmann’s research while affiliated with Technical University of Munich and other places

Different stunning methods for fish (manual stunning - blow on the head, carbon dioxide exposition and electricity) were investigated and compared taking into account both the aspects of product quality and of animal welfare. Besides manual stunning, two commercially available systems were used to anaesthetize trout (Oncorhynchus mykiss, n = 60), catfish (Silurus glanis, n = 60) and flounder (Platichthys flesus, n = 30). Onset and progress of anaesthesia were recorded as well as signs of stress, pain or suffering. Immediately after stunning blood was taken to determine hematocrit values and levels of glucose and cortisol. This was followed by filleting and sensory investigation of the fish. In the case of carbon dioxide exposition, signs of stress, pain or suffering varying in duration and intensity were observed in all investigated species. After stunning was performed manually or by electricity, partly marked reflex movements could be observed. Repetititon of the blow on the head was needed in catfish and sporadically in trout. A repeated stunning process was necessary in 10 % of all trout anaesthetized electrically. Using carbon dioxide exposititon, the average period of time required for anaesthesia was 158 s in trout, 168 s in flounder and 185 s in catfish, respectively. A tendency towards lower values of blood glucose coinciding with higher levels of hematocrit was determined in flounders as well as in trouts stunned manually. Apart from that, the blood parameters obtained after application of different stunning methods showed only slight differences. As far as stress parameters are concerned, a final appreciation of the different methods of stunning is yet not possible. Adverse effects on product quality were solely found in trout stunned electrically. In general, a darker colour of the fillets as well as blood spots due to fractures of ribs and of the spine (30 %) were discernible.

Different stunning methods for fish (manual stunning - blow on the head, carbon dioxide exposition and electricity) were investigated and compared taking into account both the aspects of product quality and of animal welfare. Besides manual stunning, two commercially available systems were used to anaesthetize trout (Oncorhynchus mykiss, n = 60), catfish (Silurus glanis, n = 60) and flounder (Platichthys flesus, n = 30). Onset and progress of anaesthesia were recorded as well as signs of stress, pain or suffering. Immediately after stunning blood was taken to determine hematocrit values and levels of glucose and cortisol. This was followed by filleting and sensory investigation of the fish. In the case of carbon dioxide exposition, signs of stress, pain or suffering varying in duration and intensity were observed in all investigated species. After stunning was performed manually or by electricity, partly marked reflex movements could be observed. Repetititon of the blow on the head was needed in catfish and sporadically in trout. A repeated stunning process was necessary in 10 % of all trout anaesthetized electrically. Using carbon dioxide exposititon, the average period of time required for anaesthesia was 158 s in trout, 168 s in flounder and 185 s in catfish, respectively. A tendency towards lower values of blood glucose coinciding with higher levels of hematocrit was determined in flounders as well as in trouts stunned manually. Apart from that, the blood parameters obtained after application of different stunning methods showed only slight differences. As far as stress parameters are concerned, a final appreciation of the different methods of stunning is yet not possible. Adverse effects on product quality were solely found in trout stunned electrically. In general, a darker colour of the fillets as well as blood spots due to fractures of ribs and of the spine (30 %) were discernible.