| dc.description.abstract | Atlantic cod is an important species for food production in Norway, and over the last couples of decades; Atlantic cod farming has gradually evolved as an industry in Norway. The harvesting procedures of farmed fish have gained major attention both in the aquaculture industry, research institutions and various organizations dealing with animal welfare issues. According to the legislations, the fish must be stunned before or at the same time as they are killed and remain unconscious until death supervenes. Adequate handling practices, methods of killing, and equipment are therefore needed.
The overall aim of this study was to propose a ‘best practice’ processing line for stunned, bled, gutted, and chilled farmed Atlantic cod, which allows for good fish welfare, low handling stress, efficient bleeding, effective chilling, and maintenance of the intrinsic product quality as produced by farming. Different stunning and killing methods were tested: electrical stunning, AQUI-STM anaesthesia, percussion stunning and carbon dioxide sedation with or without live chilling. Fish welfare and stress response of Atlantic cod exposed to the different stunning/killing methods were studied. Fish quality was assessed post rigor to assess possible connection between stunning methods and quality of the product.
According to the EEG and ECG measurements, both AQUI-STM anaesthesia (68 ml/l,) or euthanasia, electrical stunning in seawater (170 Hz 33% duty cycle) and electrical stunning in air (107 Vrms for 15 sec) proved to be efficient stunning methods for cod. The fish can be rendered unconscious for a prolonged period of time. Doses of > 30 ml/l AQUI-STM should be used for batchwise stunning of cod. Live chilling without an anaesthetic cannot be used as a sedation method for Atlantic cod. Furthermore, live chilling in seawater slurry cannot be recommended, since strong aversive reactions occurred immediately after transfer to the chilling tank. Carbon dioxide sedation at medium levels (245-284 mg/l) might be applicable as a potential sedation method for cod. At lower carbon dioxide levels (63-80 mg/l), adequate sedation was not achieved. Carbon dioxide sedation at high levels (330-550 mg/l) might be applicable, but further research is needed. However, carbon dioxide sedation at very high levels (400-1400 mg/l) the welfare of the fish seemed to be compromised. Percussion stunning proved to be a good killing (stunning) method based on handling stress assessments. Based on the quality assessments either of the bleeding methods, gill cutting and direct gutting, can be successfully applied for Atlantic cod.
Despite the fact that pre-rigor filleting has several advantages like increased freshness and lower transportation costs, pre-rigor processing also presents problems. As seen in this study fillets cut post rigor were superior to fillets cut pre rigor in terms of various quality properties such as fillet colour, water content, water holding capacity. The shape of pre-rigor processed fillets was different from traditional post-rigor fillets.
In terms of chilling efficiency, live-chilling of cod is as effective as traditional chilling using flake ice after gutting. The results do not indicate better freshness of superchilled cod (gutted or filleted) compared to cod stored in ice after 7 days. However, after 14 days of storage the potential advantages of superchilling of gutted cod became more prominent with lower microbiological activity, better maintenance of freshness compared with traditional ice stored cod.
Assessments of fish welfare are difficult, and the only reliable assessments were ECG and EEG measurements, but these measurements are not applicable in the industry. Fish behaviour and assessments of Vestibulo-ocular reflex (VOR) might be usable, but needs to be used with caution. Obtaining relevant blood parameters and interpretation of these related to both fish welfare and stress at the time of harvest can be complicated. Our results consistently showed that perimortem handling stress did not cause inferior flesh quality, and indicates that farmed cod can be processed with little risk of reducing product quality.
This study has shown that Atlantic cod is not easily excitable, and is more resistant to handling stress than several other fish species. However, this fact should not neglect attention to handling practices since gentle handling is a pre-requisite for adequate fish welfare. Based on the results from this thesis a processing line for farmed Atlantic cod is suggested and presented in the thesis | nb_NO |
