Abstract
The welfare of fish has become an explicit goal in legislation regarding fish farming and slaughter. One of the demands is that farmed fish shall be unconscious when bled. Some stunning methods are explicitly banned, among them carbon dioxide (CO2). However, this has been by the far most common method in Norway. In order to give the industry time to adapt, the ban has yet to be put into force. On behalf of the Norwegian fish farmers’ organisation (FHL) we have evaluated the alternative methods electricity and percussive stunning and their challenges and advantages under practical slaughter. Results from evaluations as well as research projects will be presented.
Some important welfare challenges at slaughter are independent of stunning method. These include crowding of fish, pumping, poor water quality, and time kept out of water. These factors cause stress resulting in the depletion of energy reserves, and even physical injury. High fish flow rates may reduce the performance of the stunning equipment.
A method for electrical stunning of fish submersed in seawater failed to satisfy the legal claim of immediate unconsciousness. To avoid spine fractures and blood spots in the fillet, which may be a problem with electric stunning, this system made use of a pre-stun treatment with low voltage electrical stimulation, under which the fish were not rendered unconscious. Dry electric stunning, i.e. stunning out of water, has undergone a development with increasing voltage and improved stunning quality. A new device has been developed which orientates the fish head first into the stunner. This resolves one important concern addressed by EFSA. Also, the frequency of fillet quality problems has been reduced. However, there is lack of knowledge of risk factors for spine fractures and haemorrhages.
There are two producers of percussive stunning equipment on the Norwegian market. Both stunners function well when used according to the producers’ instructions. A correct stun causes irreversible unconsciousness or death. Variation in fish size is the main challenge. Also this equipment has steadily improved.
The described alternative methods have been under continuous development the last years and from a fish welfare point of view they are far better methods than CO2, which is highly aversive to fish. When CO2 is used at low concentrations in combination with live chilling, the fish are sedated but not anaesthetized. Nitrogen gas does not seem to be suitable. There are promising preliminary tests on CO, a gas which does not seem to cause aversive reactions in salmon.
Some important welfare challenges at slaughter are independent of stunning method. These include crowding of fish, pumping, poor water quality, and time kept out of water. These factors cause stress resulting in the depletion of energy reserves, and even physical injury. High fish flow rates may reduce the performance of the stunning equipment.
A method for electrical stunning of fish submersed in seawater failed to satisfy the legal claim of immediate unconsciousness. To avoid spine fractures and blood spots in the fillet, which may be a problem with electric stunning, this system made use of a pre-stun treatment with low voltage electrical stimulation, under which the fish were not rendered unconscious. Dry electric stunning, i.e. stunning out of water, has undergone a development with increasing voltage and improved stunning quality. A new device has been developed which orientates the fish head first into the stunner. This resolves one important concern addressed by EFSA. Also, the frequency of fillet quality problems has been reduced. However, there is lack of knowledge of risk factors for spine fractures and haemorrhages.
There are two producers of percussive stunning equipment on the Norwegian market. Both stunners function well when used according to the producers’ instructions. A correct stun causes irreversible unconsciousness or death. Variation in fish size is the main challenge. Also this equipment has steadily improved.
The described alternative methods have been under continuous development the last years and from a fish welfare point of view they are far better methods than CO2, which is highly aversive to fish. When CO2 is used at low concentrations in combination with live chilling, the fish are sedated but not anaesthetized. Nitrogen gas does not seem to be suitable. There are promising preliminary tests on CO, a gas which does not seem to cause aversive reactions in salmon.