Aquaculture North America

Humane slaughter of salmonids easier said than done

April 26, 2023
By Mykolas Kamaitis

Photo: © Mikko Palonkorpi / Adobe Stock

The goal of most salmonid aquaculture operations is to produce nutritious food for human consumption. A great deal of focus is placed on breeding and genetics, early rearing, nutrition, environmental optimization, maximizing productivity and minimizing stress throughout the lives of your fish, and many producers appreciate that the same level of care needs to be placed on harvest and processing. 

Many fish farmers have adopted and implemented slaughter processes which are considered humane, which is important on number of levels, including consumer confidence, public acceptance, product quality, and ethical farming practices. Canada’s first Code of Practice for farmed salmonids has been developed (initiated by the National Farm Animal Care Council and Canada’s aquaculture sector) and as part of its development, a list of salmonid welfare issues was identified.

A topic of focus was fish welfare, particularly as it pertains to certain slaughter practices. The Code of Practice will require all Canadian salmonid aquaculture operations to adhere to slaughter standards and practices considered humane by 2025. 

For those producers who already use accepted slaughter practices, this new requirement may seem past-due when it comes to running an aquaculture operation. In principle it is important to constantly evolve and improve our practices, particularly when it comes to animal welfare. For a number of producers however, this change is not as simple as just purchasing off-the-shelf technology to fill this need in their operation. Before exploring that point further, let’s discuss fish slaughter, and what is considered humane (and inhumane).


The term ‘slaughter’ generally refers to the process of killing animals intended for human consumption.  For fish, this specific process will vary depending on the size and species of fish, as well as the overall production-flow and setup of an operation. 

Humane slaughter is a two-step process: first an animal must be stunned or rendered unconscious so that they cannot perceive pain, followed by the second step of killing the animal, with one of several techniques. 

Typical acceptable methods for the stunning step of humane slaughter include the use of manual blunt force trauma, captive bolt/percussive stunner (non-penetrating or penetrating), electrocution, pithing, and cervical dislocation/decapitation, among some others. Each of these methods has advantages and shortcomings, and what works best for one operation may not be appropriate or manageable for another. 

The killing step of humane slaughter is usually exsanguination (bleeding-out) or rapid chilling. Exsanguination is recognized as the best practice as a killing step and has the benefit of improving product quality (e.g. less blood-spots, decreased blood odour/off-flavour, etc.). 

The Ontario Animal Health Network (OAHN) has put together some great information on humane slaughter, including explanations and comparisons of different slaughter methods, particularly for smaller-scaled producers; this includes a case study evaluating a low-cost, on-farm humane slaughter method.

Many freshwater fish producers use ice slurry baths, or rapid chilling, as the sole step of slaughter. This process involves netting or pumping fish into an ice water bath, relying on the temperature differential between the bath and their ambient environment to induce hypothermic shock of the fish. 

The issue with using this method for salmonids is that they can tolerate low temperatures; furthermore, when fish are slaughtered during colder ambient temperatures, the differential between the ice slurry/bath and ambient can be very minor to negligible. Although this method may be appropriate for relatively small-sized warmwater fishes, it is not considered humane as a sole step of slaughter for a temperate-, cool-, and cold-water fishes that can tolerate water temperatures of 4 C or colder. Rapid chilling is also not an appropriate sole step when slaughtering medium to large sized fish because their surface area to volume ratio does not allow for rapid enough chilling (AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition). 

Dr. Marcia Chiasson MSc, PhD, is the Manager of the Ontario Aquaculture Research Centre and has been a lead on the OAHN humane slaughter work previously mentioned. She has worked closely with Ontario fish farmers regarding the adoption of humane slaughter practices. Discussing this transition with Dr. Chiasson, there are significant cost barriers towards the implementation of these practices, especially for mid-sized producers.  

For these producers, there seems to be a lack of financially viable options for humane slaughter equipment at their scale of production, which is something that will need to be addressed if we are to be successful in implementing these new Canadian salmonid slaughter requirements. Another significant challenge in the implementation of these requirements, is the central Canadian climate. Sub-zero temperatures, which many Canadian fish producers face for 4-6+ months of the year, pose several major barriers to the use of harvest equipment. 

The logistics of adapting harvest equipment set-ups to function both during hot summer months and when the water is ice-covered poses significant challenges. Furthermore, many equipment options, such as percussive stunners, won’t function properly at such cold temperatures. 

Just as humane slaughter involves more than one step, the implementation of these new slaughter requirements will require multiple phases to be adopted. The farmed salmonid Code of Practice was a valuable first step in identifying gaps and areas of improvement when it comes to salmonid welfare, not least of which is slaughter practices. There needs to a collaborative approach between industry and regulators to enable producers to implement these practices on farm. The realities of freshwater fish farming in the Canadian climate also needs to be acknowledged and considered when setting timelines for the implementation of these requirements. 

Lastly, those regulators who implement these sorts of requirements, should also bear part of the responsibility of helping farmers access the necessary technology needed for this shift in practice. Most farmers will agree that they want to raise their animals ethically and give their livestock a good life from egg until harvest, but we need to see viable options which can be logistically achieved in our climate and to do so without placing an unreasonable financial burden on producers. 

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