The Food and Agriculture Organisation (FAO) in 2018 showed that the annual increase in fish consumption outpaced the growth in the consumption of meat from terrestrial animals. Unfortunately, welfare practices for aquatic animals remain incipient when compared to farmed terrestrial vertebrates. Within the aquaculture production chain, pre-slaughter and slaughter procedures are considered an important fish welfare issue, but often lack efficient humane slaughter methods. In summary, a slaughter is considered humane when performed in the absence of pain and fear, from the reception of animals in the slaughterhouse until their death. A humane slaughter process consists of a stunning step followed by the bleeding of an unconscious animal until its death.
The OIE Aquatic Animal Health Code, first adopted in 2012, and most recently updated in 2013, summarises the recommended fish slaughter methods (OIE 2021). _For methods to be considered humane they need to result in the immediate loss of consciousness. Mechanical and electrical stunning, when applied correctly, are humane slaughter methods - both cause the immediate loss of consciousness. But these methods are rarely used. In practice, the most commonly used slaughter methods are not humane: chilling with ice in holding water, carbon dioxide (CO2) in holding water, chilling with ice and CO2 in holding water, salt or ammonia baths, asphyxiation by removal from water and direct exsanguination without stunning, are used in many countries, for many species, mostly tilapia and carp. All these methods have been shown to result in poor fish welfare and should be avoided. Mechanical or electrical stunning should be the preferred options.
In Brazil, for example, Coelho et. al, 2022, studied 62 facilities and observed that live chilling was the most commonly used method (82.0%), followed by electronarcosis (18.0%). In the case of tilapia, exsanguination (38.5%) and decapitation (2.5%) were prevalent. However, most Brazilian facilities (59%) fail to report the killing methods used.
We control what we measure
To be able to recognize the lack of humane slaughter we first we need to assess the stunning efficiency. While absence of consciousness may be difficult to recognise, signs of correct stunning include i) loss of body and respiratory movement (loss in opercular activity); ii) loss of visual evoked response (VER); iii) loss of vestibulo-ocular reflex (VOR, eye rolling) (OIE, 2015).
The practical Welfare Assessment Protocol, published by Pedrazzani et. al in 2020, successfully proposed the integration of individual welfare indicators into a single tilapia welfare assessment protocol, which proved easy to use and adapted to different farming practices. Regarding effective stunning, the indicators for the evaluation of tilapia consciousness included the clinical signs of opercular rate - estimated respiratory rate by counting the opercular movements (OR), vestibulo-ocular reflex, eye rolling (VOR), equilibrium in water, which is assessed by the position of the fish and its ability to swim when placed in the water. (EQ) and the tail-grab-reflex, the technique of grabbing the animal’s tail to check if the fish tries to escape, (TGR). The indicators were classified in a 3-point scoring system as shown in Table 1. During this study, six properties refused to assess their slaughter practices. This suggests that some farms are insecure about the adequacy of their current practices.
Continuity and Actual Change
As part of the FAI Tilapia Welfare Project, funded by The Open Philanthropy, assessments have been performed on several tilapia farms and slaughterhouses in Brazil. The constant application of the protocol during the full production cycle, including slaughtering, has been a powerful tool to support the decision-making process that led to adapted handling procedures and investments in equipment to support effective stunning. To make the implementation of humane slaughter accessible to the industry, an offline tilapia Welfare Assessment App is freely available and in use to facilitate the information collection as well as to provide feedback to the users. As an interesting case study, one of the companies involved in the project has purchased electrical stunning equipment, to improve welfare practices and provide better working condition for their staff. With the right knowledge and methodology, it is possible to promote positive animal welfare changes within the industry. It is relevant to stress the importance of appropriate regulation, but successful private initiatives demonstrate both the feasibility and the need for improvements in fish slaughter practices.
Conclusion
The current scenario highlights the urgent need for development and enforcement of humane fish slaughter techniques, with routine supervision and normative requirements. We understand that with appropriate tools for welfare assessment and effective knowledge-transfer, it is possible to drive constant improvement on tilapia welfare with the agreement and support of fish farmers and the industry.
MEG Coelh, AS Pedrazzani, MH Quintiliano, F Bolfe, CFM Molento 2022 Fish slaughter practices in Brazilian aquaculture and their consequences for animal welfare. Animal Welfare 2022, 31: 187-192 ISSN 0962-7286 doi: 10.7120/09627286.31.2.00
FSA 2018 Guidance on the assessment criteria for applications for new or modified stunning methods regarding animal protection at the time of killing. The EFSA Journal 16: 5343. https://doi.org/10.2903/j.efsa.2018.5343
FAO 2018 The State of World Fisheries and Aquaculture (SOFIA). http://www.fao.org/documents/card/en/c/I9540EN/
Pedrazzani AS, Quintiliano MH, Bolfe F, Sans ECO and Molento CFM 2020 Tilapia on-farm welfare assessment protocol for semi-intensive production systems. Frontiers in Veterinary Science 7: 1-16. https://doi.org/10.3389/fvets.2020.606388
World Organisation for Animal Health (OIE) 2021 Aquatic Animal Health Code. http://www.oie.int/standard-setting/aquatic-code