Identification of potential welfare indicators for commercially farmed King salmon (Hāmana, Oncorhynchus tshawytscha) : a scoping review to inform the development of a national code of welfare : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physiology at Massey University, Manawatu, New Zealand

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Aquaculture – the cultivation of marine plants and animals – is one of New Zealand’s fastest growing primary industries. A major contributor to the growth of New Zealand’s aquaculture industry is the farming of King salmon (Oncorhynchus tshawytscha). Parallel to the growth of the aquaculture industry is an increasing interest in the welfare of farmed fish from people in the industry, government, and public. Under the Animal Welfare Act 1999, fish are considered sentient beings capable of experiencing positive and negative emotions. However, unlike other animals under the Act, fish do not have a Code of Welfare to formally guide farmers to meet their obligations as animal carers under the Act. In order to develop a Code of Welfare for farmed fish, there needs to be an understanding of current and future state of the New Zealand salmon farming industry along with an evaluation of potential areas within production systems that may influence fish welfare, and identification of potential indicators of farmed salmon welfare. The New Zealand salmon farming industry use freshwater and marine-based operations to farm King salmon. Juvenile salmon are reared in freshwater hatcheries until they have reached an acceptable weight and/or stage of smoltification before being transferred into grow-out cages. Smolt are grown out in net cages, situated within either freshwater hydro-canals or coastal bays of the South Island, until they reach a harvest weight of ~4kg. At harvest, farmed salmon are stunned and slaughtered using methods such as Aqui-S and carbon dioxide immersion, manual and automatic percussion, and electrical stunning. Brain spiking is also used to euthanise broodstock prior to stripping. The Five Domains Model was used as a guide to evaluate areas of potential welfare impacts within New Zealand salmon farming systems. In terms of nutritional impacts (Domain 1), management of feed withdrawal regimes and factors associated with underfeeding may negatively impact salmon welfare. Appropriate water quality parameters are crucial for the maintenance of adequate environmental living conditions (Domain 2). Water quality parameters that may influence salmon welfare include water flow rate, temperature, oxygen saturation, carbon dioxide concentration, ammonia concentration, and salinity. Impacts on salmon health (Domain 3) may arise from the contraction of infectious bacterial diseases, physical injuries, and the development of spinal deformities. Lastly, in Domain 4, salmon welfare may be impacted through interactions with humans (e.g., handling stress during handling events), other non-human animals (e.g., aggressive interaction with conspecifics or presence of predators), and the environment (e.g., limited ability to exercise agency within barren and confined environments). A scoping review of globally published literature relevant to measures of salmon welfare was conducted to identify potential indicators of farmed salmon welfare. The scoping review identified a total of 112 potential animal- and resource-based indicators of farmed salmon welfare from 60 articles. There was a clear focus on the use of survival-critical indicators reflecting welfare impacts in Domains 1-3 (nutrition, health, and physical environment). A limited number of situation-related indicators (Domain 4) were identified. Of the identified indicators, a large proportion were classified as animal-based indicators sampled post-mortem. These indicators can only provide evidence of a previous experience in the animal assessed. To create a reliable and holistic assessment of farmed salmon welfare, contextual information is required for appropriate application and interpretation of welfare indicators with regards to affective experiences and a range of indicators across Domains 1-4 should be used in combination to capture all possible welfare impacts. The 112 unique welfare indicators identified and the understanding of their collective value to the welfare of commercially farmed salmon in New Zealand presented in this review provides industry, government, and policy makers the necessary information to develop regulations and on-farm welfare assessments.
Figures 1, 3, 5 & 6 are re-used with the publishers' permission.