Lack of knowledge does not justify a lack of action: the case for animal welfare in farmed fish

Nowadays, 50 % of the world’s fish for consumption already originate from aquaculture farms. Predictions indicate that this number will increase to approximately 65 % (Monaco and Prouzet, 2015), which is equivalent to 90 to 100 million metric tons per year by 2030 (World Bank, 2013). Rising production levels are often associated with increased intensification and larger environmental footprints, putting aquaculture at the centre of public debates regarding sustainability and animal welfare. Welfare debates about fish are often focused around one specifi c question: Whether fish are capable of suffering or experiencing pain, and if so, to what extent. This question addresses the cognitive and mental capacities of fish, which are currently topics of intensive scientific debates (Key, 2016; Browman et al., 2019). Hence, the number of studies and peer-reviewed publications about animal welfare specifi cally related to aquaculture-reared species has increased significantly over the last decade, indicating the political and public awareness of the topic (Huntingford et al., 2012). However, the scientific study of welfare in farmed fish is still at an early stage compared to that of terrestrial livestock (Huntingford et al., 2006). It should be noted, that the group of organisms named ‘fish’ is often treated as a group of animals from the same species. ‘Fish’, however, comprise organisms from various taxonomic groups and a large number of species, which account for around 60 % of all vertebrate species (Nelson et al., 2016). They inhabit all aquatic ecosystems and each species has developed particular adaptations to living in their particular habitat. Therefore, anatomical structures, physiological traits and behavioral patterns vary greatly between different fish species according to their taxonomic group, and as a perfect adaptation to the conditions of a particular habitat. This enormous diversity has to be regarded when drawing conclusions about ‘fish’ and each respective species grown in aquaculture. Whether or not pain perception in fish should remain unproven, and even if it proves to be unexperienceable in fish, there is sufficient assignable evidence to justify the same level of animal welfare in farmed fish as in terrestrial livestock. Recent studies have been able to demonstrate that some fish are capable of solving problems (Balcombe, 2016), using tools (Bernardi, 2012) and learning and deploying avoidance behaviour (Yue et al., 2004; Dunlop and Laming, 2006). Certain specimens have even passed self-awareness tests (Kohda et al., 2019). Fish show physiological and behavior al stress responses that are in some way similar to those in mammals. Accordingly, the European general public expects animal welfare to be generally safeguarded during the rearing and slaughtering of fish. This article aims to provide an overview by summarising the prevailing scientific opinion from the field of welfare research in aquaculture within the framework of this issue. Received: September 19, 2019 Revised: November 4, 2019 Accepted: November 26, 2019