Cognitive bias as an indicator of emotional state and welfare in captive zebrafish
AuthorTan, Sern Loong Timothy
AffiliationSchool of BioSciences
Document TypePhD thesis
Access StatusOpen Access
© 2017 Dr. Sern Loong Timothy Tan
Concerns regarding animal welfare are ultimately predicated on the assumption that animals can experience subjective feelings, which are the prerequisite to experiencing suffering, pain and pleasure. Assessing the subjective feelings of animals directly, however, is difficult and perhaps impossible due to their personal nature. Existing approaches in animal welfare research primarily focus on the physiological and behavioural components of emotional (affective) states of animals, as indices of the subjective feelings of animals, however these have several limitations. For example, many of these measures do not give information about emotional valence (whether an emotion is positive or negative), but rather emotional intensity, and in many cases confounding explanations make it difficult to interpret the data unambiguously. Recently, new methods of assessing animal welfare, based on the cognitive aspects of emotional states, have provided ways of overcoming the disadvantages of existing techniques. In humans, it is well known that cognition and emotion are closely linked and reciprocally related. By assessing the cognitive aspects of individuals, such as decision-making, attention and memory, we can gain valuable insight into their emotional state. These phenomena, known as cognitive biases, are increasingly being explored in mammals and birds, but no systematic research has yet been conducted on fish. Since very large numbers of fish are used in scientific research, as well as the commercial pet trade and fisheries industry, an understanding of their cognition can provide useful information for addressing welfare issues for this animal group. In this thesis, I investigated three forms of cognitive bias – judgment bias, attention bias, and sensitivity to reward shifts – using zebrafish (Danio rerio) as a model species. I aimed to determine if these cognitive biases can be detected in zebrafish, and if so, whether tests can be designed to make use of these cognitive biases to inform zebrafish welfare. Designing appropriate experimental set ups, while taking into account the cognitive abilities of zebrafish proved to be challenging. Judgment bias tasks generally require extensive pre-conditioning, and I was unable to condition fish to an appropriate level for subsequent judgment bias testing. Future experiments would have to refine the conditioning process to improve conditioning success. Attention bias, however, required no pre-conditioning, and I found that zebrafish to which I had applied a stressor would position themselves further away from a potentially threatening stimulus. I believe that this approach could potentially be used as a basis for assessing affective states in fish. In the sensitivity to reward shift task, I found evidence that the nature of conditioning to the task was mediated by habitual behaviour rather than goal-directed behaviour, thus affect did not seem to play a major role during that process. The empirical studies described in this thesis were, for the most part, preliminary attempts at investigating cognitive bias in a previously unstudied taxonomic group. I recommend that considerable further work be conducted on understudied taxa, especially for those where large numbers of individuals are subjected to experimental research that has the potential to negatively impact their welfare. I am optimistic that cognitive biases could eventually become a routine aspect of welfare monitoring for a range of species in a variety of animal husbandry settings, given the opportunity of funding and further research.
Keywordscognitive bias; emotion; affective state; animal welfare; judgment bias; attention bias; sensitivity to reward shifts; zebrafish; fish
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