Patterns in Stress and Mortality in Small Ornamental Aquarium Fish and Interventions for Improving Health and Well-being
Date: 4 March 2019
Thesis or dissertation
University of Exeter
PhD in Biological Sciences
The ornamental fish trade is an industry of significant size and scope, trading over 1.5 billion fishes each year, and worth approximately over 370 million USD. Ornamental fishes are kept world-wide, and are one of the most popular pets in UK households. The industry is currently experiencing steady growth, and has done since the FAO ...
The ornamental fish trade is an industry of significant size and scope, trading over 1.5 billion fishes each year, and worth approximately over 370 million USD. Ornamental fishes are kept world-wide, and are one of the most popular pets in UK households. The industry is currently experiencing steady growth, and has done since the FAO began keeping records in the 1970s. Despite this, the welfare of fishes within the industry remains one of the least-studied areas in the field of animal welfare. Mortality rates of fishes within the industry are debated, with estimates ranging from less than 2% to over 70%; however, a lack of clear data means that the accuracy of these figures is difficult to determine. Where mortality is believed to be high, stressors in the supply chain are thought to be a significant contributing factor. In this thesis, I explored some possible interventions designed to reduce the stress experienced by ornamental fishes. Stress in fishes can be measured in a variety of ways, but the most common way is probably measurement of cortisol release rates. However, cortisol has often previously been measured in fishes by taking a blood sample – a technique which cannot be applied to many ornamental species as they are too small to obtain enough blood. Instead, cortisol released by small fishes can be measured in the fish holding water. I carried out a study to validate the use of this method in my study species and found that cortisol can be detected in the holding water of all three species, although I did not find clear differences between stressed fishes and controls. This highlighted the importance of using a variety of measures of stress, including behavioural measures, which are one of the most cost-effective ways to assess stress, and can easily be implemented in the ornamental fish supply chain. Based on the literature, personal observations of industry practices, and the results of my analyses, a number of interventions intended to help reduce stress in ornamental species were developed. These involved training handlers to catch fish more effectively, providing neon tetras with environmental choices to allow them to select conditions which might promote welfare, and conditioning guppies to associate handling events with a reward or a predictable signal. I found fish which were not handled but were exposed to trained handlers showed fewer behavioural signs of stress than those exposed to untrained handlers, and that neon tetras showed preferences for particular tank backgrounds over others. However, I did not find any evidence that trained handlers caused less stress in handled fish, or that conditioning led to lower stress in handled fish. The results of this project suggest that there are a number of sources of stress and poor welfare in the ornamental fish industry which may be contributing to high mortality rates. However, many of these sources can be addressed, either through application of current best-practice guidelines or by introduction of training programmes which encourage understanding and empathy for fishes. Further work aimed at developing interventions including enrichment strategies, conditioning regimes, and other areas of research, will likely help to further reduce stress and mortality, and improve fish welfare.
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