Using physiology and behaviour to assess enrichment strategies for the welfare of rainbow trout

There is an increasing scientific acceptance that fish may feel some sort of fear, pain and distress, which in turn feeds a growing concern for their welfare. Humans impact the wellbeing of a large number of fish in various ways, one of them being through research. Welfare legislation in the UK demand welfare considerations for all animals used in scientific procedures. Furthermore, welfare and enrichment needs for fish are included in the Appendix A of the European Convention for the Protection of Vertebrate Animals used for Experimental and Scientific Purposes. As fish are extensively used in research, changing their housing and husbandry to improve welfare is of importance, since fish kept in laboratories are most likely subjected to impoverished environments. Although enrichment programs have been shown to improve health and welfare in various animal species, little is known of their potential for application to juvenile rainbow trout. How best to improve barren experimental tanks for female juvenile rainbow trout used in regulatory research was the broad aim of this PhD. In this thesis, three enrichment strategies for rainbow trout have been examined, using physiological and behavioural welfare indicators. The first study assessed the effects of semitransparent shelters on trout welfare, and a clear message became evident; that shelters of this design should not be considered enrichment for rainbow trout as they had several significant negative impacts, indicating chronic stress in fish from shelter tanks relative to fish in a barren environment. The second study investigated impacts of reduced visual access to conspecifics in the same tank. Habitats with low visual contact between individuals have been suggested to reduce aggression for a range of species, and I have shown that visual barriers appeared to be beneficial to trout as well. The final experiment evaluated effects of high and low water currents on the wellbeing of rainbow trout, and results indicated increased fish welfare when water currents were supplied.Great Western Research, AstraZenec