Environmental stress shapes the neurobiology and behavior of fish

Understanding the interaction between the environment and the brain and behavior is fundamental for the management of captive fish as well as for the conservation of wild populations. Anthropogenic disturbance and natural stressors in the environment influence how fish behave on a daily basis. Changes in the brain can help fish adjust their behavior and so cope with stressors in the environment. The way that fish respond to stressors, however, is a dynamic process and there are multiple mechanisms that can lead to changes in physiology, neuromodulation and behavior. Therefore, a more comprehensive understanding of how different environmental stressors affect fish is needed if we are to make informed management decisions for both captive and wild populations.;The research described in this dissertation has used a comparative approach to investigate various types of stressors and how they affect the relationship between brain and behavior in different species of fish. The first study explored the effects of a natural stressor, predation pressure, on the learning ability of the Panamanian bishop (Brachyrhaphis episcopi). Cognitive ability of Panamanian bishops on a maze task has previously been shown to vary with respect to predation pressure; fish exposed to low predation were faster and more accurate at learning the location of a foraging patch than fish exposed to high predation. The areas of the brain involved in spatial learning and processing emotions such as fear are located in the telencephalon (the forebrain) of teleost fish. Thus a link between spatial learning and emotion, such as fear of predators, could be expected. Associative learning where much simpler relationships are acquired through conditioning, however, occurs in the cerebellum (the hindbrain) and thus may not be under the same influences that affect spatial learning. Temperament, on the other hand, is known to influence general aspects of learning ability, such that some individuals learn faster and retain information for longer than others regardless of their experience. Thus, the effect of temperament on conditioning ability of the Panamanian bishop was also investigated.;The second study extended the research to a more applied setting and investigated the effects of environmental stress on a common aquaculture species, Atlantic salmon (Salmo salar). Acid rain is caused by the mixing of harmful gases that have been released from industry with moisture in the air but when this acidified water percolates through the soil it can lead to the release of aluminum (Al) into aquatic habitats. Al toxicity has negative effects on the physiology of Atlantic salmon; the metal interferes with the normal osmoregulatory function of the gills. However, the effects of acidic water and Al toxicity on the neurobiology and behavior of Atlantic salmon have been less well studied.;The final project investigated the effects of handling and housing conditions on the development of behavior and neural plasticity on a common laboratory species, the zebrafish (Danio rerio). The use of enrichment in captive environments is known to increase animal sensory and motor stimulation and also promotes the development of behavioral flexibility and neurogenesis. Information about the effect of housing conditions on brain development in laboratory fish is valuable for helping to improve husbandry procedures, but could also inform us about the cognitive capacities of fish reared in captivity. Thus, the effects of enrichment and mild repeated stress were investigated to determine whether these influenced the development of anxiety behavior, learning ability and the relative size of the telencephalon in zebrafish.;Bringing together all three biological systems, it can be seen that the physiological responses to stress that lead to changes in the brain and behavior are complex, and are dependent on a number of factors such as the type and magnitude of stress as well as the life history of the particular species involved. The comparative approach allows us to bridge the gap between brain and behavior research in fish, but the work presented here needs to be extended to other fish species and applied to other biological systems. In this way, we will be able to see how different stressors impact wild and captive fish species under a suite of different conditions, which will help towards implementing better management strategies for these fish in the future. (Abstract shortened by UMI.).