The Effects of Environmental Enrichment and Stress in Fish

AbstractThe use of environmental enrichment procedures provide animals in a laboratory setting an opportunity to express behaviors typically seen in the wild. When animals are provided with more natural environment stimuli, stress levels are lower compared with controls not exposed to enriching stimuli. Stress levels of zebrafish, for example, are reliably lower when they are placed in an enriched environment for several days containing a plastic plant, which has anxiolytic effects. Despite several studies demonstrating the enriching, anxiolytic effects of a plastic plant, virtually nothing is currently known about the specific features (shape, color, size…) of a stimulus (plant) that are enriching. The current research seeks to examine whether simply seeing a plant is enriching (i.e. will reduce stress levels of zebrafish) or whether zebrafish need to see the plant and interact with it 3-dimensionally (swimming around it, hiding behind it…).Fish were randomly assigned to 1 of 3 experimental housing environments: barren 10-gallon tank (“barren group”; n=5), an enriched tank with a 3-D green plant (“3-D plant group”; n=5), or an enriched tank containing the same plastic plant (n=5) that is flat against the wall of the aquarium tank (“flat plant” group; n=5). After a period of 3 weeks, the stress levels of individual zebrafish were measured in the light-dark test and the novel-tank test. Although it was found the “flat plant” group displayed a reduced stress response compared with controls, the 3-D plant group displayed the least stress (most enriched).