THE EFFECTS OF POPULATION DENSITY AND ENVIRONMENTAL COMPLEXITY ON AGGRESSIVE BEHAVIOR OF ZEBRAFISH

Environmental complexity has been  demonstrated to improve laboratory rodent wellbeing and enhance research data.  Relatively little is known with regards to the type of environmental complexity that might be useful for zebrafish (Danio rerio ).  It has been well documented that suboptimal environmental conditions can subject fish to chronic stress and distress, cause abnormal behavior, and add  additional research variables. The lack of enrichment contributes to zebrafish aggression and the formation of dominance hierarchies. Dominant fish differ significantly from fish subjected to subordination through greater access to food, shelter and mates; immune functions; metabolism; susceptibility to toxins, reproduction, and stress. See table below.    Such dramatic differences may easily lead to confounding research outcomes due to the unfavorable impact observed on fish welfare.  Therefore, this study aims to  explore a model to evaluate the impact of environmental enrichment/complexity on aggression, a behavior that can be measured and to develop an environmental enrichment structure that can increase complexity of the environment, and be easily cleaned, stored, and incorporated into large facility husbandry practices as the figures below outline.   

Preliminary findings indicate enrichment appeared to have decreased aggression, but further trials are required to prove significance.  Furthermore, the study demonstrated that zebrafish reared in an enrichment free enviro nment preferred  the environmental enrichment structure, which was also influenced by dominance status within the groups of 2 to 4 fish.   Further trials are currently being conducted to acclimatize the fish to the enrichment structure and provide a longer testing intervals to help develop statistical significances for the study.