By Arezo Mansoor and Caroline Kim

Faculty Mentor: Dianne Baker

Abstract

Effects of isolation and co-housing on cortisol levels and anxiety- like behavior in female zebrafish

Authors: Arezo Mansoor, and Caroline Kim

Abstract
Cortisol, a glucocorticoid hormone, is synthesized from cholesterol and released through the hypothalamic pituitary interrenal (HPI) axis, which is functionally analogous to hypothalamic pituitary adrenal (HPA) axis in mammals. In zebrafish, cortisol concentration is commonly used to assess stress levels. The objective of this study was to test the effects of housing condition on female zebrafish stress levels and stress behavior. We hypothesized that co-housing increases stress and anxiety-like behavior compared to individual housing. A total of 84 adult female zebrafish (Danio rerio) were assigned to one of three housing conditions for one week prior to the experiment: individually housed females, grouped females and grouped mixed-sex fish. After acclimation, zebrafish were assigned to control, stress, and behavior treatments. Anxiety-like behavior was assessed using a 2-minute Novel Tank Diving Test (NTDT), measuring bottom dwelling time, number of trips to the top, and latency to reach the upper region of the tanks. Whole body cortisol concentrations were measured in replicate fish (n=3) from each housing condition, at rest and after an acute stressor, using a commercial ELISA. A two-way ANOVA revealed no significant difference between housing condition (individual, grouped and co-housed) and treatment (control vs stress) on cortisol levels (F (2,17) = 2.80, p = 0.089) and no significant difference between the treatments (F (1,17) = 4.35, p = 0.052). Additionally, there was no significant interaction between the housing condition and treatments (F (2,17) = 0.57, p = 0.579). Behavioral results showed a trend in which grouped female zebrafish exhibited higher exploratory activity, while individually housed and co-housed females showed lower activity and higher bottom dwelling time; however, these differences were not statistically significant.