By Arlie Scott, Daniel Johnson

Faculty Mentor: Dr. Dianne Baker

Abstract

Zebrafish (Danio rerio) are traditionally housed in mixed-sex shoals (MSS) in laboratory settings to mirror their natural social environment, a practice which is believed to be the most optimal housing method for the species. To test the impact of housing arrangements on anxiety-related behavior and levels of the stress hormone cortisol, adult male fish were housed in sex-segregated groups of twelve (GM) individual tanks (IM), and mixed-sex shoals prior to testing. To determine the impacts of housing on basal stress and the response to an acute stressor, replicate GM and IM fish were sampled before and after a one-minute net test in which the fish are chased in their tanks for one minute. Following euthanization zebrafish were homogenized, and cortisol concentrations were measured using a commercial ELISA. The results showed that cortisol levels varied across housing conditions, with GM males showing higher mean values (0.093 ± 0.171 ng/mg) and IM males lower values (0.046 ± 0.043 ng/mg). In the stress test, IM males showed an increase of 0.034 ng/mg from the control, while GM males increased by 0.006 ng/mg and MSS decreased by 0.029 ng/mg. However, differences between stressed and control groups were found not to be statistically significant by a Wilcoxon rank-sum test (p=0.968). To test for effects of housing on anxiety-related behavior, replicates IM and GM were subjected to a two-minute Novel Tank Diving Test. Time at bottom of tank, latency to upper zone, and total trips to upper zone were recorded. Results showed that GM males had a lower mean latency time (104.04 seconds ± 8.34) than IM males (109.46 s ±11.5) and MSS males (116.25 s ±5.23). MSS males (113.37 s ±3.37) exhibited slightly less bottom dwelling behavior than GM (117.50 s ±1.30) and IM males (116.25 s ±3.75). GM and MSS males averaged similar numbers of trips to the upper zone (1.17s ± 0.625 and 1.17s ±0.683, respectively), while IM males averaged 0.25 trips. However, these results were not statistically significant across housing conditions for latency to upper zone (Kruskal-Wallis test, p = 0.961), bottom dwelling time (p = 0.190) or number of trips to the top (p = 0.891). With this result this shows that there is no statistical significance in the amount of cortisol and anxiety behavior in in group house versus individual housing and sex segregation.