Zebrafish are often used in studies involving social behavior because they readily form shoals. A shoal is any group of fish congregating together for social reasons. Zebrafish form shoals because of the many benefits these social groups provide such as defense against predators and improved foraging success. Because the zebrafish is an animal that exists in a large social grouping, it provides an interesting perspective on understanding the influences of stress on social behavior. Using zebrafish as a model, this thesis aims to determine how specific social situations are affected by and affect stress and associated cortisol levels. In order to determine how stress and cortisol levels are affected by social situations, the hormones released by a focal zebrafish in the presence of differently sized shoals of stimulus zebrafish were collected and measured. Due to the shoaling behavior of zebrafish and the research from previous studies suggesting that zebrafish prefer large shoals, it was predicted that cortisol levels will be lower when fish are associating with large shoals and highest when fish are alone. It was also predicted that a sex difference will be seen, with females expressing lower levels of cortisol than males. Preliminary results displayed that the social situation may have an effect on cortisol expression, with overall levels of cortisol expressed being higher when both males and females were alone (0 fish) compared to when they were exposed to a shoal of 6 fish of the same sex. I hypothesized that increased vulnerability associated with being alone may cause the zebrafish to exhibit higher stress levels, as measured by the expression of cortisol. Contrary to predictions based on previous studies, the preliminary data displayed that females expressed higher levels of cortisol than males overall. This could suggest that without the requirement of asserting dominance in order to mate, the male zebrafish does not express high levels of cortisol.


Social behavior, Zebrafish, Stress, Hormone, Cortisol

Document Type


Year of Completion



Dr. Jennifer L. Snekser

Academic Department