College - Author 1

College of Science and Mathematics

Department - Author 1

Biological Sciences Department

Degree Name - Author 1

BS in Biological Sciences



Primary Advisor

Gita Kolluru


The guppy, Poecilia reticulata, is a common study organism for behavioral and other ecological experiments (Houde, 1997). As far as we know, no previous data have been compiled regarding hormones and condition index of guppies. In this experiment we examined the relationship between circulating levels of three hormones (testosterone, 11-ketotestosterone and cortisol) and condition index in males and also made comparisons among the hormone levels, for three guppy sites from the northern range of Trinidad – Aripo River, Marianne River and Small Crayfish River. Hormone samples were obtained using non-invasive water borne techniques and quantified by our collaborator. The condition index of guppies was calculated as the ratio of mass per length3. We predicted the following relationships: positive relationships between testosterone (T) and 11-ketotestosterone (11KT), condition index (CI) and 11KT, and CI and T; negative relationships between 11KT and cortisol (C), T and C, and CI and C. We found: a positive relationship between 11KT and C, 11KT and T, and C and T for the Small Crayfish River population. Aripo River and Marianne River populations displayed no significant relationship between 11KT and C, and 11KT and T. The Aripo River population showed a significant positive relationship between C and T, but the Marianne River did not show a significant relationship. Overall, there were no relationships between any of the hormones and CI for any site. Our findings indicate that there may be genetic differences among the populations indicated by the hormone differences. Further experimentation is necessary for more comprehensive understanding of the functions of these hormones in the guppies.