The Repository @ St. Cloud State

Open Access Knowledge and Scholarship

Date of Award


Culminating Project Type


Degree Name

Biological Sciences - Cell and Molecular: M.S.




College of Science and Engineering

First Advisor

Heiko L. Schoenfuss

Second Advisor

William Cook

Third Advisor

Shiju Zhang

Fourth Advisor

Rong-Lin Wang

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.


Male fathead minnows (Pimephales promelas) establish social hierarchy. The social status of individual fish is determined by the expression of secondary sex characteristics (SSCs) that develop during the reproductive window, and is vital for reproductive success during the spawning season. The social rank of each male is linked to the concentrations of circulating androgens: testosterone and 11-ketotestosterone that influences the expression of SSCs, and is under the control of hypothalamo-pituitary-gonadal (HPG) axis. Since the dominant and subordinate males are initially under different physiological conditions, we proposed that they belong to two significantly different subpopulations. Here we demonstrate that male fish population is indeed heterogeneous. This is in contrary to the previously held assumption that single sex exposure populations are homogeneous.

Our results demonstrate that social hierarchy influences the fish responses to the contaminants of emerging concern (CECs). We anticipate our study to be a starting point for re- evaluation of toxicological data analysis in single sex exposure experiments.


We would like to thank all authors of manuscripts that were used in this study, all undergraduate and graduate students who assisted with these experiments, Dr. Cook for support, SETAC for recognition of the importance of this study, and US Fish & Wildlife Services and National Science Foundation for grants that made these studies possible.



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