Document Type


Degree Name

Master of Science (MSc)



Program Name/Specialization

Integrative Biology


Faculty of Science

First Advisor

Deborah MacLatchy

Advisor Role

Thesis Supervisor

Second Advisor

Lucy Lee

Advisor Role

Thesis Co-supervisor

Third Advisor

Andrea Lister

Advisor Role

Research Coordinator


Endocrine disrupting substances (EDSs) comprise a wide variety of chemicals that perturb normal endocrine function including developmental and reproductive processes in vertebrates. The synthetic estrogen 17α-ethynylestradiol (EE2) is a commonly-used model EDS because of its environmental relevance and its effects on the reproductive endocrine system. Early life-stage exposure of fish to estrogenic EDSs causes effects such as intersex (ovotestes in males) and feminization. This study aims to confirm the period of gonadal differentiation in the estuarine killifish or mummichog (Fundulus heteroclitus) and to determine the sensitivity of gonadal development to EE2. Artificially-regressed mummichog were spawned, and fertilized eggs were collected and exposed to EE2 (0, 10, 50 and 250ng/L) within 8 h of spawning. Embryos and larvae were continually exposed in petri dishes and beakers (26˚C) and sampled weekly from hatch date to 10 weeks post-hatch (wph) to determine histologically the sensitivity of gonadal development to EE2. Exposure to EE2 (10-250ng/L) resulted in a concentration-dependent increase in skeletal abnormalities and mortalities; larval lengths proved insensitive to EE2 exposure. Complete gonadal differentiation in mummichog occurred by 3 wph in control groups, whereas exposure to EE2 accelerated gonadal differentiation as early ast 1 wph in all EE2 exposed groups. Sex ratios were skewed (>80% female phenotype) within all groups treated with EE2. This study demonstrates that early onset of exposure elicits effects on developing mummichog as exposure of EE2 prior to establishment of endogenous differentiation pathways influenced and altered sex differentiation, resulting in feminized groups of fish at environmentally-relevant and higher concentrations.

Convocation Year


Convocation Season