Animal movement has had a long history of study in the fields of behavioural ecology and toxicology, but rarely is the ecological context of behaviour in toxicology directly addressed. To explore how movement might be influenced by both sex differences and habitat contamination, I conducted studies on the round goby, an invasive fish, in a highly polluted part of Lake Ontario. In the first half of my dissertation I examined the reproductive biology of this species, finding evidence of multiple male reproductive tactics, and extended this to predict sex differences in goby movement. I showed that male fish were more exploratory in the laboratory, and over multiple years moved further in the field than females. This difference may predict variation in sex ratio along a round goby invasion front. Second, I accumulated multiple lines of evidence for contaminant exposure in these fish, validating their utility as a contaminant sentinel species in the field. With the same battery of behavioural tests, I revealed that round goby collected from cleaner sites were more exploratory than fish from highly contaminated sites in the laboratory, but moved similar distances in the field. Although changes in activity level are the most frequently used behavioural measure of contaminant exposure, the ecological relevance of change was not apparent in this study. These results challenge the utility of movement as an integrated biomarker of contaminant exposure beyond the laboratory.