Diluted bitumen (dilbit) is one of the primary exports from the Alberta Oil Sands Region and is transported across much of North America by pipelines and rail. The effects of this petroleum product on freshwater environments are still poorly understood. This thesis addresses the potential effects of a freshwater dilbit spill on small-bodied fish through a combination of lab and limnocorral experiments. The sensitivity of wild fathead minnows (FHM; Pimephales promelas) to residual concentrations of the water accommodated fraction (WAF) of dilbit in order to determine the effects of a spill after applying remedial. FHM were exposed to a treatment of 1:100,000 and 1:1,000,000 WAF to water or 100% pure reference lake water in a laboratory for 21 days followed by a 14-day depuration. A combination of confinement and handling stress resulted in over 50% mortality across all treatments and significantly lower body condition compared to an unconfined reference sample from the source lake. In order to create a less stressful environment for the toxicity testing of wild fish, the following year a large-scale limnocorral study was conducted at IISD-Experimental Lakes Area in northwestern Ontario. Seven 10 m diameter limnocorrals were treated with a regression of dilbit spill volumes resulting in mean daily total petroleum hydrocarbon (TPH) of 169-1646 g/L. Two limnocorrals served as reference systems. Adult finescale dace (FSD; Phoxinus neogaeus) were released in the limnocorrals 21 days after dilbit addition and were exposed for two months. No FSD were recaptured from the three highest dilbit treatments. Despite biliary metabolites indicating increased interaction with the dilbit with increased exposure, there were no significant trends in condition factor, somatic indices, liver cell size or gonadal development with increased mean TPH. The basal epithelial layer on the secondary lamellae of the gills was thinner in fish from limnocorrals compared to the lake indicating the continued potential for confinement stress. The results of both studies emphasize the importance of assessing the effects of multiple stressors in the context of dilbit spills.