Cortisol can increase the susceptibility of brown trout, Salmo trutta L., to disease without reducing the white blood cell count

Chronic elevation of plasma cortisol levels in the brown trout by means of slow-release, intraperitoneal implants increased the susceptibility of the fish to disease. Elevation from a mean basal level of 1–4 ng/ml to ∼10 ng/ml for a period of 2–4 weeks was sufficient to increase the mortality rate due to furunculosis, Saprolegnia infection and bacterial fin-rot. This level of plasma cortisol is well within that capable of being produced by the fish under conditions of chronic stress. The increase in susceptibility to disease was not accompanied by a reduction in the number of circulating lymphocytes and it is suggested that under certain conditions chronically-elevated cortisol levels may be more sensitive, predictive indicators of reduced disease-resistance than are changes in blood cell counts

Ecological effects and causal synthesis of oil sands activity impacts on river ecosystems: water synthesis review

Abstract: Oil sands development in the lower Athabasca River watershed has raised considerable public and scientific concern regarding perceived effects on environmental health. To address this issue for tributaries and the mainstem of the Athabasca River in the Athabasca Oil Sands Region, the Water Component of the Joint Oil Sands Monitoring (JOSM) plan produced monitoring assessments for seven integrated themes: atmospheric deposition, tributary water quality, river mainstem water quality, groundwater quality and quantity, water quality and quantity modelling, benthic invertebrate condition, and fish health. Our review integrates and synthesizes the large and diverse datasets assembled in the seven JOSM theme assessments to: (a) evaluate possible environmental effects based on known sources and candidate proximal causes, and (b) determine the importance of cause-of-effect pathways related to contaminant, sediment and nutrient inputs. Although JOSM research identified ecological effects that appear to be associated with contaminant exposure, the source of this exposure is confounded by co-location of, and inability to differentiate between, oil sands operations (principally released by atmospheric emission) and inputs from the natural bitumen outcrops (e.g., erosional material transported by surface and groundwater flows). Nutrient enrichment from treated municipal sewage effluent was the dominant ecological effect observed for the mainstem Athabasca River, associated with increased fish size and changes in invertebrate assemblages, likely because this pollution source is discharged directly into the river. The ecological causal assessment method proved to be a useful tool for better understanding how stressor sources relate to ecological effects through candidate proximate causes. Factors that confound our ability to assess the ecological effects of oil sands development focus on our inability to adequately differentiate between contaminants supplied from natural and anthropogenic contaminant sources. Our causal synthesis identifies options for changes in future monitoring to better anticipate and detect degradation in the ecosystem health of the lower Athabasca River and its tributaries.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author