Comparative toxicity of two diluted bitumens to developing yellow perch (Perca flavescens).

Increasing demand for diluted bitumen (dilbit) has led to the development of the oil sands industry and the expansion of transcontinental pipelines. Dilbit is an unresolved complex mixture with variable diluent and bitumen composition. Thus, it is important to understand the effects of the two most transported dilbits in Canada, Access Western Blend (AWB) and Cold Lake Blend (CLB) on a North America native and freshwater fish species, the yellow perch (Perca flavescens). Fertilized embryos were exposed to both dilbits for 16 days, from <24 h post-fertilization until hatch. The treatment regime was a static daily renewal of water accommodated fractions (WAF) and chemically-enhanced water accommodated fractions (CEWAF) at concentrations ranging from 0.01 to 21.3 µg/L of total polycyclic aromatic compounds (TPACs). Hatched embryos were assessed for malformations and changes in the expression of genes associated with phase I and II detoxification and oxidative stress. The prevalence of developmental malformations increased significantly at the highest concentrations of all treatments, with WAF treatments yielding a higher prevalence than CEWAF. The EC50s for AWB and CLB WAF and CEWAF solutions ranged from 9.8 to 24 µg/L TPACs, with the CEWAF of AWB being the least toxic. Relative mRNA levels of cyp1a showed induction by up to 18-fold in WAF and 50-fold in CEWAF treatments at similar concentrations of measured dilbit in solution. Complementary DNA methylation analysis was assessed and fish embryos exposed to AWB CEWAF and CLB WAF showed decreased DNA methylation profiles with increasing exposure to dilbit, suggesting that global gene expression is increasing in these treatments. With recent approvals of pipelines in North America, these data will support site-specific risk assessments and monitoring of Canadian ecosystems should a pipeline spill occur.

Trait canalization analysis of water quality, temperature, and developmental associations with early life stages of two fish species.

Evaluation of trait robustness based on environmental fluctuation in ontogenetic life stages are needed to evaluate stability and trait response during critical developmental events. Hardness, alkalinity, acidity, light intensity, and thermal differences were studied for trait canalization variation in morphometric, meristic, ontogenetic processes, and pigment characteristics. Trait canalization was observed with no statistical differences (p > 0.05) in mixed random two-way ANOVA comparisons between various block and treatment effects for hardness, alkalinity or acidity. Thermal block variation differences in six measures, including mandible length, yolk sac length, midpostanal depth, and head width, incubation, and hatching length, varied significantly (p ≤ 0.05) with declining temperatures. Water quality and thermal attributes exhibited trait canalization and did not increase character state variation in the early life stage morphological expression, which result in stable phenotypic inheritance rather than variable environmental conditions during embryonic and larval development.