Assessing the Kynurenine–Tryptophan Ratio (KTR) and CYP1 Activity in Longnose (Catostomus catostomus) and White Suckers (Catostomus commersonii) Exposed to Petroleum-Derived Contaminants from the Alberta Oil Sands Region

In the Alberta Oil Sands Region (AOSR), environmental stressors linked to oil sands industrial activity may have significant and species-specific impacts on local wildlife. This study evaluated the kynurenine–tryptophan ratio (KTR) as a potential biomarker for environmental exposure in longnose suckers (Catostomus catostomus) and white suckers (Catostomus commersonii) collected from various locations within the AOSR. The relationship between KTR and CYP1 enzyme activity (ethoxyresorufin-O-deethylase; EROD) was assessed alongside biometric indices, including gonadosomatic index (GSI), hepatic somatic index (HSI), and fat content. Both species exhibited increased EROD activity when exposed to oil sands natural deposits and potential industrial activity, indicating significant polycyclic aromatic compound (PAC) exposure. However, KTR changes were species-dependent: longnose suckers showed an inversely proportional relationship between KTR and EROD, while white suckers displayed a directly proportional correlation. Longnose suckers downstream of both municipal waste and industrial activity exhibited significant increases in GSI and fat content, with KTR varying more consistently by location rather than sex, suggesting that KTR may be a more reliable marker for location-based exposure. Species-specific differences in KTR and EROD relationships may be influenced by the distinct environmental requirements of each species, and their differing sensitivities to environmental conditions, including temperature, turbidity and flow conditions, during sampling periods. These findings illustrate the complexity of interpreting environmental biomarkers in wildlife and emphasize the need to consider ecological requirements and environmental conditions. Further research is necessary to validate this biomarker across different years and conditions and enhance its application in environmental monitoring and conservation efforts.