EcoToxChip reveals immune and metabolic pathway disruption in fish chronically exposed to stormwater-impacted environments

Urban stormwater runoff is a growing concern for aquatic ecosystems because it contains complex mixture of nutrients and chemical contaminants. This study assessed molecular and physiological responses in wild fathead minnows (Pimephales promelas) in the stormwater-dominated Nose Creek Watershed, Alberta, Canada. Adult fish were sampled from multiple sites ranging from agriculturally influenced sites to urban-impacted reaches, during the pre-spawning period in May and post-spawn in September 2023. Water quality parameters and fish health endpoints (e.g. condition factor, liversomatic, and gonadosomatic indices) were measured alongside gene expression profiling using the EcoToxChip platform. Results revealed significant differences in liver and gonad sizes among the sampling sites. Transcriptomic analysis showed differential expression in pathways related to xenobiotic metabolism (e.g., cytochrome P450 1A, glutathione S-transferase C-terminal domain (gstcd), stress response (heat shock protein 70.3, heat shock protein family A member 9 (hspa9)), immune function (T helper 17 cells, T helper 1, and T helper 2 cell differentiation), lipid metabolism (peroxisome proliferator-activated receptor signaling), and apoptosis (caspase 9, growth arrest and DNA-damage-inducible protein 45 gamma a). Upstream West Nose Creek exhibited signs of degradation in few water quality parameters, raising concerns about its continued suitability as a minimally impacted reference site. The study highlights the utility of combining molecular new approach methods (NAMs) with traditional health endpoints to assess the sub-lethal effects of urban stormwater and supports the integration of targeted transcriptomics into environmental monitoring frameworks.