Data from - An assessment of the spatial and temporal variability of biological endpoint responses of rainbow darter collected along an urban gradient.

Municipal wastewater effluent (MWWE) and its constituents,
such as chemicals of emerging concern, pose a potential threat to the
sustainability of fish populations by disrupting key endocrine functions in
aquatic organisms. While studies have demonstrated changes in biological
markers of exposure of aquatic organisms to groups of chemicals of emerging
concern, the variability of these markers over time has not been sufficiently
described in many wild fish species. The aim of this study was to assess the spatial
and temporal variability of biological markers in response to MWWE exposures
and to test the consistency of these same responses between seasons and among
years. Rainbow darter (Etheostoma caeruleum) were collected
in spring and fall seasons over a five-year period in the Grand River, ON,
Canada. In addition to surface water chemistry (nutrients and selected
pharmaceuticals), measures were taken across levels of biological organization
in rainbow darter. The measurement of hormone production, gonad development,
and intersex severity were temporally consistent and suggested impaired
reproduction in male fish collected downstream of MWWE outfalls.  In contrast, ovarian development and hormone
production in females appeared to be influenced more by urbanization than MWWE.
 Measures of gene expression and somatic
indices were highly variable between sites and years respectively, and were
inconclusive when determining the impacts of MWWE overall. Robust biomonitoring
programs must consider these factors in both the design and interpretation of
results, especially when spatial and temporal sampling of biological endpoints
is limited.  Assessing the effects of contaminants
and other stressors on fish in watersheds would be greatly enhanced by an
approach that considers natural variability in the endpoints being measured.