Optimization of effects-assessment of greenside darter (Etheostoma blennioides) exposed to tertiary treated municipal wastewater based on seasonal changes of reproductive endpoints.

The present study describes the seasonal changes in reproductive endpoints of the greenside darter (Etheostoma blennioides) and its implications for environmental monitoring. Fish collections conducted at the appropriate time for the site-specific sentinel fish species can provide a wide variety of population-level information including recruitment, reproduction, and energy storage. The objectives of the present study were to: 1) characterize seasonal changes in reproductive endpoints of the greenside darter (both sexes) to determine the appropriate period for monitoring of this sentinel species; and 2) evaluate the effect of exposure of this sentinel species to tertiary treated municipal effluent at the selected monitoring period. Based on the selected parameters (gonadosomatic index [GSI], liver somatic index [LSI], condition factor, and in vitro gonadal steroid production [testosterone (T) in both sexes; estradiol (E2) in females; and 11-ketotestosterone (11KT) in males]), the present study provides evidence for the value of collecting darters during recrudescence (late fall/early winter) to ensure temporal stability, minimum variability, and stable steroid production capacity. Darters exposed to tertiary treated municipal effluent tended to be larger and heavier relative to reference fish but did not demonstrate any consistent responses in terms of condition or relative liver size. No effect on gonadal development was observed, even though these tertiary-effluent-exposed fish demonstrated a significant reduction in the ability to produce hormones. The present study suggests that although fish exposed to tertiary treated effluent demonstrate no population-level effects, they are still responding at a physiological level. Documentation of the reproductive cycle of sentinel species allows for selection of the most appropriate sampling period to reduce variability and greatly enhances the reliability and interpretation of biological responses.