Compensatory response of fathead minnow larve following a pulsed in-situ exposure to a seasonal agricultural runoff event

Authors: ALI, JONATHAN - University Of Nebraska; Sangster, Jodi; SNOW, DANIEL - University Of Nebraska; BARTLET-HUNT, SHANNON - University Of Nebraska; KOLOK, ALAN - University Of Nebraska

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2017
Publication Date: 4/3/2017
Citation: Ali, J.M., Sangster, J.L., Snow, D.D., Bartlet-Hunt, S.L., Kolok, A.S. 2017. Compensatory response of fathead minnow larve following a pulsed in-situ exposure to a seasonal agricultural runoff event. Science of the Total Environment. 603:817-826. doi: 10.1016/j.scitotenv.2017.03.093.

Interpretive Summary: Agriculturally impacted waterways such as those found throughout the Midwestern United States often experience seasonal pulses of agrichemical contaminants which pose a potential hazard to aquatic organisms at various life stages. Many common agrichemicals have been shown to cause endocrine effects in aquatic organisms which may be of especial concern during early developmental stages as growth, metabolism, and survival as well as sexual differentiation are regulated through the endocrine system. The objective of this study was to characterize the developmental plasticity of fathead minnow larvae in a natural environment subject to a seasonal episodic stressor. Fathead minnow larvae were maintained at the Elkhorn River Research Station for a 28-d field exposure to an agrichemical pulse event. Minnow larvae were sampled after 14 and 28 days to characterize developmental plasticity through growth measures and relative gene expression. Elevated concentrations of acetochlor, atrazine, and metachlor were measured in both water and sediments during the pulse and were associated with reductions in body mass, condition factor, and androgenic gene expression in river exposed fathead minnow larvae. However, following a 14-d depuration during the post-pulse period, river exposed larvae overcompensated in previously suppressed biological endpoints. To our knowledge, this is the first study to characterize compensation of larval fish following an episodic exposure to seasonally occurring agrichemical stressors in the field and illustrates the importance of field-based studies for understanding the impacts of natural, composite exposures, as these are events that are not readily simulated under laboratory conditions. Results of this study may help natural resource managers and agrichemical users make better management decisions related to the timing and location of chemical use in relation to sensitive habitats. Improving the health of our aquatic systems will benefit not only fish and wildlife, but everyone who uses these resources for both work and recreation.

Technical Abstract: Agriculturally-dominated waterways such as those found throughout the Midwestern United States often experience seasonal pulses of agrichemical contaminants which pose a potential hazard to aquatic organisms at varying life stages. The objective of this study was to characterize the developmental plasticity of fathead minnow larvae in a natural environment subject to a seasonal episodic stressor. Fathead minnow larvae were maintained at the Elkhorn River Research Station for a 28-d in situ exposure to an agrichemical pulse event. Minnow larvae were sampled over after 14 and 28 days to characterize developmental plasticity through growth measures and relative gene expression (i.e. RT-qPCR). Concentrations of agrichemical contaminants, i.e. herbicides, found in water (POCIS) and sediment samples throughout the 28-d exposure were quantified using gas chromatography-mass spectrometry. Elevated agrichemical concentrations during the pulse were associated with reductions in body mass, condition factor and androgenic gene expression in river exposed fathead minnow larvae. However, following a 14-d in situ depuration during the post-pulse period, river exposed larvae overcompensated in previously suppressed biological endpoints. These results indicate that fathead minnow larvae are capable of compensatory responses following episodic exposure to agrichemical stressors.