Larval Zebrafish Startle Response Is Highly Sensitive to Crude Oil Exposure

Abstract

Olfaction, vision, and complex behaviors in fish are impacted by oil exposure, but oil effects on neuromasts governing the startle response have not yet been examined. To test the hypothesis that neuromasts would be sensitive to crude oil exposure, we exposed 6-day-old zebrafish (Danio rerio) for 24 h to water-accommodated fractions (WAFs) of source oil from the Deepwater Horizon oil spill. We found reduced startle responses with the lowest observed effect concentration (LOEC) of 1.6 μg ∑50PAH L–1. Reduced incorporation of DASPEI (2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide) suggests impaired detection of sensory stimuli. Neuromasts recovered after 3 days in uncontaminated water, and the startle response recovered with an overshoot suggesting downstream compensation for reduced sensory function after oil exposure. At higher concentrations (54 μg ∑50PAH L–1), the startle response failed to recover while neuromast staining returned to control levels within 3 days post exposure. Thus, at higher exposure concentrations, synaptic and/or postsynaptic processes may also be impacted. The direct exposure of the sensory cells in the neuromasts to ambient water likely explains why the startle response LOEC is among the lowest observed for oil exposure in fish. Since neuromast function is essential for predator avoidance and prey capture, the observed impacts are likely to have fitness consequences.