Reduced predator avoidance follows ocular and lateral line pathology in minnow species after diesel exposure.

Petroleum chemicals reach freshwater habitats and can elicit acute toxic effects on ecosystem members.1Until recently standardized acute toxicology experiments and water quality standards (also referred to as Maximum Allowable Concentrations in some jurisdictions) focused on mortality of aquatic organisms after 96 h of toxicant exposure2,3, but in nature sublethal effects can manifest into mortality and in lotic environments (streams and rivers) exposure times can be far shorter (< 24 h). Here we show that Plains Minnow (Hybognathus placitus), Fathead Minnow (Pimephales promelas), and Flathead Chub (Platygobio gracilis) (Family Leuciscidae) exposed to sublethal concentrations of diesel fuel for 24 h experienced sublethal injuries which render them susceptible to death by predation. Diesel-exposed prey represented 77% of predated fish across all predation events. Decreased predator avoidance likely arose from sensory impairment. Diesel-exposed Fathead Minnow had significantly decreased lateral line neuromast counts and severe ophthalmic pathology. Standardized toxicity experiments would have missed these key effects. Sublethal petroleum exposures have global implications for the conservation of fish species and derivations of water quality standards intended to protect fish from petrochemical pollution need to include sublethal endpoints with the potential to manifest into population loss.