Exposure to ultraviolet radiation late in development increases the toxicity of oil to mahi-mahi (Coryphaena hippurus) embryos

The Deepwater Horizon oil spill in 2010 overlapped with the spawning of many pelagic fish species in the Gulf of Mexico, including mahi-mahi (Coryphaena hippurus). PAH released during the spill have been shown to cause photo-induced toxicity under UV radiation. To verify this, mahi-mahi embryos were exposed to high-energy water accommodated fractions of source and naturally weathered oils for up to 48 h. The co-exposure timing with UV radiation varied between an early development exposure for 8 hr or a late development exposure for 8 hr. The UV co-exposure had a photo-induced toxic effect on hatching success for all oil types and exposure scenarios. A more sensitive developmental window to photo-induced toxicity was observed when UV exposure occurred late in development. Source Oil B was over six-fold more toxic, and Massachusetts source oil was 1.6-fold more toxic when the embryos were co-exposed to UV light late in development. Weathered oil from the surface co-exposure with UV late in development resulted in bradycardia in the mahi-mahi.