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

The timing of the Deepwater Horizon oil spill in 2010 overlapped with the spawning of many pelagic fish species in the Gulf of Mexico, including the mahi mahi (Coryphaena hippurus). Polycyclic aromatic hydrocarbons (PAHs) released during the spill have been shown to cause photo-enhanced toxicity under ultraviolet (UV) radiation. Mahi mahi eggs are positively buoyant and transparent, making these organisms at risk for photo-enhanced toxicity. In this study, mahi mahi embryos were exposed to high-energy water accommodated fractions (HEWAF) of source and naturally weathered oils for 48 h. The timing of co-exposure with UV radiation varied between an early development exposure occurring at ~8 hpf for 8 h or a late development exposure occurring at ~27 hpf for 8 h. Hatching success was documented at the end of each oil exposure. The UV co-exposure had a photo-enhanced toxic effect on hatching success for all oil types. However, a more sensitive developmental window to photo-enhanced toxicity was observed when UV exposure occurred late in development. Source oil b (SOB) was over six fold more toxic and Massachusetts source oil (MASS) was 1.6 fold more toxic when the embryos were co-exposed to UV light late in development. Further, weathered oil from the surface (OFS) co-exposure with UV late in development resulted in bradycardia in the mahi mahi. This study provides evidence that the developmental window when UV exposure occurs has a significant effect on the degree of photo-enhanced toxicity of oil, as well as provides evidence that UV may exacerbate oil-related cardiac effects in developing fish.