A research team led by scientists at the University of California, Riverside and the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science have found that ultraviolet light is changing the structure of the Deepwater Horizon (DWH) oil components into something more toxic, further threatening numerous commercially and ecologically important fishes. The DWH oil spill, in which more than three million barrels of crude oil got released in 2010 into the northern Gulf of Mexico, is the worst oil disaster in US history, contaminating the spawning habitats for many fishes."Ours is the first experiment evaluating the effects of DWH oil on the genetic responses of mahi-mahi embryos and larvae," said Daniel Schlenk, a professor of aquatic ecotoxicology, who led the study published in Environmental Science and Technology. "It is also the first experiment of this nature on a lifestage and species that was likely exposed to the oil. We found that the weathering of oil had more significant changes in gene expression related to critical functions in the embryos and larvae than the un-weathered oil. Our results predict that there are multiple targets of oil for toxicity to this species at the embryonic life stage."