Fish embryos exposed to oiled sediment in a laboratory setting, even when the oil isn’t visible, take longer to hatch and those that do hatch have deformities like elongated hearts, according to an article in the peer-reviewed science journal Environmental Science and Technology.

In addition, the scientific article states that adult Gulf killifish collected in the wild also show differences based on whether they were in an oiled or unoiled area. The changes were measured by looking at the “turning on” of a gene in the bait fish indicating exposure to oil even a year after oil was no longer visible in an area.

The results could have implications for other fish species that breed or live in Louisiana’s coastal marshes such as red fish, snapper or shrimp, researchers said.

Andrew Whitehead, assistant professor of environmental toxicology for the University of California at Davis, said animals that share a common habitat with the Gulf killifish, a common small bait fish in coastal Louisiana, share a similar risk.

However, he said, that doesn’t mean Gulf seafood is unsafe to eat.

“Almost no detectable oil in the water, no detectable oil in the tissue, it’s safe to eat,” Whitehead said. “But there are still developmental difficulties.”

The message that seafood from the Gulf is safe to eat has had unintended consequences by leading people to believe everything is okay in the fisheries when “that doesn’t appear to be the case,” he said.

Although the tests were only done on the Gulf killifish, it could point to other problems.

“We can’t test all the species at the same time, that’s why we use the Gulf killifish,” said Benjamin Dubansky, a recent LSU doctorate graduate and one of the authors of the article. “We found effects persist long after the visible oil is gone.”

The two-part look at the impacts the Deepwater Horizon could be having on fisheries first set out to determine if oil in sediment is having an impact on fish. The answer to that was yes by looking at the genetic reaction to oil exposure.

Genes turn on or off depending on what they need the body to do, and specific genes react in specific ways to certain chemical exposures, Whitehead said.

“We can see what cellular programs are running,” he said.

The tests on the adult Gulf killifish collected in oiled and unoiled areas showed a difference on this genetic level of oil exposure, he said.

The second part of the work looked at the possibility of impacts to the early life stages of the fish by bringing sediment from oiled and unoiled areas into the labs and placing embryos in the sediment and water mix.

“We were worried about the early life stage because we know the early life stages are vulnerable to impacts of oil,” Whitehead said.

What they found is that the oiled sediment embryos didn’t have as much success in hatching; those that did hatch were delayed and many of those had deformities.

“We’re not saying the killifish are circling the drain by any means,” Whitehead said.

In fact, one of the unknowns is how much populations of the fish in unoiled areas can make up for issues experienced in oiled areas, he said.

“The population dynamics is something we don’t really know well for this species,” he said.

Fernando Galvez, LSU associate professor in the Department of Biological Sciences and another author of the paper, agreed that what is seen with the impact of oil on the Gulf killifish is something that has been documented in other areas.

“Other animals show similar effects when they’re exposed to crude oil,” he said.

Essentially, the long-term exposure of fish to the continuing presence of polycyclic aromatic hydrocarbons in the soil reduces the health of fish embryos and could predict future problems with fish population numbers, according to the article.

Other authors of the report include Jeffrey Miller with the UC Davis Department of Environmental Toxicology and Charles D. Rice, professor in the Department of Biological Sciences at Clemson University.

Funding for the work included in the paper came from the National Science Foundation and the Gulf of Mexico Research Initiative.