WASHINGTON — Gulf seafood is safe to eat and the water is clear after the BP oil spill, but a new biology study released Monday shows that effects of the oil on a small Louisiana marsh fish could be an early warning sign of trouble ahead for fish populations.
The study of the little killifish found biological changes that could indicate future problems with development and reproduction. Scientists detected the same cellular changes in herring and other animals after the Exxon Valdez spill in Alaska and before populations crashed.
"The message that seafood is safe to eat doesn't necessarily mean that the animals are out of the woods," said Andrew Whitehead, an assistant professor of biology at Louisiana State University and a lead researcher in the study, which was published this week in the Proceedings of the National Academy of Sciences.
The researchers measured cellular responses in the liver tissue that showed which genes were being turned on and off. Those patterns allowed researchers to predict problems of health and reproduction.
Never miss a local story.
The responses were detected even though the water was clean and only very low or non-detectable concentrations of oil components showed up in fish tissues.
"Where's the oil? It's in the sediments," Whitehead said. Scientists assume that fish can be exposed when waves and storms stir sediments up.
The study found the same kind of cellular responses in killifish as were observed in herring, salmon and other animals that later had large population losses as a result of the Exxon Valdez spill, Whitehead said.
It will take several years, however, before it will be known whether the population of Louisiana killifish, an important food for other fish, actually declines, Whitehead said.
"Ultimately, that's what we're interested in — the population consequences over the long term," he said.
The researchers found that when they exposed developing fish embryos to the same water and sediment in the lab, they showed the same cellular responses.
They also found that the gill tissues weren't healthy. The gills are important for helping the fish compensate for changes in its environment such as shifts in temperature and levels of salt and oxygen in the water, Whitehead said.
Doug Inkley, a senior scientist with the National Wildlife Federation, said the killifish, also known as the bull minnow or cacahoe, was an important part of the food chain.
"This study is alarming because similar health effects seen in fish, sea otters and harlequin ducks following the Exxon Valdez spill in Alaska were predictive of population impacts, from decline to outright collapse," he said in a statement.
The study "is a reminder that even small amounts of oil can have a large and lasting impact on individual fish and wildlife," he said.
MORE FROM MCCLATCHY
Follow Renee Schoof on Twitter.