NEW ORLEANS (AP) -- Contrary to public perception that last summer's BP oil spill did little damage to marine life in Louisiana, a new study says a common fish in the marshes was hurt severely by the spill and now is turning up deformed and may be unable to reproduce properly.The study, led by a team of scientists from Louisiana State University, found what scientists call "sub-lethal" effects to killifish, a small but abundant species found in Louisiana's marshes and used as bait by fishermen. Sub-lethal effects are those that pop up as animals grow. Researchers said the fish are showing signs of damage even though the amount of oil in their tissues and in the water where they were sampled was extremely low or not even detectable.The findings were published this week in the Proceedings of the National Academy of Sciences journal.By looking at killifish sampled near Grand Terre, a barrier island in the heavily oiled Barataria estuary, the scientists said they found physiological and reproductive impairments. The scientists said the gills, intestines and cardiovascular organs of the fish have been damaged. The researchers also said the fish they looked at are now smaller than they should be."They are essentially listless, the ones from the oiled sites," said Fernando Galvez, a fish biologist at LSU. "These animals are hurting pretty badly."Galvez said fish in the embryonic stage were affected the most and are not growing properly. He said the study published this week focused on what effects were found in the first four months after the spill, but he said the group of researchers has tracked the progress of killifish since the spill and found lingering problems.This study took a different tack than previous studies that sought to find evidence of trouble by measuring oil contamination. Instead, the LSU researchers looked for changes in fish genes caused by contamination."Just measuring the chemistry in the water and also in the fish is not going to provide much useful information in terms of looking at the true actual effects on the fish," Galvez said."We have done all this chemical testing of wildlife, seafood and water and the message has gone out that seafood from Louisiana is safe to eat," said Andrew Whitehead, an LSU genome researcher who worked on the study. "The message is that the animals are out of the woods because they are not carrying a chemical burden. But when you ask the fish directly, when you look at their biology, they show that they have been exposed and that may be a problem for populations."Galvez said their findings are similar to what scientists found after the Exxon-Valdez spill, where subtle but serious problems took several years before they were noticed by scientists."Maybe looking for genetic effects is a better way than looking for oil," said Gilbert T. Rowe, a marine ecologist at Texas A&M University at Galveston.Rowe said examining killifish, "a model for things that live in the ocean," was a good choice because they are so abundant. "It's like studying a mouse" to figure out effects on humans, he said.Bernard Rees, a fish physiologist at the University of New Orleans, said the researchers had found an important link between oil contamination and possible physiological effects. He said the most troubling possibility for the long-term health of killifish was the chance that oil contamination harmed reproduction. He said that killifish are an important food source for other fish, including speckled trout and redfish, favorite species for sport fishermen.But Rees said that it was too early to know the long-term effects. "Nature has the capacity to rebound, so we'll have to wait and see if there are any long lasting population effects."The study, which included scientists from Clemson University and Texas State University, was funded by the National Science Foundation and through a fund set up by BP to pay for independent studies of the spill.