__The bluefin is not the only fish that spawns in the gulf, and while it is often a focus of attention, researchers are worried about the impact of the Deepwater Horizon oil spill on many other species. In fact, scientists say, it is virtually certain that billions of fish eggs and larvae have died in the spill, which came at the worst possible time of the year. Spawning season for many fish in the gulf begins in April and runs into the summer. The drilling rig exploded on April 20, and the spill has since covered thousands of square miles with patches of oil. The environmental advocacy group, the Center for Biological Diversity , in Tucson, filed the request under the Endangered Species Act in late May. If the petition is granted, a process that could take years, the endangered listing would require that federal agencies conduct exhaustive analysis before taking any action, like granting drilling permits, that would pose additional risk to the fish.