As juvenile reef fishes develop, they are vulnerable to predators, so much so that typically less than 10 percent of the larvae and embryos survive to adulthood. Those that do have to learn to distinguish between friend and foe, as well as adopt certain behaviors that increase their level of safety, like traveling in groups, minimizing movement in open water and quickly fleeing from perilous situations.

However, a new study published in the Nature Ecology & Evolution journal has shown that for fishes that have been exposed to oil, such abilities became consistently impaired. Six different fish species were involved in the study.

“In several different experiments, the fish exposed to oil exhibited very risky behavior, even in the presence of a predator," said Andrew Esbaugh, an assistant professor of marine science at The University of Texas Marine Science. He and colleague Jacob Johansen had led a team of fisheries biologists in the study.

Earlier research that examined the impact of oil on the physiology of fishes, but this is the first study to show that oil exposure affects behavior such that predation of the fishes is increased. Their growth, survival and ability to locate suitable habitats were found to be negatively affected as well.

In addition, the corals that depend on the fishes are also negatively affected, as most reefs rely on fishes to remove the algae that can restrict their growth and development.

The research team took care to ensure that the concentrations of oil used in the study mimicked those in the real world. “We used oil concentrations that are already present in many industrialized regions worldwide—concentrations that ranged from two to five parts per billion, the equivalent of a couple of drops in a swimming pool," Johansen said.

Besides highlighting the detrimental effects of oil on the abilities of fishes, the study shows that it would be essential to minimize oil-based industrial activities near reefs to ensure the preservation of the reef.