Exposure to even tiny amounts of copper can impair a salmon’s ability to detect and evade predator species, a new study has found. While salmon typically become still and alert after they smell a compound called Schreckstoff, which is released when a fish is damaged nearby, Washington State University (WSU) researchers say fish exposed to just five parts of copper per billion are unable to detect the substance, making them more vulnerable to attack. In a series of tests conducted in a four-foot diameter tank, salmon that weren’t exposed to copper would freeze after smelling the Scheckstoff, delaying by 30 seconds, on average, attack from cutthroat trout also swimming in the tank. Fish swimming in tanks containing copper, however, continued to swim, and were attacked by predators in about five seconds. “A copper-exposed fish is not getting the information it needs to make good decisions,” said Jenifer McIntyre, a WSU researcher and lead author of the study, published in the journal Ecological Applications. These findings could mean that fish could face greater risk in the wild after exposure to copper from stormwater runoff or mining operations.