"A copper-exposed fish is not getting the information it needs to make good decisions," McIntyre said in a release Tuesday. McIntyre put juvenile coho salmon exposed to varying amounts of copper in tanks with cutthroat trout, a common predator. McIntyre explained salmon are attuned to smell a substance called Schreckstoff, German for "scary stuff," released when a fish is physically damaged, thereby alerting nearby fish to the predator's presence.