Hakai Magazine —
Imagine you are quietly reading this story at home when—bang—you hear a loud crash nearby. You whirl your head toward the sound—a behavioral response—while your heart starts racing—a physiological response. These stress responses can mean the difference between life and death.
How these processes play out in the brains of humans and other mammals is well understood. But for fish, these pathways from the brain to behavior have largely been a mystery. Previous research shows that fish do, of course, react to external stressors. But new research reveals that fish’s brains regulate stress responses in a similar way to mammals’ brains.
Marco Cerqueira, a marine biologist at the University of Algarve in Portugal, investigated these stress responses by testing how European sea bass react to two types of stress: predictable and unpredictable. In training sessions, Cerqueira and his colleagues taught the fish to associate a visual cue, a black-and-yellow-striped card, with a stressor, a mesh net like the ones used to catch fish in aquaculture operations. The fish in the predictable group always saw the card a minute before the net swept through the fish tank, a signal of the impending stress. The fish subjected to unpredictable stress had no such warning: the card was displayed randomly before or after the net.