Fish stress hormones linked to tendency to take the bait

The study, published today in the Journal of Experimental Biology, could impact recreational fishing if anglers are mainly catching fish whose stress levels determine if they are likely to strike at a lure.

"We could potentially be selecting for fish that are harder to catch," Cory Suski, University of Illinois natural resources and environmental sciences professor, said in a press release.

This phenomenon is known as fisheries-induced evolution, which happens when people catch fish with specific traits and leave genetically distinct fish remaining.

Previous studies have shown that by catching only the largest fish, commercial fishing operations may alter the growth patterns of the fish that are not caught, causing smaller fish in the population.

Those studies focused on personality traits such as aggression or boldness, but the current study has found that stress hormones are likely the cause.

"When it encounters a challenge or novel situation, a fish's adrenaline shoots up, and that individual is more likely to attack or run away," said Michael Louison, a researcher at the University of Illinois. "But if an animal shows a relatively high cortisol response and a low adrenaline response, they're more likely to freeze."

Researchers took blood samples from 113 largemouth bass, exposed the fish to the open air for three minutes, and then returned them to the water where they recovered for a period of time before a second blood sample was taken.

The researchers found a substantial link between stress-related cortisol levels in the fish and their likelihood of being captured by angling. Cortisol levels tested after the stressor were 48 percent higher in fish that were never caught compared to those that had been caught and returned.