Stress in rainbow trout

Authors: Mekaa, J, McCormick, S
Journal: Fisheries Research 72 311–322
Year: 2005
Where:
1. United States Geological Survey, Anchorage, USA
2. United States Geological Survey, Conte Anadromous Fish Research Center, Massachusetts, USA

An increase in the hormone cortisol is a well documented indicator of stress in animals, including humans and fish. This research found that after just 2 minutes of angling, cortisol levels increased significantly. Handling by fishermen adds to the physiological pressure put on the fish. After the encounter with the angler, it took up to 24 hours for the cortisol to return to a normal level.

Repeated hooking cumulatively adds to the harm done to the fish. About a third of the fish population studied in this research showed scars caused by an angler’s hook.

Two percent of the fish in the study died straight away from the damage done by hooking. This, the researchers say, was probably due to significant bleeding.


"This study evaluated the immediate physiological response of wild rainbow trout to catch-and-release angling in the Alagnak River, southwest Alaska. Information was recorded on individual rainbow trout (n = 415)."

SIGNS OF STRESS AFTER 2 MINUTES OF CAPTURE BY ANGLERS

"Levels of plasma cortisol and lactate in extended capture fish (angling duration greater than 2 min) were significantly higher than levels in rapid capture fish (angling duration less than 2 min). Rapid capture fish were significantly smaller than extended capture fish, reflecting that fish size influenced landing and handling times."

EACH TIME FISH CAUGHT ADDS TO DAMAGE TO HEALTH

"Physiological disruptions from stress events can be considered cumulative; therefore, it is possible that fish caught and released several times during a fishing season may be more vulnerable to these types of sublethal effects."

"Approximately 30% of Alagnak River rainbow trout have at least one scar purportedly due to previous hooking, indicating that a substantial portion of the population is subjected to multiple angling captures."

"Immediate mortality was observed in seven fish (2%, n = 7/415) that most likely died due to hooking injuries that produced significant bleeding."

"Increasing angling duration produced a significant increase in levels of plasma cortisol and lactate during each year of the study."

STRESS ADDS TO DEATH RATE

"Capture by angling is one of the most physically demanding forms of exercise stress in fish and the subsequent physiological response has been demonstrated to increase with the amount of time fish are on the hook, sometimes resulting in high mortality rates"

HANDLING FISH DURING HOOK REMOVAL ADDS TO STRESS LEVELS

"Handling stress during the hook removal process is a concern among researchers examining the response of fish to angling. We suggest that the initial slope of increase for levels of plasma cortisol and lactate in extended capture fish following landing and handling stress represents the early stages of a stress response that will continue to increase. Indeed, all of the physiological variables that we measured peaked some time after the stressor had been applied."

"In general, the amount of time required for plasma cortisol to recover to resting levels following an acute stress event is within 24 h."
Fish Pain