Molecular Genetic Responses and Recovery of Adult Migrating Pacific Salmon to Exercise and Temperature Stress

Pacific salmon face a myriad of stressors throughout their spawning migrations including predation, fisheries, and environmental conditions that push these organisms to their physiological limits.  With increasing river temperatures and a recent shift in fisheries more frequently operating in freshwater, understanding the physiological links between exercise associated with fisheries capture and release at high temperatures is an important conservation issue.  RT-QPCR was used to test a series of stress-related genes to assess the response to and recovery from exercise and temperature stress for adult sockeye (Oncorhynchus nerka) and pink (O. gorbuscha) salmon.  Genes related to cellular stress, apoptosis, and chaperone proteins were selected for investigation.  Following an experimental exercise stress and air exposure, Jun B, NUPR, and Cyto C each significantly increased in relative expression immediately following the stressor, peaked at 4 h, and returned to control values 24 h after the treatment.  Relative to individuals held at 13 and 16 ºC, there was a general upregulation of heat shock proteins (HSPs) and other stress-related genes for sockeye salmon held at 19 ºC, a temperature known to result in high mortality for some populations of migrating sockeye salmon.  Jun B, NUPR, Cyto C, and Coll A3 increased and HSPs decreased in relative expression for moribund fish.  Regardless of temperature treatment, Jun B and NUPR showed decreased expression 48 h following the exercise stressor.  The same general trends were observed between gill and muscle tissues, sexes, and species.  This study identifies molecular processes that are linked with stress response, recovery, and mortality and helps to identify potential biomarkers relating to the interaction of exercise stress and temperature for migrating Pacific salmon.