Physiological benefits of being small in a changing world: responses of Coho salmon (Oncorhynchus kisutch) to an acute thermal challenge and a simulated capture event

• Published in: PloS one 2012-06, Vol.7 (6), p.e39079-e39079
• Main Authors: Clark, Timothy D, Donaldson, Michael R, Pieperhoff, Sebastian, Drenner, S Matthew, Lotto, Andrew, Cooke, Steven J, Hinch, Scott G, Patterson, David A, Farrell, Anthony P
• Format: Article
• Language: English
• Subjects: Age; Air exposure; Analysis; Animal behavior; Animals; Anthropogenic factors; Biochemistry; Biology; Body mass; Body Weight; Climate change; Commercial fishing; Environmental changes; Evolution; Exposure; Female; Females; Fish; Fish populations; Fisheries; Fishes; Fishing; Homeostasis; Male; Males; Metabolic rate; Metabolism; Mortality; Oncorhynchus kisutch; Oncorhynchus kisutch - physiology; Oncorhynchus tshawytscha; Osmoregulation; Oxygen; Oxygen Consumption; Physiological aspects; Physiology; Potassium; Recovery; Salmon; Science; Simulation; Studies; Temperature; Testosterone; Trends; Ventilation
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0039079

Evidence is building to suggest that both chronic and acute warm temperature exposure, as well as other anthropogenic perturbations, may select for small adult fish within a species. To shed light on this phenomenon, we investigated physiological and anatomical attributes associated with size-specific responses to an acute thermal challenge and a fisheries capture simulation (exercise+air exposure) in maturing male coho salmon (Oncorhynchus kisutch). Full-size females were included for a sex-specific comparison. A size-specific response in haematology to an acute thermal challenge (from 7 to 20 °C at 3 °C h(-1)) was apparent only for plasma potassium, whereby full-size males exhibited a significant increase in comparison with smaller males ('jacks'). Full-size females exhibited an elevated blood stress response in comparison with full-size males. Metabolic recovery following exhaustive exercise at 7 °C was size-specific, with jacks regaining resting levels of metabolism at 9.3 ± 0.5 h post-exercise in comparison with 12.3 ± 0.4 h for full-size fish of both sexes. Excess post-exercise oxygen consumption scaled with body mass in male fish with an exponent of b = 1.20 ± 0.08. Jacks appeared to regain osmoregulatory homeostasis faster than full-size males, and they had higher ventilation rates at 1 h post-exercise. Peak metabolic rate during post-exercise recovery scaled with body mass with an exponent of b~1, suggesting that the slower metabolic recovery in large fish was not due to limitations in diffusive or convective oxygen transport, but that large fish simply accumulated a greater 'oxygen debt' that took longer to pay back at the size-independent peak metabolic rate of ~6 mg min(-1) kg(-1). Post-exercise recovery of plasma testosterone was faster in jacks compared with full-size males, suggesting less impairment of the maturation trajectory of smaller fish. Supporting previous studies, these findings suggest that environmental change and non-lethal fisheries interactions have the potential to select for small individuals within fish populations over time.