Diel patterns of baseline glucocorticoids and stress responsiveness in a teleost fish (bluegill, Lepomis macrochirus)

• Published in: Canadian journal of zoology Vol. 92; no. 5; pp. 417 - 421
• Main Authors: COUSINEAU, A, MIDWOOD, J. D, STAMPLECOSKIE, K, KING, G, SUSKI, C. D, COOKE, S. J
• Format: Journal Article
• Language: English
• Published: Ottawa NRC Research Press 01.05.2014; National Research Council of Canada; Canadian Science Publishing NRC Research Press
• Subjects: Animal behavior; Biological and medical sciences; bluegill; circadian cycle; Circadian rhythms; Corticosteroids; cortisol; crapet arlequin; cycle circadien; Fish; Freshwater ecology; Fundamental and applied biological sciences. Psychology; glucose; Lepomis macrochirus; Physiological aspects; réaction de stress; stress response; Teleostei; Thermoregulation. Hibernation. Estivation. Ecophysiology and environmental effects; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Zoological research; Zoology; Canada; Freshwater environment; Lepomis macrochirus; Vertebrata; Pisces; Glucose; Circadian rhythm; Hydrocortisone; Stress
• ISSN: 1480-3283; 0008-4301; 1480-3283; 0008-4301
• DOI: 10.1139/cjz-2014-0054

Little is known about whether glucocorticoids (GC) and GC responsiveness vary on a diel basis in the wild, especially for fish. Using bluegill (Lepomis macrochirus Rafinesque, 1819) as a model freshwater teleost fish, we tested whether baseline concentration and stress responsiveness of GCs (i.e., plasma glucose and cortisol) varied over a 24 h period. Blood samples from lake-dwelling wild bluegill were obtained across six periods representing a complete circadian cycle to determine GC levels in newly captured fish (i.e., within 3 min of capture; baseline), the maximum value (maximum) 45 min following exposure to a standardized aerial exposure stressor, and determining responsiveness (by subtracting minimum from maximum). Our results revealed that baseline glucose concentration did not vary on a diel basis, whereas baseline cortisol concentration did. Maximum and stress-induced glucose responsiveness varied significantly among several time periods with lowest values recorded at midnight and higher values at mid-day. Maximum and stress-induced cortisol responsiveness were consistent across time periods. Collectively, these data suggest that baseline concentrations and stress-induced values of GCs in a freshwater temperate teleost fish tend to be consistent across diel periods such that there is apparently an absence of strong GC diel patterns.