The biologic response to stress is a dynamic factor of everyday life that
enables an animal to adapt to environmental or psychological demands.5 A stimulus, or
stressor, initiates a series of physiologic reactions involving specific biochemical mediators
of the autonomic nervous system, neuroendocrine axis, and immune system.2 The effects
of these reactions elicit both positive and negative metabolic changes ranging from increased
energy production and immunomodulation, to lethargy, increased morbidity, and immune
dysfunction.2,4 The quantification of the role of stress and its effects on an
animal's well-being has been especially challenging to measure in cetaceans.6 Several
studies have documented levels of cortisol, aldosterone, and leukocyte distribution following
perturbations such as public interaction, handling, and adrenocorticotropic hormone (ACTH)
stimulation in captive and wild cetaceans.1,3,7,8,9 However in cetaceans, cortisol
concentrations vary little except in extreme stress or distress making interpretation of some
results difficult.6 This study was designed to augment those data and to examine, for
the first time, the diagnostic value of using plasma ACTH levels, in addition to other
hematologic and physiologic changes, in detecting stress response-related changes in long-term
This study tests our hypotheses that stress-related parameters (plasma ACTH,
cortisol, aldosterone): 1) follow a diurnal rhythm pattern; 2) become elevated with out-of-water
physical examination; 3) are not elevated during or following periods of wading human contact;
and 4) that plasma ACTH is a more sensitive indicator of stress response-related changes in
longterm captive belugas than cortisol. Three adult belugas, all 19-20 years of age, were
sampled by utilizing trained behavioral fluke presentation for blood collection. This habituated
behavior was used to obtain baseline levels for the analytes of interest. Subsequent blood
collections were obtained at predetermined times throughout the day, during scheduled physical
examinations, and before and after wading-contact sessions to compare to baseline control
Our results demonstrated that plasma ACTH has a diurnal rhythm with the
highest values observed in early morning. Cortisol levels were higher in morning and evening.
Aldosterone levels did not manifest a discernible pattern. Baseline analyte levels were as
follows: plasma ACTH concentrations ranged from 0.3-24.3 pg/ml, serum cortisol from 0.66-4.17
μl/dl, and serum aldosterone from 10-43.6 pg/ml. All stress-related hormones were
significantly elevated during physical examination. Plasma ACTH levels were most increased with
a 5-10 fold elevation during physical examination, whereas cortisol and aldosterone showed only
a 2-4 fold elevation. Stress response analytes from animals involved in wading-contact sessions
did not differ significantly from baseline levels. Correlative hematological and serum chemistry
parameters are currently being analyzed.
To our knowledge, this is the first report of baseline levels of plasma ACTH
in belugas and the first to document changes following a routine perturbation. Moreover, this
study suggests that plasma ACTH, although very labile, is a sensitive indicator of the stress
response that correlates well with the level of perturbation experienced. The results also
support our impression that well-managed wading contact programs are not stressful to the
1. Dold C, J Sweeney, T Reidarson, J McBain, S Monfort. 2000.
Circulating levels of cortisol and aldosterone in the Atlantic Bottlenose Dolphin (Tursiops
truncatus): A comparative look at display animals. Proc. AAZV/IAAAM Joint Conf., p.
2. Moberg GP. 1987. Problems in defining stress and distress in
animals. J. Am. Vet. Med. Assoc., 191(10): 1207-1211.
3. Ortiz RM, GAJ Worthy. 2000. Effects of capture on adrenal
steroid and vasopressin concentrations in free-ranging bottlenose dolphins (Tursiops
truncatus). Comp. Biochem. Phys. Pt. A, 125: 317-324.
4. Raber J. 1998. Detrimental effects of chronic
hypothalamic-pituitary-adrenal axis activation. Mol. Neurobio., 18:1-23.
5. Selye H. 1973. The evolution of the stress concept. Am.
Scientist, (61): 692-699.
6. St. Aubin DJ, L. Dierauf. 2001. Stress and marine mammals. In:
Dierauf, L.A. and F. M. D. Gulland (eds): CRC Handbook of Marine Mammal Medicine. 2nd ed.
CRC Press LLC, pp. 253-269.
7. St. Aubin DJ, JR Geraci. 1989. Adaptive changes in hematologic
and plasma chemical constituents in captive beluga whales, Delphinapterus leucas. Can.
J. Fish. Aquat. Sci., 46(5): 96-803.
8. Aubin DJ, JR Geraci. 1990. Adrenal responsiveness to
stimulation by adrenocorticotropic hormone (ACTH) in captive beluga whales, Delphinapterus
leucas, p. 149-157. In: T. G. Smith, St. Aubin, D.J., and J. R. Geraci [eds.]
Advances in research on the beluga whale, Delphinapterus leucas. Can. Bull. Fish.
Aquat. Sci. pp. 224.
9. St. Aubin DJ, SH Ridgway, RS Wells, H Rhinehart. 1996. Dolphin
thyroid and adrenal hormones: Circulating levels in wild and semidomesticated Tursiops
truncatus, and influence of sex, age, and season. Mar. Mammal Sci., 12(1): 1-13.