title: The aerobic physiology of the air-breathing blue gourami, Trichogaster trichopterus, necessitates behavioural regulation of breath-hold limits during hypoxic stress and predatory challenge.
abstract: Physiological characteristics of the blood oxygen transport system and muscle metabolism indicate a high dependence on aerobic pathways in the blue gourami, Trichogaster trichopterus. Haemoglobin concentration and haematocrit were modest and the blood oxygen affinity (P50=2.31 kPa at pH 7.4 and 28 degrees C) and its sensitivity to pH (Bohr factor, phi=-0.34) favour oxygen unloading at a relatively high oxygen pressure (PO2). The intracellular buffering capacity (44.0 slykes) and lactate dehydrogenase (LDH) activity (154.3 iu g(-1)) do not support exceptional anaerobic capabilities. Air-breathing frequency in the blue gourami is expected to increase when aquatic oxygen tensions decline. Under threat of predation, however, this behaviour must be modified at a potential cost to aerobic metabolism. We therefore tested the hypothesis that metabolic responses to predatory challenge and aquatic hypoxia are subject to behavioural modulation. Computer-generated visual stimuli consistently reduced air-breathing frequency at 19.95, 6.65 and 3.33 kPa PO2. Bi-directional rates of spontaneous activity were similarly reduced. The metabolic cost of this behaviour was estimated and positively correlated with PO2 but not with visual stimulation thus indicating down-regulation of spontaneous activity rather than breath-holding behaviour. Neither PO2 nor visual stimulation resulted in significant change to muscle lactate and ATP concentrations and confirm that aerobic breath-hold limits were maintained following behavioural modulation of metabolic demands.
authors.affiliation: School of Biological Sciences, The University of Auckland, New Zealand. n.herbert@auckland.ac.nz
authors.forename: N A
authors.initials: NA
authors.lastname: Herbert
authors.forename: R M
authors.initials: RM
authors.lastname: Wells
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000244:Adenosine Diphosphate / Q000097:blood; D000255:Adenosine Triphosphate / Q000097:blood; D000388:Air; D000818:Animals; D004779:Environment Design; D005399:Fishes / Q000502:physiology*; D006160:Guanosine Triphosphate / Q000097:blood; D006454:Hemoglobins; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007773:Lactates / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D010100:Oxygen / Q000097:blood; D010108:Oxyhemoglobins / Q000378:metabolism; D011235:Predatory Behavior; D012119:Respiration; D013312:Stress, Physiological / Q000378:metabolism / Q000503:physiopathology*
chemical_list: D006454:Hemoglobins; D007773:Lactates; D010108:Oxyhemoglobins; D000244:Adenosine Diphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D010100:Oxygen