Aerial and aquatic respiration of the Australian Desert Goby, Chlamydogius
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Physiological, anatomical and behavioural adaptations enable the Australian desert goby, Chlamydogobius eremius, to live in mound springs and temporary aquatic habitats surrounding the south-eastern rim of the Lake Eyre drainage basin in the harsh inland of Australia. This study describes the desert goby's respiratory and metabolic responses to hypoxic conditions and its use of buccal air bubbles for gas exchange at the water surface. Oxygen consumption for C. eremius is significantly higher in water than in air under normoxic and hypoxic conditions. In water, total oxygen consumption (VO2) increases from normoxic conditions (253 μl g−1 h−1) to 8% ambient O2 concentration (377 μl g−1 h−1), then decreases with increasing hypoxia of 4% O2 (226 μl g−1 h−1) and at 2% O2 (123 μl g−1 h−1). In air (fish were moist but out of water),VO2 progressively decreases from normoxic conditions to hypoxic conditions (21% O2, VO2 is 169 μl g−1 h−1 to 39 μl g−1 h−1 at 2% O2). These data indicate oxygen-conforming patterns with increasing hypoxia both in air and in water below 8% O2. In water, opercular movement rates remain unchanged with increasing hypoxia (139 min−1 at 21% O2, 154 min−1 at 8%, 156 min−1 at 4% and 167 min−1 at 2%) but in air, opercular movement rates are significantly lower than in water, corresponding with the lower metabolic rate (71 min−1 at 21% O2, 53 min−1 at 8%, 96 min−1 at 4% and 64 min−1 at 2%). Chlamydogobius eremius can use a buccal air bubble for aerial O2 uptake, most probably in response to increased aquatic hypoxia. In air, C. eremius relies more on the buccal bubble as an oxygen source with increasing hypoxia up to an ambient O2 of 4% (7.1% of VO2 at 21% O2; 14.5% at 8% O2; and 27.1% at 4% O2), then when the available supply of O2 is further reduced, it decreases (15% of VO2 at 2% O2) and respiration across the skin again makes a higher relative contribution. The Australian desert goby has a higher metabolic rate in higher salinities (336 μl g−1 h−1 in 35 ppt, 426 μl g−1 h−1 in 70 ppt) than in freshwater (235 μl O2 g−1 h−1), presumably because of the increased metabolic cost of osmoregulation. There was no significant difference VO2 in for fish in air that had come from varying salinities.