Continuous measurement of oxygen tensions in the air-breathing organ of Pacific tarpon (Megalops cyprinoides) in relation to aquatic hypoxia and exercise.
The Pacific tarpon is an elopomorph teleost fish with an air-breathing organ (ABO) derived from a physostomous gas bladder. Oxygen partial pressure (PO(2)) in the ABO was measured on juveniles (238 g) with fiber-optic sensors during exposure to selected aquatic PO(2) and swimming speeds. At slow speed (0.65 BL s(-1)), progressive aquatic hypoxia triggered the first breath at a mean PO(2) of 8.3 kPa. Below this, opercular movements declined sharply and visibly ceased in most fish below 6 kPa. At aquatic PO(2) of 6.1 kPa and swimming slowly, mean air-breathing frequency was 0.73 min(-1), ABO PO(2) was 10.9 kPa, breath volume was 23.8 ml kg(-1), rate of oxygen uptake from the ABO was 1.19 ml kg(-1) min(-1), and oxygen uptake per breath was 2.32 ml kg(-1). At the fastest experimental speed (2.4 BL s(-1)) at 6.1 kPa, ABO oxygen uptake increased to about 1.90 ml kg(-1) min(-1), through a variable combination of breathing frequency and oxygen uptake per breath. In normoxic water, tarpon rarely breathed air and apparently closed down ABO perfusion, indicated by a drop in ABO oxygen uptake rate to about 1% of that in hypoxic water. This occurred at a wide range of ABO PO(2) (1.7-26.4 kPa), suggesting that oxygen level in the ABO was not regulated by intrinsic receptors.
Seymour
Roger S
RS
Environmental Biology, School of Earth and Environmental Sciences, University of Adelaide, Adelaide 5005, Australia. roger.seymour@adelaide.edu.au
Farrell
Anthony P
AP
Christian
Keith
K
Clark
Timothy D
TD
Bennett
Michael B
MB
Wells
Rufus M G
RM
Baldwin
John
J
D000388:Air; D000818:Animals; D005336:Fiber Optic Technology; D005399:Fishes / Q000502:physiology*; D000860:Hypoxia / Q000503:physiopathology*; D055100:Optical Fibers; D010100:Oxygen / Q000493:pharmacokinetics*; D010313:Partial Pressure; D012119:Respiration; D015656:Respiratory Mechanics; D012137:Respiratory System / Q000378:metabolism*; D013550:Swimming; D013997:Time Factors
D010100:Oxygen