title: Changes in cardiac output during swimming and aquatic hypoxia in the air-breathing Pacific tarpon.
abstract: Pacific tarpon (Megalops cyprinoides) use a modified gas bladder as an air-breathing organ (ABO). We examined changes in cardiac output (V(b)) associated with increases in air-breathing that accompany exercise and aquatic hypoxia. Juvenile (0.49 kg) and adult (1.21 kg) tarpon were allowed to recover in a swim flume at 27 degrees C after being instrumented with a Doppler flow probe around the ventral aorta to monitor V(b) and with a fibre-optic oxygen sensor in the ABO to monitor air-breathing frequency. Under normoxic conditions and in both juveniles and adults, routine air-breathing frequency was 0.03 breaths min(-1) and V(b) was about 15 mL min(-1) kg(-1). Normoxic exercise (swimming at about 1.1 body lengths s(-1)) increased air-breathing frequency by 8-fold in both groups (reaching 0.23 breaths min(-1)) and increased V(b) by 3-fold for juveniles and 2-fold for adults. Hypoxic exposure (2 kPa O2) at rest increased air-breathing frequency 19-fold (to around 0.53 breaths min(-1)) in both groups, and while V(b) again increased 3-fold in resting juvenile fish, V(b) was unchanged in resting adult fish. Exercise in hypoxia increased air-breathing frequency 35-fold (to 0.95 breaths min(-1)) in comparison with resting normoxic fish. While juvenile fish increased V(b) nearly 2-fold with exercise in hypoxia, adult fish maintained the same V(b) irrespective of exercise state and became agitated in comparison. These results imply that air-breathing during exercise and hypoxia can benefit oxygen delivery, but to differing degrees in juvenile and adult tarpon. We discuss this difference in the context of myocardial oxygen supply.
authors.affiliation: Environmental Biology, School of Earth and Environmental Sciences, University of Adelaide, Adelaide 5005, Australia. timothy.clark.mail@gmail.com
authors.forename: T D
authors.initials: TD
authors.lastname: Clark
authors.forename: R S
authors.initials: RS
authors.lastname: Seymour
authors.forename: K
authors.initials: K
authors.lastname: Christian
authors.forename: R M G
authors.initials: RM
authors.lastname: Wells
authors.forename: J
authors.initials: J
authors.lastname: Baldwin
authors.forename: A P
authors.initials: AP
authors.lastname: Farrell
mesh_terms: D000375:Aging / Q000097:blood; D000400:Air Sacs / Q000378:metabolism / Q000503:physiopathology*; D000818:Animals; D002302:Cardiac Output; D005399:Fishes / Q000097:blood*; D006339:Heart Rate; D000860:Hypoxia / Q000097:blood / Q000503:physiopathology*; D015876:Northern Territory; D010100:Oxygen / Q000097:blood*; D005082:Physical Exertion; D015656:Respiratory Mechanics; D013318:Stroke Volume; D013550:Swimming; D013997:Time Factors
chemical_list: D010100:Oxygen