title: The contribution of air breathing to aerobic scope and exercise performance in the banded knifefish Gymnotus carapo L.
abstract: The contribution of air breathing to aerobic metabolic scope and exercise performance was investigated in a teleost with bimodal respiration, the banded knifefish, submitted to a critical swimming speed (U(crit)) protocol at 30°C. Seven individuals (mean ± s.e.m. mass 89±7 g, total length 230±4 mm) achieved a U(crit) of 2.1±1 body lengths (BL) s(-1) and an active metabolic rate (AMR) of 350±21 mg kg(-1) h(-1), with 38±6% derived from air breathing. All of the knifefish exhibited a significant increase in air-breathing frequency (f(AB)) with swimming speed. If denied access to air in normoxia, these individuals achieved a U(crit) of 2.0±0.2 BL s(-1) and an AMR of 368±24 mg kg(-1) h(-1) by gill ventilation alone. In normoxia, therefore, the contribution of air breathing to scope and exercise was entirely facultative. In aquatic hypoxia (P(O(2))=4 kPa) with access to normoxic air, the knifefish achieved a U(crit) of 2.0±0.1 BL s(-1) and an AMR of 338±29 mg kg(-1) h(-1), similar to aquatic normoxia, but with 55±5% of AMR derived from air breathing. Indeed, f(AB) was higher than in normoxia at all swimming speeds, with a profound exponential increase during exercise. If the knifefish were denied access to air in hypoxia, U(crit) declined to 1.2±0.1 BL s(-1) and AMR declined to 199±29 mg kg(-1) h(-1). Therefore, air breathing allowed the knifefish to avoid limitations to aerobic scope and exercise performance in aquatic hypoxia.
authors.affiliation: Departamento de Zoologia, Instituto de Biociências, Universidade Estadual Paulista, Campus Rio Claro, 13506-900 Rio Claro - SP, Brazil. david.mckenzie@univ-montp2.fr
authors.forename: David J
authors.initials: DJ
authors.lastname: McKenzie
authors.forename: John F
authors.initials: JF
authors.lastname: Steffensen
authors.forename: Edwin W
authors.initials: EW
authors.lastname: Taylor
authors.forename: Augusto S
authors.initials: AS
authors.lastname: Abe
mesh_terms: D000332:Aerobiosis; D000388:Air; D000818:Animals; D023702:Gymnotiformes / Q000502:physiology*; D000860:Hypoxia; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal; D012119:Respiration; D013550:Swimming