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Iversen, N. K., Dupont-Prinet, A., Findorf, I., McKenzie, D. J., & Wang, T. (2010). Autonomic regulation of the heart during digestion and aerobic swimming in the European sea bass (Dicentrarchus labrax). Comp. Biochem. Physiol. A-Mol. Integr. Physiol., 156(4), 463–468.
Résumé: The autonomic regulation of the heart was studied in European sea bass (Dicentrarchus labrax) during digestion and aerobic exercise by measuring cardiac output (Q), heart rate (f(H)), stroke volume (V(s)) and oxygen consumption (MO(2)) before and after pharmacological blockade by intraperitoneal injections of atropine and propranolol. The significant rise in MO(2) (134 +/- 14 to 174 +/- 14 mg kg(-1) h(-1)) 6 h after feeding (3% body mass) caused a significant tachycardia (47.7 +/- 10.9 to 72.6 +/- 7.2 beats min(-1)), but only a small elevation of Q. MO(2) of fasting fish increased progressively with swimming speed (0.7-2.1 BL s(-1)) causing a significant tachycardia (43 +/- 6 to 61 +/- 4 mL min(-1) kg(-1)) and increased Q but V(s) did not change. Inactive fish were characterized by a high vagal tone (98.3 +/- 21.7%), and the tachycardia during digestion and exercise was exclusively due to a reduction of vagal tone, while the adrenergic tone remained low during all conditions. Intrinsic f(H), revealed after double autonomic blockade, was not affected by digestion (71 +/- 4 and 70 +/- 6 min(-1), respectively), indicating that non-adrenergic, non-cholinergic (NANC) factors do not contribute to the tachycardia during digestion in sea bass. (C) 2010 Elsevier Inc. All rights reserved.
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Jourdan-Pineau, H., Dupont-Prinet, A., Claireaux, G., & McKenzie, D. J. (2010). An Investigation of Metabolic Prioritization in the European Sea Bass, Dicentrarchus labrax. Physiol. Biochem. Zool., 83(1), 68–77.
Résumé: We investigated the ability of European sea bass (Dicentrarchus labrax) to respond simultaneously to the metabolic demands of specific dynamic action (SDA) and aerobic exercise and how this was influenced by moderate hypoxia (50% air saturation). At 3 h after feeding in normoxia at 20 degrees C, SDA raised the instantaneous oxygen uptake (Mo(2)) of sea bass by 47% +/- 18% (mean +/- SEM, N = 7) above their standard metabolic rate (SMR) when fasted. This metabolic load was sustained throughout an incremental exercise protocol until fatigue, with a 14% +/- 3% increase in their maximum aerobic metabolic rate (MMR) relative to their fasted rate. Their incremental critical swimming speed (U(crit)) did not differ between fasted and fed states. Thus, in normoxia, the bass were able to meet the combined oxygen demands of SDA and aerobic exercise. In hypoxia, the sea bass suffered a significant decline in MMR and U(crit) relative to their normoxic performance. The SDA response was similar to normoxia (84% +/- 24% above fasted SMR at 3 h after feeding), but although this load was sustained at low swimming speeds, it gradually disappeared as swimming speed increased. As a result, the hypoxic sea bass exhibited no difference in their fasted versus fed MMR. Hypoxic U(crit) did not, however, differ between fasted and fed states, indicating that the sea bass deferred their SDA to maintain exercise performance. The results demonstrate that, in normoxia, the sea bass possesses excess cardiorespiratory capacity beyond that required for maximal aerobic exercise. The excess capacity is lost when oxygen availability is limited in hypoxia, and, under these conditions, the sea bass prioritize exercise performance. Thus, environmental conditions (oxygen availability) had a significant effect on patterns of oxygen allocation in sea bass and revealed intrinsic prioritization among conflicting metabolic demands.
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McKenzie, D. J., Steffensen, J. F., Taylor, E. W., & Abe, A. S. (2012). The contribution of air breathing to aerobic scope and exercise performance in the banded knifefish Gymnotus carapo L. J. Exp. Biol., 215(8), 1323–1330.
Résumé: 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 degrees 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-O2=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.
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Wang, T., Lefevre, S., Iversen, N. K., Findorf, I., Buchanan, R., & McKenzie, D. J. (2014). Anaemia only causes a small reduction in the upper critical temperature of sea bass: is oxygen delivery the limiting factor for tolerance of acute warming in fishes? Journal of Experimental Biology, 217(24), 4275–4278.
Résumé: To address how the capacity for oxygen transport influences tolerance of acute warming in fishes, we investigated whether a reduction in haematocrit, by means of intra-peritoneal injection of the haemolytic agent phenylhydrazine, lowered the upper critical temperature of sea bass. A reduction in haematocrit from 42 +/- 2% to 20 +/- 3% (mean +/- s.e.m.) caused a significant but minor reduction in upper critical temperature, from 35.8 +/- 0.1 to 35.1 +/- 0.2 degrees C, with no correlation between individual values for haematocrit and upper thermal limit. Anaemia did not influence the rise in oxygen uptake between 25 and 33 degrees C, because the anaemic fish were able to compensate for reduced blood oxygen carrying capacity with a significant increase in cardiac output. Therefore, in sea bass the upper critical temperature, at which they lost equilibrium, was not determined by an inability of the cardio-respiratory system to meet the thermal acceleration of metabolic demands.
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