title: An examination of the metabolic processes underpinning critical swimming in Atlantic cod (Gadus morhua L.) using in vivo 31P-NMR spectroscopy.
abstract: Traditionally, critical swimming speed has been defined as the speed when a fish can no longer propel itself forward, and is exhausted. To gain a better understanding of the metabolic processes at work during a U(crit) swim test, and that lead to fatigue, we developed a method using in vivo (31)P-NMR spectroscopy in combination with a Brett-type swim tunnel. Our data showed that a metabolic transition point is reached when the fish change from using steady state aerobic metabolism to non-steady state anaerobic metabolism, as indicated by a significant increase in inorganic phosphate levels from 0.3+/-0.3 to 9.5+/-3.4 mol g(-1), and a drop in intracellular pH from 7.48+/-0.03 to 6.81+/-0.05 in muscle. This coincides with the point when the fish change gait from subcarangiform swimming to kick-and-glide bursts. As the number of kicks increased, so too did the Pi concentration, and the pH(i) dropped. Both changes were maximal at U(crit). A significant drop in Gibbs free energy change of ATP hydrolysis from -55.6+/-1.4 to -49.8+/-0.7 kJ mol(-1) is argued to have been involved in fatigue. This confirms earlier findings that the traditional definition of U(crit), unlike other critical points that are typically marked by a transition from aerobic to anaerobic metabolism, is the point of complete exhaustion of both aerobic and anaerobic resources.
authors.affiliation: Alfred Wegener Institut fuer Polar und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany. Glenn.Lurman@awi.de
authors.forename: Glenn J
authors.initials: GJ
authors.lastname: Lurman
authors.forename: Christian H
authors.initials: CH
authors.lastname: Bock
authors.forename: Hans-O
authors.initials: HO
authors.lastname: Pörtner
mesh_terms: D000818:Animals; D004734:Energy Metabolism; D005221:Fatigue / Q000378:metabolism; D048389:Gadus morhua / Q000378:metabolism / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D019906:Nuclear Magnetic Resonance, Biomolecular; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism; D010759:Phosphorus Isotopes; D005082:Physical Exertion; D013550:Swimming / Q000502:physiology*
chemical_list: D010710:Phosphates; D010759:Phosphorus Isotopes