An examination of the metabolic processes underpinning critical swimming in Atlantic cod (Gadus morhua L.) using in vivo 31P-NMR spectroscopy

• Published in: Journal of Experimental Biology
• Main Authors: Lurman, Glenn J., Bock, Christian H., Pörtner, Hans-O.
• Format: Text
• Language: English
• Published: Company of Biologists 2007
• Subjects: Research Article; atlantic cod; Gadus morhua
• Online Access: http://jeb.biologists.org/cgi/content/short/210/21/3749; https://doi.org/10.1242/jeb.008763

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 31P-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.