Lipid and protein catabolism contribute to aerobic metabolic responses to exhaustive exercise during the protracted spawning run of the lamprey Geotria australis
This paper has integrated new and past data to elucidate how lipid, protein and glycogen metabolism contribute to generating the ATP required by the southern hemisphere lamprey Geotria australis during its ~ 13–15 months, non-trophic upstream spawning migration. Energy is required for maintenance, swimming, the development of gonads and secondary sexual characters and spawning and post-spawning activities. Plasma and muscle metabolites were measured in animals subjected to an exercise-recovery regime at the commencement and completion of the spawning run. The present study demonstrated the following. At all stages of the migration, plasma glucose and glycerol concentrations increased during exercise and then declined, whereas plasma FFAs exhibited the reverse trend. During exercise and recovery, alanine declined and ammonia increased in the plasma of early migrants, while the opposite occurred in mature males. Following exercise, muscle alanine rose and then declined in early migrants, but declined and then rose in mature males. The composite data emphasise that, while the same catabolic processes are employed by both sexes early in the migration, when animals are immature, they differ markedly between the sexes as they mature and then spawn, reflecting their different demands. Energy is supplied predominantly via anaerobic metabolism in early migrants, but by anaerobic and aerobic metabolism in prespawning females and by aerobic metabolism in mature males and spent females. Although proteolysis is limited early in the migration, it is employed extensively during maturation and particularly by females, which undergo a substantial reduction in length in the lead-up to spawning.