WU, S.H.*; MILLIGAN, C.L.; The University of Western Ontario, London: To eat or not to eat: The effect of food on metabolic recovery from a bout of exhaustive exercise in adult and juvenile rainbow trout white muscle

Exhaustive exercise depletes muscle glycogen in both juvenile (~ 5g) and adult (~ 160g) trout. In adult fish, muscle glycogen recovers approximately 8 hrs post-exercise but is incomplete in juveniles even at 24 hrs post-exercise. Traditionally, these studies have been done on fasted fish. The limitation of food following exercise may delay complete muscle glycogen recovery in both adult and juvenile fish. To test this hypothesis, fish were exercised and then fed (~ 4% body weight per feeding) at 0.5 and 6.5 hrs into recovery or fasted following exercise. White muscle was sampled at rest, immediately after exercise, as well as 1, 2, 4, 6, 12, and 24 hrs post-exercise. When fish are fed following exercise, muscle glycogen returns to pre-exercise levels in both adults (13.7 µmol glucosyl/g wet tissue ± 3.8) and juveniles (24 µmol glucosyl/g wet tissue ± 5.24) within 6 hrs of recovery. In contrast, in fasted juveniles, recovery of muscle glycogen is incomplete at 24 hrs post-exercise (16.1 µmol glucosyl/g wet tissue ± 2.6), but glycogen recovers within 12 hrs post-exercise in fasted adults (14.2 µmol glucosyl/g wet tissue ± 4.7). Lactate clearance was unaffected by feeding in both adults and juveniles. These results suggest that food enhances muscle glycogen recovery in both adults and juveniles presumably by providing the necessary extra energy for muscle glycogen resynthesis. In juveniles, energy is directed predominantly towards growth and development, while in adults, excess energy is stored as fat. Therefore, juveniles will likely depend on an external energy source to support muscle glycogen resynthesis more so than in adults.