The effect of acclimation to hypoxia and sustained exercise on subsequent hypoxia tolerance and swimming performance in goldfish (Carassius auratus).

The objective of this study was to determine whether acclimation to hypoxia and sustained exercise would increase hypoxia tolerance (as indicated by a decrease in critical oxygen tension, P(crit)) and swimming performance in goldfish (Carassius auratus), and to investigate the relationship between changes in performance and gill remodelling and tissue metabolic capacity. Goldfish were acclimated to either hypoxia (48 h at 0.3 mg O(2) l(-1)) or sustained exercise (48 h at 70% of critical swimming speed, U(crit)) and then P(crit) and U(crit) were determined in normoxia (10 mg O(2) l(-1)) and hypoxia (1 mg O(2) l(-1)) and compared with values from control fish. Acclimation to both hypoxia and sustained exercise improved hypoxia tolerance (P(crit) was reduced by 49% and 39%, respectively), which was associated with an increase in lamellar surface area (71% and 43%, respectively) and an increase in blood [Hb] (26% in both groups). Exercise acclimation also resulted in a decrease in routine ( ). Acclimation to both hypoxia and sustained exercise resulted in a significant increase in U(crit) in hypoxia (18% and 17%, respectively), which was associated with an increase in maximal O(2) consumption rate at U(crit) ( ; 35% and 39%, respectively). While hypoxia acclimation resulted in an increase in U(crit) in normoxia, acclimation to sustained exercise did not improve subsequent swimming performance in normoxia. This lack of improvement was possibly due to depleted oxidizable substrates during exercise acclimation.