Variations in temperature acclimation effects on glycogen storage, hypoxia tolerance and swimming performance with seasonal acclimatization in juvenile Chinese crucian carp

The aim of this study was to test whether temperature acclimation (10 vs 20 °C) effects on tissue glycogen content, hypoxia tolerance, and swimming performance of Chinese crucian carp (Carassius auratus) varied with seasonal acclimatization (winter vs spring) and potential combined interactions. Both the routine metabolic rate (M·O2rout) and critical oxygen tension (Pcrit) of the M·O2rout increased significantly with temperature, whereas the seasonal acclimatization showed no significant effect. Only the high temperature group that acclimatized in spring showed a significantly higher aquatic surface respiration (ASRcrit) value compared with the other three groups. Fish in spring tended to show ASR behavior at higher oxygen tension compared with those in winter, which might have been caused by a more active lifestyle. Time to show LOE prolonged by 25-34% under low temperature. Spring fish showed 20% shorter LOE duration at 10 °C, whereas the difference tended to vanish at 20 °C. Glycogen contents in both liver and muscle were higher in winter than spring. The liver and muscle glycogen content decreased by 5-42% after exposure to anoxic conditions, whereas the magnitude was much smaller in spring. When fish swam in normoxic conditions, fish in higher temperatures showed higher critical swimming speed (Ucrit) than low temperature (5.49 vs 3.74 BL s−1 in winter and 4.27 vs 3.21 BL s−1 in spring), whereas fish in winter also showed higher Ucrit than fish in spring for each temperature. However, when fish swam in hypoxic waters, fish in higher temperatures showed a more profound decrease (52-61%) in Ucrit compared to those in lower temperature (25-27%). Fish in lower temperatures that had acclimatized in winter showed the highest Ucrit, which might have been caused by higher glycogen storage. The present study suggested that both glycogen storage and alterations in lifestyle had profound effects on hypoxia tolerance and swimming performance, which resulted in a profound difference between seasons and acclimation temperatures.