To investigate the matebolize response of different physiological performances to decreased temperature of long-term high-temperature-acclimated juvenile qingbo (Spinibarbus sinensis),the experimental fish were reared at 15 or 25℃ for 8 weeks,respectively;then the temperature of the 25℃ group was decreased to 15℃(treatment group),and the temperature of the 15℃ group remained the same (control group).The thermal tolerance capacity (critical maximum temperature,CT_max and critical minimum temperature,CT_min),maximum sustainable swimming speed (critical swimming speed,U_crit),spontaneous activities (percent time spent moving (PTM) and total distance moved (TDM)),specific dynamic action (peak postprandial metabolic rate (PMR)),and growth performance (feed rate,feed efficiency,and weight gain) of fish in both temperature groups were measured at 1,2,4,and 8 weeks after the temperature was decreased.There was no significant difference in cold tolerance capacity as suggested by CT_min between the treatment and control groups,whereas the heat tolerance capacity,as suggested by CT_max of the treatment group,was significantly higher than that of the control group one week after the temperature decrease,and thereafter there was no difference between the groups.The temperature decrease resulted in a significant improvement of spontaneous activities suggested by higher PTM and TDM than those of the control group (P < 0.05),and such differences persisted throughout the experimental period.The U_crit of the treatment group was significantly lower than that of the control group at 1 and 2 weeks after the temperature decrease,and the impaired swimming capacity disappeared after 4 weeks of temperature acclimation.The PMR and SDA duration did not show any differences between the treatment and control groups from 1 to 4 weeks after the temperature decrease.The food efficiency and weight gain of the treatment group were generally lower than those of the control group,although the treatment group unusually showed a higher food rate.This suggested that there were profound differences among response speeds of different physiological performances to decreased temperature,which were possibly related to differences in their ecological correlations and underlying mechanisms.The temperature decrease in the treatment group resulted in impaired growth performance,which was mainly due to the additional energy expenditure involved in thermal stress responses,regulation of physiological functions,and elevated spontaneous activities.