The effects of body mass (M) and temperature (T) on routine metabolic rate (mR) were assessed in the largemouth bronze gudgeon Coreius guichenoti, from Three Gorges Reservoir, Yangtze River, China. The mR increased with increasing M by factors (b-value in the equation mR = aMb) of 0·843, 0·800, 0·767, 0·788 and 0·822 at 10, 15, 20, 25 and 30° C, respectively. A significant interaction between M and T on mR was observed. The variation in the b-value at different T suggests that the b-values were not consistent with the universal allometric exponent 0·75. After controlling for M, the relationship between the normalized standard metabolic rate (mS, mg O2 kg−1 h−1) and T was described by an exponential equation: mS = 9·89e(0·093T). The results indicate that the effects of M on mR depend on T. The increased water temperature induced by dam construction on the Yangtze River may cause a marked increase in energy demand by this species, with potential ecological consequences.