Abstract: In order to investigate the effects of heating/cooling rate and acclimation mode on the thermal tolerance of different fish, the relevant parameters, such as critical thermal maxima (CT_max), critical thermal minima (CT_min), lethal thermal maxima (LT_max) and lethal thermal minima (LT_min), were measured in juvenile zebrafish (Danio rerio) and guppy (Poecilia reticulata) after 2 weeks of acclimation at 28 or 26-30 ℃. All the parameters were determined at a given heating/cooling rate (0.03, 0.1, 0.3, 1, and 3 ℃·min^-1). Our results showed that the heating/cooling rate had marked influence on all the parameters (P<0.05). The CT_min and LT_min of both fish species decreased with the decrease of cooling rate, whereas the CT_max and LT_max decreased or remained unchanged under the low heating rate. The CT_min and LT_max were significantly affected by acclimation mode (P<0.05). Compared with constant temperature acclimation, dielfluctuating temperature resulted in increasing trends in LT_max of both fish species and a decreased trend in CT_min of guppy. Moreover, the thermal tolerance amplitudes of zebrafish were wider than that of guppy. The results indicated that the heating/cooling rate had more pronounced effect on the measurement of cold tolerance than heat tolerance in fish, and that the heating/cooling rate would produce more influence on fish with narrower thermal tolerance amplitude.

Key words: ecotone, soil water, Heihe River., spatial distribution, temporal stability